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Dean Pomerleau

Cold Exposure & Other Mild Stressors for Increased Health & Longevity

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More BAT → Better Bone Health

 

OK - I lied at the end of my last post when I said my next post would be about a new anabolic pathway that cold exposure (CE) employs to build up things like BAT tissue, bone tissue, immune system cells, and mitochondria in muscles. After getting part way through composing the post, I realized I've neglected to post much of the cool evidence that CE is good for building up and maintaining bone mineral quantity, not just quality like we think (hope?) CR is doing. Rather than survey the literature on this myself, I found a really good recent review [1], entitled The "Skinny" on brown fat, obesity, and bone that did the job for me. Here is an extended quote from that paper, along with some commentary and the references it mentions below:

 

In humans and in animal models, there is a consistent positive association between metabolically active BAT and bone mass, although it remains unclear whether BAT has direct osteogenic effects, or whether bone and BAT are positively correlated with a third factor, such as lean body mass. In humans, the quantity of cold-activated BAT was positively related to bone mineral density (BMD) in young, lean women [2], and to femoral total area, cross-sectional area,and thigh muscle area in men and women across wide ranges of age and BMI [3]. Lee et al.[4] found a positive correlation of active BAT and BMD in female subjects, but not in males, and BAT vol-ume was also a significant predictor of femoral total cross-sectional area and cortical bone area in children and adolescents [5]. In both younger and older subjects, the positive relationship between BAT and bone mass may be mediated by positive effects of muscle tissue on both BAT mass and bone mass [5][4].

 

Retaining bone mass as well as bone quality "across wide ranges of age and BMI" sounds pretty good right? 

 

Study [2] was particularly interesting. It included 15 female participants divided into three groups of 5 - anorexic (AN) women (BMI 18.3 - not too anorexic!), recovered anorexic (AN-R) women (BMI 22.4) or health control (HC) women (BMI 21.9 - slimmer than recovered anorexics!).The researchers tested the women's BAT level after overnight cold exposure, and then compared BAT levels with measures of their bone health. They found 80% of HC women had measureable BAT, compared with only 20% of AN and 40% (really only 20% - see graph below) of AN-R women. Once again (like in PMID 23393181 discussed here and here) we see that a history of eating too few calories (perhaps coupled with inadequate nutrition) results in depletion of BAT. But even more interesting, the amount of BAT the women possessed was strongly correlated with their bone mineral density at a number of sites:

 

Including data of BAT-positive and BAT-negative subjects, there was a positive correlation between BAT and BMD of the femoral neck (r = 0.63; P = 0.01), total hip (r = 0.58; P = 0.02), total body (r = 0.60; P = 0.02), lateral lumbar spine (r = 0.51; P = 0.05), and total lumbar spine (r = 0.67; P = 0.006) (Fig. 2), which remained significant after controlling for BMI and disease status (P = 0.04).

 

Here is the reference Figure 2:

 

yPqEmol.png

 

As you can see, 4 out of 5 AN women (black circles) had zero BAT, and had the lowest BMD in the study. The one AN women who had BAT, had quite a bit, and also had quite good BMD. Similarly for the one women in the AN-R group (red squares) who exhibited significant BAT, i.e. ↑ BAT → ↑ BMD. In the four healthy control women (green triangles) who exhibited BAT, increasing amounts of BAT were associated with increasing BMD in a strikingly consistent relationship. And notice from the quote above, and from this one:

 

There was no association between BAT and BMI, weight or percent [of Ideal Body Weight] (P = 0.6–0.8).

 

that BAT content, BMI/weight and BMD were not all tightly correlated together. In particular, women could have a high bone mass despite being thin, as long as they had detectable BAT. The authors end the paper with the following statement:

 

BAT may be involved in the regulation of stem cell differentiation into the bone lineage at the expense of adipogenesis.

 

Churning out bone cells rather than fat cells even in thin folks as a result of having BAT sounds darn appealing for skinny CR folks concerned about maintaining bone health.

 

But you might be saying, couldn't be just a result of the weight loss history of the AN and AN-R women? That is, perhaps the AN and AN-R women were depleted of both BAT and bone mass as a result of past or present severe weight loss and/or poor nutrition. 

 

A more recent study [3] by the same authors as [2] seems to put that criticism to rest. It found a similar result as seen above in [2] across 19 men and 86 women of various ages (19-77) and BMIs (15.7 - 48.9):

 

There were positive correlations between BAT volume and total femoral CSA [cross sectional area] and cortical CSA, independent of age, BMI and history of malignancy (P<0.05)... When total femoral CSA was entered as a dependent variable and BAT volume, age and BMI as independent variables in a forward stepwise regression model, BAT volume was the only predictor of total femoral CSA. When femoral cortical CSA was entered as a dependent variable and BAT volume, age and BMI as independent variables, BAT volume was the only predictor of femoral cortical CSA.

 

OK you say, but [2] was all women and [3] had only 19 men vs 86 women. Is this positive BAT-bone connection just a girl thing? Nope:

 

Separate analyses in men and women showed more BAT in men and stronger correlations between femoral structure and BAT in men compared to women, despite smaller number of male subjects in our study. This suggests that the BAT-bone connection might be stronger in men.

 

The same positive correlation between BAT and bone health was observed across 40 children and teenagers as well [5]:

 

Multiple regression analyses indicated that the volume of BAT predicted femoral cross-sectional area and cortical bone area, even after accounting for height, weight, and gender.

 

In summary, once again we see having BAT correlates with an important health / longevity benefit - in this case increased bone mass, independent of body weight. As the authors of [1] say, it's unclear whether BAT is causally involved in improved bone health or simply correlated with it remains to be determined. I'd say it's likely to be something in the metabolic program induced by cold exposure, but more on that in my next post.

 

This positive BAT-bone connection is particularly exciting because increased bone mass is not just a health benefit that CR fails to offer, CR actually results in dramatically reduced bone mineral density. Despite some promising hints that CR bones may be lighter but not more brittle, reduced bone mass remains a serious concern for many of us and has been the downfall of at least one former CR veteran

 

This is one more reason it makes sense to consider combining one's practice of CR with cold exposure.

 

I promise in my next post to address the metabolic pathway that might allow this sort of anabolic activity without requiring increased insulin, IGF-1 or any of the other usual growth-promoting agents, the elevation of which can have serious downsides for health & longevity. [sorry - it wasn't my next post, but here is a link to it].

 

--Dean

 

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[1] Am J Phys Anthropol. 2015 Feb;156 Suppl 59:98-115. doi: 10.1002/ajpa.22661. Epub 

2014 Nov 11.
 
The "Skinny" on brown fat, obesity, and bone.
 
Devlin MJ(1).
 
 
The discovery that metabolically active brown fat is present in humans throughout
ontogeny raises new questions about the interactions between thermoregulatory,
metabolic, and skeletal homeostasis. Brown adipose tissue (BAT) is distinct from 
white adipose tissue (WAT) for its ability to burn, rather than store, energy.
BAT uniquely expresses uncoupling protein-1 (abbreviated as UCP1), which diverts 
the energy produced by cellular respiration to generate heat. While BAT is found 
in small mammals, hibernators, and newborns, this depot was thought to regress in
humans during early postnatal life. Recent studies revealed that human BAT
remains metabolically active throughout childhood and even in adulthood,
particularly in response to cold exposure. In addition to the constitutive BAT
depots present at birth, BAT cells can be induced within WAT depots under
specific metabolic and climatic conditions. These cells, called inducible brown
fat, "brite," or beige fat, are currently the focus of intense investigation as a
possible treatment for obesity. Inducible brown fat is associated with higher
bone mineral density, suggesting that brown fat interacts with bone growth in
previously unrecognized ways. Finally, BAT may have contributed to climatic
adaptation in hominins. Here, I review current findings on the role of BAT in
thermoregulation, bone growth, and metabolism, describe the potential role of BAT
in moderating the obesity epidemic, and outline possible functions of BAT across 
hominin evolutionary history.
 
© 2014 American Association of Physical Anthropologists.
 
PMID: 25388370
 
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[2] J Clin Endocrinol Metab. 2012 Apr;97(4):E584-90. doi: 10.1210/jc.2011-2246. Epub 
2012 Jan 18.
 
Young women with cold-activated brown adipose tissue have higher bone mineral
density and lower Pref-1 than women without brown adipose tissue: a study in
women with anorexia nervosa, women recovered from anorexia nervosa, and
normal-weight women.
 
Bredella MA(1), Fazeli PK, Freedman LM, Calder G, Lee H, Rosen CJ, Klibanski A.
 
 
CONTEXT: Anorexia nervosa (AN) is associated with depletion of body fat, loss of 
bone mineral density (BMD), and impaired thermogenesis. Brown adipose tissue
(BAT) is lower in obese individuals and decreases during aging. Recent studies
have suggested a link between BAT and bone metabolism.
OBJECTIVE: Our objective was to investigate the presence and quantity of BAT in
patients with AN, recovered AN (AN-R), and normal-weight controls and to study
the relationship between BAT and BMD and body composition and investigate
hormonal predictors of BAT.
DESIGN AND SETTING: This was a cross-sectional study at a clinical research
center.
PATIENTS: Patients included 15 women: five with AN (mean age 30 ± 6.3 yr), five
AN-R, and five healthy nonobese controls of comparable age.
MAIN OUTCOME MEASURES: Cold-activated BAT was determined by
fluorodeoxyglucose-positron emission tomography/computed tomography. BMD of
total-body, spine, and hip, fat and lean mass was determined by dual-energy x-ray
absorptiometry. Single-slice magnetic resonance imaging at L4 was done for
abdominal fat compartments, and preadipocyte factor-1 (Pref-1), T₃, and T₄ were
measured.
RESULTS: Within the AN group, one of five; in the AN-R group, two of five; and in
the healthy nonobese control group, four of five subjects were BAT positive.
Subjects were divided into groups based on the presence (n = 7) or absence (n =
8) of BAT. Both groups were of comparable age and body mass index. Women with BAT
had higher total-body BMD, higher T₃, and lower Pref-1 compared with women
without BAT. There was a positive correlation between BAT and BMD that remained
significant after controlling for disease status and body mass index.
CONCLUSION: Young women with AN have low cold-activated BAT, which may be due to 
impaired BAT thermogenesis. Young women with BAT have higher BMD and lower Pref-1
compared with women without BAT, suggesting that BAT may be involved in the
regulation of stem cell differentiation into the bone lineage at the expense of
adipogenesis.
 
PMCID: PMC3319179
PMID: 22259053
 
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[3] Bone. 2014 Jan;58:55-8. doi: 10.1016/j.bone.2013.10.007. Epub 2013 Oct 17.

Positive effects of brown adipose tissue on femoral bone structure.

Bredella MA(1), Gill CM, Rosen CJ, Klibanski A, Torriani M.

Free full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3855336/

PURPOSE: Recent studies suggest a link between brown adipose tissue (BAT) and
bone. The purpose of our study was to investigate the effects of BAT on femoral
bone structure.
MATERIALS AND METHODS: We studied 105 patients (19 m, 86 f. mean age 45.5±16.1
years) who underwent F18-FDG positron emission tomography/computed tomography
(PET/CT) for benign etiologies (n=20) or follow-up of successfully treated
malignancies (n=85); mean time between PET/CT and last form of treatment was
14.8±18.0 months. BAT volume by PET/CT; femoral bone structure by CT (total
femoral cross-sectional area (CSA), cortical CSA); and thigh muscle CSA and thigh
subcutaneous fat CSA by CT was assessed.
RESULTS: There were positive correlations between BAT volume and total femoral
CSA and cortical CSA, independent of age, BMI and history of malignancy (p<0.05).
BAT volume correlated positively with thigh muscle CSA and thigh fat CSA
(p<0.05). When total femoral CSA was entered as a dependent variable and BAT
volume, age and BMI as independent variables in a forward stepwise regression
model, BAT volume was the only predictor of total femoral CSA. When femoral
cortical CSA was entered as a dependent variable and BAT volume, age and BMI as
independent variables, BAT volume was the only predictor of femoral cortical CSA.
CONCLUSION: BAT volume is a positive predictor of femoral bone structure and
correlates positively with thigh muscle and subcutaneous fat, possibly mediated
by muscle. These results provide further evidence of a positive effect of BAT on
bone.

© 2013.

PMCID: PMC3855336
PMID: 24140784

 

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[4] Osteoporos Int. 2013 Apr;24(4):1513-8. doi: 10.1007/s00198-012-2110-y. Epub 2012 

Aug 14.
 
Cold-activated brown adipose tissue is an independent predictor of higher bone
mineral density in women.
 
Lee P(1), Brychta RJ, Collins MT, Linderman J, Smith S, Herscovitch P, Millo C,
Chen KY, Celi FS.
 
 
In animals, defective brown adipogenesis leads to bone loss. Whether brown
adipose tissue (BAT) mass relates to bone mineral density (BMD) in humans is
unclear. We determined the relationship between BAT mass and BMD by
cold-stimulated positron-emission tomography (PET) and dual-energy X-ray
absorptiometry (DXA) in healthy volunteers. Higher BAT mass was associated with
higher BMD in healthy women, but not in men, independent of age and body
composition.INTRODUCTION: Contrary to the traditional belief that BAT is present 
only in infants, recent studies revealed significant depots of BAT present in
adult humans. In animals, defective brown adipogenesis leads to bone loss. While 
white adipose tissue mass is a known determinant of BMD in humans, the
relationship between BAT and BMD in humans is unclear. We thus examined the
relationship between BAT and BMD in healthy adults.
METHODS: BAT volume (ml) and activity (standard uptake value) were determined by 
18F-fluorodeoxyglucose PET after overnight mild cold exposure at 19 °C, and BMD
was determined by DXA.
RESULTS: Among 24 healthy adults (age 28±1 years, F=10), BAT volumes were
82.4±99.5 ml in women and 49.7±54.5 ml in men. Women manifested significantly
higher BAT activity, by 9.4±8.1% (p=0.03), than men. BAT volume correlated
positively with total and spine BMD (r2=0.40 and 0.49, respectively, p<0.02) in
women and remained a significant predictor after adjustment for age, fat, and
lean body mass (p<0.05). Total and spine BMD were higher in women who harbored
visually detectable BAT on PET images than those without by 11±2% (p=0.02) and
22±2% (p<0.01), respectively. No associations were observed between BAT
parameters and BMD in men.
CONCLUSIONS: This study demonstrated higher BMD among healthy women with more
abundant BAT, independent of age and other body compositional parameters. This
was not observed in men. The data suggest that brown adipogenesis may be
physiologically related to modulation of bone density.
 
PMID: 22890364
 
------------
[5] J Clin Endocrinol Metab. 2012 Aug;97(8):2693-8. doi: 10.1210/jc.2012-1589. Epub
2012 May 16.
 
Brown adipose tissue and its relationship to bone structure in pediatric
patients.
 
Ponrartana S(1), Aggabao PC, Hu HH, Aldrovandi GM, Wren TA, Gilsanz V.
 
Author information: 
(1)Department of Radiology, Viterbi School of Engineering, University of Southern
California, Los Angeles, California 90027, USA.
 
CONTEXT: Emerging evidence suggests a possible link between brown adipose tissue 
(BAT) and bone metabolism.
OBJECTIVE: The objective of this study was to examine the relationships between
BAT and bone cross-sectional dimensions in children and adolescents.
DESIGN: This was a cross-sectional study.
SETTING: The study was conducted at a pediatric referral center.
PATIENTS: Patients included 40 children and teenagers (21 males and 19 females)
successfully treated for pediatric malignancies.
INTERVENTIONS: There were no interventions.
MAIN OUTCOME MEASURES: The volume of BAT was determined by
fluorodeoxyglucose-positron emission tomography/computed tomography. Measures of 
the cross-sectional area and cortical bone area and measures of thigh musculature
and sc fat were determined at the midshaft of the femur.
RESULTS: Regardless of sex, there were significant correlations seen between BAT 
volume and the cross-sectional dimensions of the bone (r values between 0.68 and 
0.77; all P ≤ 0 .001). Multiple regression analyses indicated that the volume of 
BAT predicted femoral cross-sectional area and cortical bone area, even after
accounting for height, weight, and gender. The addition of muscle as an
independent variable increased the predictive power of the model but
significantly decreased the contribution of BAT.
CONCLUSIONS: The volume of BAT is positively associated with the amount of bone
and the cross-sectional size of the femur in children and adolescents. This
relation between BAT and bone structure could, at least in part, be mediated by
muscle.
 
PMCID: PMC3410267
PMID: 22593587

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Dean - regarding your "Ikeno et al" analysis, that is very much in line with what my thoughts were when I read it, and I was right in thinking you would do a much better job of analyzing and articulating it than I could, thanks once again for all the work. I'm tempted to send your analysis to Professor A. Richardson but I have a feeling he won't respond <_<.  I wonder what the best way is to get researchers to improve on otherwise sloppy CR research? 

 

At any rate, CE just keeps looking better and better.  Hope you don't give yourself hypothermia though!

That graph you posted showing blood glucose comparisons between warm/cold exposed individuals is also remarkable, and aligns with my personal observations/anecdotes so far with CE.  CE is a game changer as far as I'm concerned, and I expect it to change the way CR is practiced.  

 

 

Regards,

Gordo

Edited by Gordo

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Hi Gordo,
 
I'm glad someone (other than me) has found some of my analysis useful! I too am quite excited about the potential for CE to improve upon the benefits of CR.
 
Regarding:
Hope you don't give yourself hypothermia though!

 

It seems quite the contrary based on personal experience. In particular, I find myself like Eric in the CoolFatBurner.com videos, becoming more and more comfortable in colder and colder conditions everyday. My body is clearly adapting to the cold. At this moment, I'm pedalling away on my stationary bike at a very modest pace (my heart rate is 91 BMP) wearing just bike shorts. The ambient temperature is 62 degF here in my basement, and I've got 3 fans blowing on me. And I'm still feeling a bit on the warm side.

 

The other thing I've noticed is improved aerobic capacity during exercise. I live in a very hilly neighborhood and I used to get somewhat winded and my legs got tired running up several of the big hills during my twice daily runs. Now I feel much more aerobicly strong. I'm not eating any more or gaining any weight. And I haven't changed my exercise routine either.

 

I thought it might be a result of an increase in blood oxygen carrying capacity, but I just had a CBC blood test done as a followup to my Dr's concern at my yearly checkup a few months ago that I might be borderline anemic (despite no symptoms). My latest hemoglobin was 13.2 g/dl, right at the bottom of the reference range, as was my ferritin (30 ng/dl). So it would appear my blood's oxygen carrying capacity and iron stores hasn't changed much, although they are up a bit from my last round of tests. 

 

The only other significant change in my CBC was my white blood cell count (WBC) went up to 4.5, into the low end of the reference range (4.0 - 10.5). This seems like it could be a sign of the improved immunocompetence induced by CE with adequate calories that I talked about as being the advantage enjoyed by the Walford cold mice. The Walford CE+CR mice ate enough calories to keep their immune system counts adequate, enabling them to avoid pneumonia and thereby live longer than both the Walford's warm-CR mice and longer than the starved and therefore immunocompromised CE+CR mice in the Ikeno et al study discussed above. I'm hoping I'm like one of those Walford CE+CR mice!

 

Regarding my apparent improvements in aerobic capacity, I can only speculate that it may be a result of an increase in mitochondria in my muscles, like was observed as a result of cold exposure in the study I discussed several posts back in my big sarcolipin post.

 

It's pretty cool (pun intended) to the see apparent parallels between my own experience and the research on cold exposure.

 

--Dean

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I was amused and interested to come across this inspirational Under Armor "Rule Yourself" video of Michael Phelps' grueling training regime leading up to his bid for more Olympic gold in 2016, while reading this article on new studies that show better late life fitness (as measured quantitatively by leg strength) is associated with a reduced rate of cognitive decline.

 

What caught my eye was that at exactly 28sec into the video Michael can be seen throwing ice into a bathtub and then shivering while sitting in the tub at second 29. Don't blink or you'll miss it.

 

https://www.youtube.com/watch?v=Xh9jAD1ofm4

 

Of course, in seconds 30-32 Michael can be seen stuffing his face with what looks like eggs and french toast. Phelps is famous (or infamous) for reporting he eats about 12K calories per day when in heavy training. And I though ate a lot. The following video shows what he eats in a day. Pretty amazing quantity, most of it crap, including this breakfast:

 

NBC commentator Bob Costas rattled off Phelps' breakfast menu, which includes three sandwiches of fried eggs, cheese, lettuce, tomato, fried onions, mayonnaise, an omelet, a bowl of grits, three slices of French toast with powdered sugar, and three chocolate-chip pancakes. Without knowing the exact details of the portions, recipes, and ingredients, this meal probably contains roughly 3,000 calories, 

 

 

Later Phelps denied eating quite that much in the runup to Beijing, but he certainly ate a lot, and a lot of crap, while remaining amazingly thin:

 

michael_phelps_diet.jpg

 

Part of the reason he could eat so much and not get fat has to do with the number of miles he swims. But it also likely resulted from the huge amount of thermogenesis required to stay warm in a cold pool (water is a much better conductor of heat than air, so it sucks the heat out of a swimmer), and (if the above video is accurate) in the ice baths he takes.

 

He's an amazing example of a person pushing the envelope of human possibility. I admire the heck out of his athletic accomplishments, although some of his personal mistakes outside the pool have been troubling and hard to watch. But I'd say don't try that at home...

 

--Dean

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Just a couple of quick notes on your most recent blood test results, Dean,

 

Your resting heart rate went up.

 

Neutrophil:lymphocyte ratio marker of inflammation went south.

 

 

Neutrophil:lymphocyte ratio is positively related to type 2 diabetes in a large-scale adult population: a Tianjin Chronic Low-Grade Systemic Inflammation and Health cohort study.
Guo X, Zhang S, Zhang Q, Liu L, Wu H, Du H, Shi H, Wang C, Xia Y, Liu X, Li C, Sun S, Wang X, Zhou M, Huang G, Jia Q, Zhao H, Song K, Niu K.
Eur J Endocrinol. 2015 Aug;173(2):217-25. doi: 10.1530/EJE-15-0176. Epub 2015 May 7.
PMID: 25953830
 
Abstract
 
AIM:
 
It is widely known that inflammation is related to type 2 diabetes (T2D), but few studies have shown a direct relationship between the immune system and T2D using a reliable biomarker. Neutrophil:lymphocyte ratio (NLR) is an easy-to-analyze inflammation biomarker, but few studies have assessed the relationship between NLR and T2D. In order to evaluate how NLR is related to T2D, we designed a large-scale cross-sectional and prospective cohort study in an adult population.
 
SUBJECTS AND METHODS:
 
Participants were recruited from the Tianjin Medical University General Hospital-Health Management Centre. Both a baseline cross-sectional (n=87,686) and a prospective (n=38,074) assessment were performed. Participants without a history of T2D were followed up for ∼ 6 years (with a median follow-up of 2.7 years). Adjusted logistic and Cox proportional hazards regression models were used to assess relationships between the quintiles of NLR and T2D (covariates: age, sex, BMI, smoking status, drinking status, hypertension, hyperlipidemia, and family history of cardiovascular disease, hypertension, hyperlipidemia, or diabetes).
 
RESULTS:
 
The prevalence and incidence of T2D were 4.9% and 6.8/1000 person-years respectively. The adjusted odds ratio and hazard ratio (95% CI) of the highest NLR quintile were 1.34 (1.21, 1.49) and 1.39 (1.09, 1.78) (both P for trend <0.01) respectively as compared to the lowest quintile of NLR. Leukocyte, neutrophil, and lymphocyte counts do not significantly predict the eventual development of T2D.
 
CONCLUSION:
 
The present study demonstrates that NLR is related to the prevalence and incidence of T2D, and it suggests that NLR may be an efficient and accurate prognostic biomarker for T2D.

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Thanks for commenting Al.

 

You wrote:

 Your resting heart rate went up.

Yes, I've pointed that out that my resting heart rate has gone up several times recently (e.g. here), suggesting it's likely a result of an increase in epinephrine as a result of cold exposure. I didn't feel the need to mention it again when talking about my blood test.

 

Neutrophil:lymphocyte ratio marker of inflammation went south. [citing PMID 25953830 which found N:L to be a marker for low-grade inflammation and predictive of future diabetes development in a population of Chinese people]

You have got to be kidding Al. As I said, my WBC count went from well below the bottom end of the reference range to the low end of the reference range (4.5  RR 4.0 - 10.5).

 

As I also suggested, this seems more likely a case of building my immunocompetence as a result of cold exposure boosting my immune system rather than a sign of low-grade systemic inflammation. In fact it continues to surprise me how little inflammation I appear to experience - e.g. a complete lack of aches, pains or sore joints despite engaging in (admittedly low-impact & low-intensity) exercise over 9 hours per day, 7 days per week.

 

Regarding signs of diabetes. I just happened to do fasting and post-meal glucose tests yesterday and this morning. My fast glucose was 86 mg/dl. Ten minutes after completing my 3400+ kcal single daily meal, my glucose was 120 mg/dl. Fifteen minute later, after a chilly one mile run, my glucose was 107 mg/dl. I'd say I'm doing just fine in the glucose control department, and am at quite low risk of diabetes.

 

--Dean

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An Eco-Evolutionary Explanation for Synergistic Effects of CR and CE

 

All,

 

Consider this post a prelude and gentle introduction to my next post, which will be pretty technical in nature on the topic of metabolic pathways associated with CR & CE. Here I'm going to set the stage for that discussion.

 

I've long thought it helpful to think about the evolutionary explanation for the CR longevity effect. In summary, the idea is that during times of food shortage, mammals with genetic machinery that enables them to 'hunker down' and survive the famine by shifting scare caloric resources to bodily maintenance & repair, rather than growth and reproduction, would have a reproductive advantage and so such an adaptive metabolic program would become entrenched in the genes of our ancestors over time, and would still be part of our evolutionary endowment.

 

What I came to realize while researching the metabolic pathways of CR & CE is that chronic food shortage and chronic cold exposure would likely have occurred simultaneously with the seasons as our mammalian ancestors spread into new, less-hospitable niches after the extinction of the dinosaurs. In particular, consider what happens in winter everywhere except the tropics. It gets colder. What happens when it gets colder? Homeotherms need to spend more calories generating heat and food becomes more scarce, both because plants stops growing when it's cold, other animals hibernate or migrate and so aren't as readily available as food sources, and stores of food you've built up, either literally (e.g. squirrels & acorns) or as excess body fat, become depleted.

 

At such times the two stressors (cold & food shortage) would even be mutually reinforcing. A shortage of food in winter would force you to leave the relative warmth of your burrow or cave and venture out in search of food, exposing you to more cold. Depleting of your insulating fat stores as a result of wintertime food shortage would also increased thermogenic requirements. And the cooler ambient temperatures, your increased exposure to them via more foraging, and your reduced insulation would increase your calorie needs in order to support the greater physical activity and thermogenesis, thereby exacerbating your net calorie deficit. In other words, a calorie deficit leads to more cold exposure which leads to a greater calorie deficit.

 

If CR & CE co-occurred regularly, repeatedly and over sufficiently long stretches of our evolutionary history, I suggest it would make evolutionary sense for metabolic adaptations to the two stresses to work synergistically with one another to optimize an organism's chance of survival. In fact, if the two occurred with high enough correlation (e.g. every winter organisms face both starvation and hypothermia), the adaptation to both stresses could be considered a single package, for example filling in each other's gaps in order to tune to body's metabolism to maximize its chance of surviving. The body would come to assume CR & CE will occur simultaneously, and tune its metabolic response based on the combination of the two.

 

In modern times, with the advent of central heating and corner grocery stores, food shortages and cold exposure have become entirely avoidable, and separable. It's possible these days to have one without the other. In fact, many CRers do just that, restricting calories but eschewing the cold, on the assumption that, in the immortal words of (or will it be "words of immortal"?) Michael "absolute Calories are the key to the anti-aging effect," and so if I'm exposed to cold, I'll have to eat more calories and that will erase CR's benefits.

 
As discussed repeatedly in this thread, there are several lines of evidence that seem to directly contradict Michael's perspective on this, and instead support the idea that the health/longevity benefits of CR and CE are inextricably linked. First, it's easy to overlook the fact that virtually every CR rodent study ever conducted has combined CR & CE, by housing rats & mice singly at normal room temperature (~21 °C) whereas thermoneutrality for isolated rodents is ~30 °C. It is the rare exceptions to this co-occurrence of CR & CE in the CR literature that are informative and provide support for the thesis that CR & CE are co-dependent. They are, quite literally, the exceptions that prove the rule.
 
The classic example is the famous Holloszy (1985) "rats with cold feet" study [1] that kicked off this whole thread. Holloszy found that rats given ad lib access to food ate 44% more, weighed a bit less and live a bit longer than control mice kept at 'normal' housing temperatures, which we know are actually pretty chilly for rodents already. The cold rats were less than half as susceptible to cancer as the warmer rats, a benefit of cold exposure we've seen repeatedly in the literature discussed in this thread.  Ikeno et al [2] (discussed here) found almost the same thing, but even more cleanly, in their ad lib fed controls. Cold exposed (i.e. singly housed) ad lib mice ate 40% more, weighed almost exactly the same, and had an identical lifespan to warm (multiply-housed) ad lib mice.

 

What the Holloszy and Ikeno studies show is that cold exposure alone, without a large net deficit in calories (i.e. a net deficit that leaves the organism CR-thin) doesn't reduce health or longevity, and in fact it may increase health/longevity somewhat, e.g. by preventing cancer. But without a large net deficit in calories, cold exposure alone doesn't increase lifespan either. To get large health and lifespan benefits, CE needs to be combined with CR, in the form of a net calorie deficit sufficient to dramatically reduce body weight below normal. Alone CE doesn't cut it.

 

Conversely, Koizumi & Walford [3], found that CR without CE doesn't work either. Warm-housed CR mice didn't live any longer on average than cool-housed, ad lib fed controls, while cool-housed CR mice (who were fed more than warm-housed CR mice to maintain an identical body weight) lived a lot longer, largely again because they avoided cancer, unlike the warm-housed CR mice who were as cancer-prone as the controls.

 

What the Koizumi & Walford study shows is that CR, and the severe reduction in body weight that accompanies it, doesn't reduce health or longevity relative to controls. But without cold exposure, calorie restriction alone doesn't increase lifespan either. To get large health and lifespan benefits, CR needs to be combined with CE. Alone CR doesn't cut it.  

 

A final, sad example of a study where CR & CE were decoupled with unfortunate results was the CR monkey study. As discussed here, the NIA monkeys (who, unlike the UW monkeys, were a real test of whether CR works or not relative to a healthy, obesity-avoiding diet) were housed at an average daily temperature that was above thermoneutrality. And we all know the disappointing upshot, the NIA monkeys did not live longer than controls, despite eating significantly fewer calories, and being thinner throughout their lives. Once again we see that CR without CE doesn't work.

 

In short, the evidence strongly suggests that CR & CE are a package deal. You can't get substantial benefits from one without the other. You can't be thin and warm and expect to live a long time. You can't be chubby and cold and expect to live a long time. Thin and cold is what it takes.

 

I tried to argue above that this coupling makes sense from an evolutionary perspective. CR & CE were likely to co-occur on such a regular and consistent basis in our evolutionary history that the body's of our ancestors became tuned for maximal survival under the assumption that both would be present. And so one without the other fails to elicit the complete set of complex and complementary metabolic adaptations required to extend health and lifespan.

 

In my next post I promise to (finally) delve into an example of how this sort of complementarity between CR & CE manifests itself.

 

--Dean

 

------------------

[1] J Appl Physiol (1985). 1986 Nov;61(5):1656-60.

 
Longevity of cold-exposed rats: a reevaluation of the "rate-of-living theory".
 
Holloszy JO, Smith EK.
 
It has been postulated that increased energy expenditure results in shortened
survival. To test this "rate-of-living theory" we examined the effect of raising
energy expenditure by means of cold exposure on the longevity of rats. Male
6-mo-old SPF Long-Evans rats were gradually accustomed to immersion in cool water
(23 degrees C). After 3 mo they were standing in the cool water for 4 h/day, 5
days/wk. They were maintained on this program until age 32 mo. The cold exposure
resulted in a 44% increase in food intake (P less than 0.001). Despite their
greater food intake, the cold-exposed rats' body weights were significantly lower
than those of control animals from age 11 to 32 mo. The average age at death of
the cold-exposed rats was 968 +/- 141 days compared with 923 +/- 159 days for the
controls. The cold exposure appeared to protect against neoplasia, particularly
sarcomas; only 24% of the necropsied cold-exposed rats had malignancies compared
with 57% for the controls. The results of this study provide no support for the
concept that increased energy expenditure decreases longevity.
 
PMID: 3781978
 
----------------
[2] Ikeno Y, Hubbard GB, Lee S, Richardson A, Strong R, Diaz V, Nelson JF. Housing density does not influence the longevity effect of calorie restriction. J Gerontol A Biol Sci Med Sci. 2005 Dec;60(12):1510-7. PubMed PMID: 16424282. 
 
---------
[3] Mech Ageing Dev. 1996 Nov 29;92(1):67-82.
 
A tumor preventive effect of dietary restriction is antagonized by a high housing
temperature through deprivation of torpor.
 
Koizumi A(1), Wada Y, Tuskada M, Kayo T, Naruse M, Horiuchi K, Mogi T, Yoshioka
M, Sasaki M, Miyamaura Y, Abe T, Ohtomo K, Walford RL.
 
Author information: 
(1)Department of Hygiene, Akita University School of Medicine, Japan.
koizumi@med.akita-u.ac.jp
 
Energy restriction (ER) has proven to be the only effective means of retarding
aging in mice. The mechanisms of multiplicity of effects of ER on aging remain,
however, fragmentary. ER induces daily torpor, the induction of which is reduced 
by increasing the ambient temperature to 30 degrees C. The effects of preventing 
hypothermia in ER animals were studied in terms of the expected consequences of
ER on survival, disease pattern and a number of physiological parameters in
autoimmune prone MRL/lpr mice and lymphoma prone C57BL, 6 mice. The results
demonstrate that torpor plays a crucial role in the prevention of lymphoma
development but does not have an affect on other aspects of ER, such as
prevention of autoimmune diseases.
 
PMID: 9032756

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Thanks for the explanation of your increased heart rate.  I had thought the lower the better for a healthy young/middle-aged man.

 

A search http://www.ncbi.nlm.nih.gov/pubmed/?term=Neutrophil%3Alymphocyte-ratio+all-cause*shows that the ratio relates to the inflammation marker's influences and the risks of many different conditions.

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Al,

A search http://www.ncbi.nlm.nih.gov/pubmed/?term=Neutrophil%3Alymphocyte-ratio+all-cause*shows that the ratio relates to the inflammation marker's influences and the risks of many different conditions.

 

A quick search on "low white blood cell count" will bring up any number of negative health outcomes associated with too few white blood cells including cancer, autoimmune disease, anemia and some kinds of latent infections. Does that mean low WBC is bad for CRers? Not necessarily, at least not for the usual reasons.

 

But the truth is that CR studies do show that calorie restriction makes it harder to recover, and death more likely, once an infection has gotten a foothold, as a result of CR's immunosuppressive effects, as discussed here. So that is a concern CR folks should take seriously, since we don't live in a germ-free lab like CR mice do.

 

As I mentioned yesterday, my next (major) post in this thread will be how (biochemically) CR & CE may work synergistically to fill in each others shortcomings, with the immunosuppressive effects of CR being a prime example.

 

--Dean

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Hi Dean!

 

I found your proposed explanation of the disappointing findings of the NIA monkey study interesting:

 

A final, sad example of a study where CR & CE were decoupled with unfortunate results was the CR monkey study. As discussed here, the NIA monkeys (who, unlike the UW monkeys, were a real test of whether CR works or not relative to a healthy, obesity-avoiding diet) were housed at an average daily temperature that was above thermoneutrality. And we all know the disappointing upshot, the NIA monkeys did not live longer than controls, despite eating significantly fewer calories, and being thinner throughout their lives. Once again we see that CR without CE doesn't work.

 

  -- Saul

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A Biochemical Model of CR & CE Synergy

 

In this post I'm going to first talk about a possible solution to a bit of a mystery associated with the body's response to cold exposure, and then talk about it's implications for the synergy between CR & CE. It's going to get a bit technical, and somewhat speculative, so if you aren't a hardcore follower of this thread, you might just want to skip to the bottom to read the summary in the last three paragraphs.

 

The mystery I'm alluding to is the following: The primary metabolic responses found to accompany cold exposure are all quite anabolic in nature - involving the genesis of new BAT cells, the conversion of WAT cells to BAT cells by adding mitochondria and other cellular machinery to the WAT cells, the biosynthesis of new mitochondria in muscle cells to support thermogenesis in muscles, generating new immune system cells or creating new bone cells. Sure there may be sufficient calories available to support such anabolic activities (at least if you don't starve subjects on top of cold exposure like the Ikeno et al study discussed here). But triggering and orchestrating such anabolic activities is typically done through elevated insulin, IGF-1 and other growth factors. But cold exposure doesn't raise insulin or IGF-1, as discussed here, here, here and here. For example, [2] (discussed in detail here) found serum insulin levels were lower in mice exposed to 17 °C compared with normal room temperature, and insulin was even lower when cold exposure was combined with capsaicin. Study [3] found that IGF-1 was reduced in primates as a result of cold exposure.

 

So the mystery is how the body manages to build up these new tissues and cellular organelles without much in the way of circulating growth-promoting signalling molecules insulin and IGF-1, which are normally required to trigger this sort of biosynthesis, and which are thought to be deleterious to health and longevity. Put another way, how is it that CE seems to be able to mimic CR's beneficial effect of keeping insulin and IGF-1 low (and thereby promoting longevity), while still promoting maintenance & growth of important body tissues like bones and immune cells, rather than catabolizing them the way CR does?

 

This new study [1] (press release), sent to me by a shy CR veteran who I'm hoping will join these discussions, may suggest an answer. The paper is pretty dense, but the upshot can be summarized pretty succinctly. It found that catecholamines, like the noradrenaline released as a result of cold exposure, upregulate the conversion of white adipose tissue (WAT) to brown adipose tissue (BAT) via a pathway that includes PKA (protein Kinase A) increasing mTORC1 (mammalian target of rapamycin complex 1) activity, which in turn pulls the strings to promote BAT synthesis.

 

Did you say mTORC1? Isn't that the same as mTOR? Doesn't CR turns off mTOR as an important part of how it shifts the body from "growth and reproduction" mode to "maintenance & repair" mode? 

 

Yes! And that's where I think things get interesting...

 

Rather than activating MTOR/MTORC1 via the usual pathway, namely Insulin/IGF-1 → AKT → mTORC1, epinephrine (i.e. cold exposure), activates MTORC1 via the pathway Epinephrine → PKA → mTORC1. And this makes a big difference. You see, mTORC1 is a "complex" of proteins (hence the 'C' in its name). It's basically a core mTOR protein with little extra bits hanging off it. Together, these parts form a complex mini-factory, which the authors of [1] liken to a multi-function printer:

 

 Imagine mTORC1 is a machine with multiple capabilities, like a printer/copier/scanner. Energy-storage signaling [via Insulin/IGF1 pathway - DP] pushes one set of buttons and gets one outcome (fat storage), while PKA pushes another set to get a different outcome (conversion to brown fat).

 

In a nutshell, cold exposure programs that anabolic mTORC1 mini-factory in a way that causes it to churn out a different set of outputs & outcomes than if it is programmed by elevated Insulin/IGF-1, with beneficial results (i.e. turning WAT to BAT rather than synthesizing more WAT).

 

This result got my thinking about the relationship between CR & CE, and the possibility of synergy between them. If you haven't already, now would be a good time to (re)read the introductory post from yesterday that serves as a prelude to what I'm going to discuss next.

 

The discussion from here out can best be understood in reference to the three-panel diagram below. It represents three different metabolic milieus - CR only (left), CE only (middle) and CR + CE (right). It is a greatly simplified diagram of important metabolic pathways that I've synthesized based on several diagrams from review papers. I won't claim it is entirely complete or accurate. I'm sure Michael or Al might quibble over the details. But I've tried to highlight as best I can some of the most important pathways involved in the health & longevity benefits of CR and CE based on the available science, in a way I hope is comprehensible. 

 

Let's start with the "CR Only" metabolic milieu illustrated on the left:

 

pLdCgcM.png

 

The green-shaded regions represent pathways that are upregulated by CR, while the red regions show pathways that CR downregulates. First, we all know the CR upregulates the beneficial AMPK / SIRT1 / FOXO pathway(s), with pretty much unmitigated benefits in terms of insulin sensitivity, stress resistance and overall longevity goodness.

 

The red region is more interesting - due to its "double-edged sword" nature. It shows that by keeping insulin and IGF-1 low, CR does lots of good things, including improving insulin sensitivity, reducing systemic inflammation and in general slowing the accumulation of age-related damage. At the same time, it turns the mTOR / mTORC1 activity down/off. This has some good effects, like preventing accumulation of WAT and enabling autophagy (killing off) of rogue cells. But turning off mTORC1 has its downsides as well. In particular, mTORC1 is responsible for orchestrating many important anabolic processes, beyond just the browning of white fat talked about in [1]. For example, mTORC1 is important for promoting the growth of new bone cells [4], for differentiating/activating new lymphocytes in the immune system [5], including natural killer (NK) cells [6], which are particularly important for fighting cancer as discussed in a post on this thread a few days ago. Further, mTOR is critical for adult neurogenesis and hence maintaining a healthy brain [7]. Unfortunately I left off "Brain Cell Synthesis" from the bottom row of outcomes in the above diagrams, so you'll have to use your imagination. The other key benefit of mTOR activity I left off the diagram is protein synthesis to build and preserve skeletal muscles [8]. 

 

In short, by dramatically attenuating Insulin / IGF-1 signalling, CR prevents lots of bad health & longevity consequences, but also shuts down important anabolic activities like synthesizing BAT, bone, immune, muscle and brain cells. This is why many thoughtful CR practitioners harbor some concerns about the long term effects of CR on bone health, immunocompetence, muscle loss and cognition. In fact, there have been endless discussions on these forums (like this recent one) and on the email list before that about the possible downsides of very low IGF-1 resulting from serious CR, usually focused on concerns about bones, brains and/or brawn

 

Now let's look at the middle panel above, representing the metabolic milieu resulting from cold exposure without calorie restriction - i.e. eating enough calorie to fully compensate for the extra thermogenesis required, so as to maintain the same (unhealthy) weight as someone eating ad lib. As you can see, to first approximation, things are green (activated) across the board. But activating SIRT1 and AMPK via adiponectin, CE upregulates the same longevity pathway as CR - a good thing. But at the same time, with an excess of calories coming from eating completely ad lib, the Insulin/IGF-1 pathway gets fully activated, and mTOR gets an extra boost from the PKA pathway discussed in [1]. So you get the detrimental, pro-aging effects of Insulin / IGF-1 (systemic inflammation, etc.) along with the mixed blessing of the full complement of anabolic effects of mTOR activation (include white fat synthesis & obesity). As a result, cold exposure combined with an ad lib diet (e.g. Ikeno et al's "cold but chubby" control mice, discussed here), doesn't improve health or longevity relative to warm, ad lib fed controls. In other words, cold ad lib rodents eat a lot more, maintain the same weight, and live as long as, but not longer than, warm ad lib controls.

 

By now you may see where I'm going with this. But if not, take a look at the third panel above, representing the metabolic milieu resulting from the combination of CR & CE. As you can see, CR keeps Insulin & IGF-1 low, preventing their detrimental, pro-aging effects. But at the same time, CE does an "end run" around the Insulin/IGF-1 → AKT → mTOR pathway, instead activating mTOR via the "back door" PKA pathway. Activated in this way, mTOR helps promote growth of important new cells, but in different combination than if activated via the insulin/IGF-1 pathway (e.g. promoting BAT rather than WAT). As a result, the combination of CR + CE provides the anabolic bone, brain and immunity benefits of mTOR activity, without the downsides associated with elevated insulin and IGF-1. 

 

In short, the combination of CR & CE appears to allow you to have your cake and eat it too.

 

Now before Michael or Al jump all over me, let me once again qualify what I've said above. These are crude approximations of the incredibly complex metabolic pathways involved in normal metabolism, and the changes brought about by CR and/or CE. The pathway diagrams are far from complete and I'm not certain they are entirely correct, even as approximations. But as far as I can tell, the model I describe is consistent with both the low level biochemistry and the studies of CR and/or CE outcomes in rodents and people.

 

In the context of the eco-evolutionary explanation I presented in my post from yesterday, a synergy between CR & CE makes a lot of sense. If CR and CE almost always co-occurred in our evolutionary past, the body would naturally become tuned to maximize health/longevity when faced with the two in combination, but not necessarily when one of them occurs without the other. All bets are off when the body is faced with conditions it hasn't encountered repeatedly in the past. This sort of mismatch between genes and environment is evident in the recent obesity epidemic resulting from the combination of unlimited calories and sedentary lifestyle which is common today but which was extremely rare for our ancestors. This sort of mismatch also appears evident (to me anyway) in the disappointing results of studies in which either CR or CE is tested in isolation, as discussed in yesterday's post. It's the combination of the two that's critical for health & longevity based on the rodent and monkey lifespan studies. The above model may (crudely) represent the biochemical explanation of how CR & CE work together to bring about these synergistic benefits. If true, this model would appear to provide renewed hope that CR can provide substantially improved health & longevity, but only when combined it with its natural partner, cold exposure.

 

--Dean

 

-------

[1] J Clin Invest. 2016 Mar 28. pii: 83532. doi: 10.1172/JCI83532. [Epub ahead of print]

 
Activation of mTORC1 is essential for β-adrenergic stimulation of adipose
browning.
 
Liu D, Bordicchia M, Zhang C, Fang H, Wei W, Li JL, Guilherme A, Guntur K, Czech 
MP, Collins S.
 
 
A classic metabolic concept posits that insulin promotes energy storage and
adipose expansion, while catecholamines stimulate release of adipose energy
stores by hydrolysis of triglycerides through β-adrenergic receptor (βARs) and
protein kinase A (PKA) signaling. Here, we have shown that a key hub in the
insulin signaling pathway, activation of p70 ribosomal S6 kinase (S6K1) through
mTORC1, is also triggered by PKA activation in both mouse and human adipocytes.
Mice with mTORC1 impairment, either through adipocyte-specific deletion of Raptor
or pharmacologic rapamycin treatment, were refractory to the well-known
βAR-dependent increase of uncoupling protein UCP1 expression and expansion of
beige/brite adipocytes (so-called browning) in white adipose tissue (WAT).
Mechanistically, PKA directly phosphorylated mTOR and RAPTOR on unique serine
residues, an effect that was independent of insulin/AKT signaling. Abrogation of 
the PKA site within RAPTOR disrupted βAR/mTORC1 activation of S6K1 without
affecting mTORC1 activation by insulin. Conversely, a phosphomimetic RAPTOR
augmented S6K1 activity. Together, these studies reveal a signaling pathway from 
βARs and PKA through mTORC1 that is required for adipose browning by
catecholamines and provides potential therapeutic strategies to enhance energy
expenditure and combat metabolic disease.
 
PMID: 27018708
 

----------------

[2] Diabetes. 2016 Mar 2. pii: db150662. [Epub ahead of print]

 
A synergistic anti-obesity effect by a combination of capsinoids and cold
temperature through promoting beige adipocyte biogenesis.
 
Ohyama K(1), Nogusa Y(2), Shinoda K(3), Suzuki K(2), Bannai M(4), Kajimura S(5).
 
 
Beige adipocytes emerge postnatally within the white adipose tissue (WAT) in
response to certain environmental cues, such as chronic cold exposure. Because of
its highly recruitable nature and relevance to adult humans, beige adipocytes
have gained much attention as an attractive cellular target for anti-obesity
therapy. However, molecular circuits that preferentially promote beige adipocyte 
biogenesis remain poorly understood. Here, we report that a combination of mild
cold exposure at 17°C and capsinoids, a non-pungent analog of capsaicin,
synergistically and preferentially promotes beige adipocyte biogenesis and
ameliorate diet-induced obesity. Gain- and loss-of-function studies show that the
combination of capsinoids and cold exposure synergistically promotes beige
adipocyte development through the β2-adrenoceptor signaling pathway. This
synergistic effect on beige adipocyte biogenesis occurs through an increased
half-life of PRDM16, a dominant transcriptional regulator of brown/beige
adipocyte development. Our observations document a previously unappreciated
molecular circuit that controls beige adipocyte biogenesis and suggest a
plausible approach to increase whole body energy expenditure by combining dietary
components and environmental cues.
 
PMID: 26936964

----------------

[3] Chronobiol Int. 2009 Jul;26(5):838-53. doi: 10.1080/07420520903044281.

 
Daily rhythms of core temperature and locomotor activity indicate different
adaptive strategies to cold exposure in adult and aged mouse lemurs acclimated to
a summer-like photoperiod.
 
Terrien J(1), Zizzari P, Epelbaum J, Perret M, Aujard F.
 
Author information: 
(1)Mecanismes Adaptatifs et Evolution, Brunoy, France. terrien@mnhn.fr
 
Daily variations in core temperature (Tc) within the normothermic range imply
thermoregulatory processes that are essential for optimal function and survival. 
Higher susceptibility towards cold exposure in older animals suggests that these 
processes are disturbed with age. In the mouse lemur, a long-day breeder, we
tested whether aging affected circadian rhythmicity of Tc, locomotor activity
(LA), and energy balance under long-day conditions when exposed to cold. Adult (N
= 7) and aged (N = 5) mouse lemurs acclimated to LD14/10 were exposed to 10-day
periods at 25 and 12 degrees C. Tc and LA rhythms were recorded by telemetry, and
caloric intake (CI), body mass changes, and plasma IGF-1 were measured. During
exposure to 25 degrees C, both adult and aged mouse lemurs exhibited strong daily
variations in Tc. Aged animals exhibited lower levels of nocturnal LA and
nocturnal and diurnal Tc levels in comparison to adults. Body mass and IGF-1
levels remained unchanged with aging. Under cold exposure, torpor bout occurrence
was never observed whatever the age category. Adult and aged mouse lemurs
maintained their Tc in the normothermic range and a positive energy balance. All 
animals exhibited increase in CI and decrease in IGF-1 in response to cold. The
decrease in IGF-1 was delayed in aged mouse lemurs compared to adults. Moreover, 
both adult and aged animals responded to cold exposure by increasing their
diurnal LA compared to those under Ta = 25 degrees C. However, aged animals
exhibited a strong decrease in nocturnal LA and Tc, whereas cold effects were
only slight in adults. The temporal organization and amplitude of the daily phase
of low Tc were particularly well preserved under cold exposure in both age
groups. Sexually active mouse lemurs exposed to cold thus seemed to prevent
torpor exhibition and temporal disorganization of daily rhythms of Tc, even
during aging. However, although energy balance was not impaired with age in mouse
lemurs after cold exposure, aging was associated with lower LA and Tc during the 
night and delayed decrease in IGF-1. This might reflect that adaptive strategies 
to cold exposure differ with age in mouse lemurs acclimated to a summer-like
photoperiod.
 
PMID: 19637046
 
----------
[4] PLoS One. 2015 Jun 19;10(6):e0130627. doi: 10.1371/journal.pone.0130627.
eCollection 2015.

mTORC1 Signaling Promotes Osteoblast Differentiation from Preosteoblasts.

Chen J(1), Long F(2).
 
Free full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4474698/

Preosteoblasts are precursor cells that are committed to the osteoblast lineage.
Differentiation of these cells to mature osteoblasts is regulated by the
extracellular factors and environmental cues. Recent studies have implicated mTOR
signaling in the regulation of osteoblast differentiation. However, mTOR exists
in two distinct protein complexes (mTORC1 and mTORC2), and the specific role of
mTORC1 in regulating the progression of preosteoblasts to mature osteoblastis
still unclear. In this study, we first deleted Raptor, a unique and essential
component of mTORC1, in primary calvarial cells. Deletion of Raptor resulted in
loss of mTORC1 but an increase in mTORC2 signaling without overtly affecting
autophagy. Under the osteogenic culture condition, Raptor-deficient cells
exhibited a decrease in matrix synthesis and mineralization. qPCR analyses
revealed that deletion of Raptor reduced the expression of late-stage markers for
osteoblast differentiation (Bglap, Ibsp, and Col1a), while slightly increasing
early osteoblast markers (Runx2, Sp7, and Alpl). Consistent with the findings in
vitro, genetic ablation of Raptor in osterix-expressing cells led to osteopenia
in mice. Together, our findings have identified a specific role for mTORC1 in the
transition from preosteoblasts to mature osteoblasts.


PMCID: PMC4474698
PMID: 26090674
 
--------
[5] Nature. 2013 Jul 25;499(7459):485-90. doi: 10.1038/nature12297. Epub 2013 Jun 30.
 
mTORC1 couples immune signals and metabolic programming to establish T(reg)-cell 
function.
 
Zeng H(1), Yang K, Cloer C, Neale G, Vogel P, Chi H.
 
 
The mechanistic target of rapamycin (mTOR) pathway integrates diverse
environmental inputs, including immune signals and metabolic cues, to direct
T-cell fate decisions. The activation of mTOR, which is the catalytic subunit of 
the mTORC1 and mTORC2 complexes, delivers an obligatory signal for the proper
activation and differentiation of effector CD4(+) T cells, whereas in the
regulatory T-cell (T(reg)) compartment, the Akt-mTOR axis is widely acknowledged 
as a crucial negative regulator of T(reg)-cell de novo differentiation and
population expansion. However, whether mTOR signalling affects the homeostasis
and function of T(reg) cells remains largely unexplored. Here we show that mTORC1
signalling is a pivotal positive determinant of T(reg)-cell function in mice.
T(reg) cells have elevated steady-state mTORC1 activity compared to naive T
cells. Signals through the T-cell antigen receptor (TCR) and interleukin-2 (IL-2)
provide major inputs for mTORC1 activation, which in turn programs the
suppressive function of T(reg) cells. Disruption of mTORC1 through Treg-specific 
deletion of the essential component raptor leads to a profound loss of
T(reg)-cell suppressive activity in vivo and the development of a fatal early
onset inflammatory disorder. Mechanistically, raptor/mTORC1 signalling in T(reg) 
cells promotes cholesterol and lipid metabolism, with the mevalonate pathway
particularly important for coordinating T(reg)-cell proliferation and
upregulation of the suppressive molecules CTLA4 and ICOS to establish Treg-cell
functional competency. By contrast, mTORC1 does not directly affect the
expression of Foxp3 or anti- and pro-inflammatory cytokines in T(reg) cells,
suggesting a non-conventional mechanism for T(reg)-cell functional regulation.
Finally, we provide evidence that mTORC1 maintains T(reg)-cell function partly
through inhibiting the mTORC2 pathway. Our results demonstrate that mTORC1 acts
as a fundamental 'rheostat' in T(reg) cells to link immunological signals from
TCR and IL-2 to lipogenic pathways and functional fitness, and highlight a
central role of metabolic programming of T(reg)-cell suppressive activity in
immune homeostasis and tolerance.
 
PMCID: PMC3759242
PMID: 23812589
 
---------
[6] J Immunol. 2014 Nov 1;193(9):4477-84. doi: 10.4049/jimmunol.1401558. Epub 2014

Sep 26.

mTORC1-dependent metabolic reprogramming is a prerequisite for NK cell effector
function.

Donnelly RP(1), Loftus RM(1), Keating SE(1), Liou KT(2), Biron CA(2), Gardiner
CM(1), Finlay DK(3).

Free full text: http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/25261477/

The mammalian target of rapamycin complex 1 (mTORC1) is a key regulator of
cellular metabolism and also has fundamental roles in controlling immune
responses. Emerging evidence suggests that these two functions of mTORC1 are
integrally linked. However, little is known regarding mTORC1 function in
controlling the metabolism and function of NK cells, lymphocytes that play key
roles in antiviral and antitumor immunity. This study investigated the hypothesis
that mTORC1-controlled metabolism underpins normal NK cell proinflammatory
function. We demonstrate that mTORC1 is robustly stimulated in NK cells activated
in vivo and in vitro. This mTORC1 activity is required for the production of the
key NK cell effector molecules IFN-γ, which is important in delivering
antimicrobial and immunoregulatory functions, and granzyme B, a critical
component of NK cell cytotoxic granules. The data reveal that NK cells undergo
dramatic metabolic reprogramming upon activation, upregulating rates of glucose
uptake and glycolysis, and that mTORC1 activity is essential for attaining this
elevated glycolytic state. Directly limiting the rate of glycolysis is sufficient
to inhibit IFN-γ production and granzyme B expression. This study provides the
highly novel insight that mTORC1-mediated metabolic reprogramming of

NK cells is a prerequisite for the acquisition of normal effector functions.

Copyright © 2014 by The American Association of Immunologists, Inc.

PMCID: PMC4201970
PMID: 25261477

 

------------

[7] J Neurosci. 2012 Oct 24;32(43):15012-26. doi: 10.1523/JNEUROSCI.2248-12.2012.

 
Mammalian target of rapamycin signaling is a key regulator of the
transit-amplifying progenitor pool in the adult and aging forebrain.
 
Paliouras GN(1), Hamilton LK, Aumont A, Joppé SE, Barnabé-Heider F, Fernandes KJ.
 
 
Adult forebrain neurogenesis is dynamically regulated. Multiple families of
niche-derived cues have been implicated in this regulation, but the precise roles
of key intracellular signaling pathways remain vaguely defined. Here, we show
that mammalian target of rapamycin (mTOR) signaling is pivotal in determining
proliferation versus quiescence in the adult forebrain neural stem cell (NSC)
niche. Within this niche, mTOR complex-1 (mTORC1) activation displays stage
specificity, occurring in transiently amplifying (TA) progenitor cells but not in
GFAP+ stem cells. Inhibiting mTORC1 depletes the TA progenitor pool in vivo and
suppresses epidermal growth factor (EGF)-induced proliferation within neurosphere
cultures. Interestingly, mTORC1 inhibition induces a quiescence-like phenotype
that is reversible. Likewise, mTORC1 activity and progenitor proliferation
decline within the quiescent NSC niche of the aging brain, while EGF
administration reactivates the quiescent niche in an mTORC1-dependent manner.
These findings establish fundamental links between mTOR signaling, proliferation,
and aging-associated quiescence in the adult forebrain NSC niche.
 
PMID: 23100423
 
-----------
[8] Rev Physiol Biochem Pharmacol. 2014;166:43-95. doi: 10.1007/112_2013_17.
 
The role of mTORC1 in regulating protein synthesis and skeletal muscle mass in
response to various mechanical stimuli.
 
Goodman CA(1).
 
Author information: 
(1)Department of Comparative Biosciences, School of Veterinary Medicine,
University of Wisconsin-Madison, 2015 Linden Drive, Madison, WI, 53706, USA,
cgoodman2@wisc.edu.
 
Skeletal muscle plays a fundamental role in mobility, disease prevention, and
quality of life. Skeletal muscle mass is, in part, determined by the rates of
protein synthesis, and mechanical loading is a major regulator of protein
synthesis and skeletal muscle mass. The mammalian/mechanistic target of rapamycin
(mTOR), found in the multi-protein complex, mTORC1, is proposed to play an
essential role in the regulation of protein synthesis and skeletal muscle mass.
The purpose of this review is to examine the function of mTORC1 in relation to
protein synthesis and cell growth, the current evidence from rodent and human
studies for the activation of mTORC1 signaling by different types of mechanical
stimuli, whether mTORC1 signaling is necessary for changes in protein synthesis
and skeletal muscle mass that occur in response to different types of mechanical 
stimuli, and the proposed molecular signaling mechanisms that may be responsible 
for the mechanical activation of mTORC1 signaling.
 
PMID: 24442322

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My parents protected me from hunger and kept me from cold.  For health, they pushed meal times ("dinner time") and warm clothing ("go back and at least grab a hat").  Ironically, fewer dinners and fewer hats may be back.  If I were an icon, it could be the thin / cool Snow Miser https://www.youtube.com/watch?v=8mw-1ehsuJM ha!

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Thanks Deans, but I suppose the folks in the below papers were not living in a germ-free lab either.

 

 

White blood cell count as a predictor of mortality: results over 18 years from the Normative Aging Study.
de Labry LO, Campion EW, Glynn RJ, Vokonas PS.
J Clin Epidemiol. 1990;43(2):153-7.
PMID: 2303845
 
Abstract
 
The ubiquitous white blood cell count (WBC) has rarely been analyzed as a predictor of future mortality. We examined WBC measured in prospective examinations of 2011 initially healthy men in the Normative Aging Study (mean age 47.5), followed for an average of 13.6 years with 27,402 man-years of observation. Between 1970 and 1987, 183 participants died. Mortality rates for men with baseline WBC over 9000 were 12.2/1000 man-years, 1.8-2.5 times those of men with lower WBC in each of three age groups. Proportional hazards models controlling for established risk factors including age, systolic blood pressure, cholesterol and smoking status, found WBC at the baseline exam to be an independent predictor of mortality over the following years. Even within the normal range, a difference of 1000 in the initial WBC increased the risk ratio by 1.2 (95% CI 1.1, 1.3). The relation of initial WBC to mortality was not affected by baseline age, body mass index (BMI), smoking or blood pressure. These findings are not explained by medication effects. We conclude that the WBC is an independent predictor of all-cause mortality.
 
 
White blood cell count and risk for all-cause, cardiovascular, and cancer mortality in a cohort of Koreans.
Jee SH, Park JY, Kim HS, Lee TY, Samet JM.
Am J Epidemiol. 2005 Dec 1;162(11):1062-9. Epub 2005 Oct 12.
PMID: 16221804 Free Article
 
Abstract
 
The authors conducted a 10-year prospective cohort study of mortality in relation to white blood cell counts of 437,454 Koreans, aged 40-95 years, who received health insurance from the National Health Insurance Corporation and were medically evaluated in 1993 or 1995, with white blood cell measurement. The main outcome measures were mortality from all causes, all cancers, and all atherosclerotic cardiovascular diseases (ASCVD). Hazard ratios and 95% confidence intervals were calculated using Cox proportional hazards models with adjustment for age and potential confounders. During follow-up, 48,757 deaths occurred, with 15,507 deaths from cancer and 11,676 from ASCVD. For men and women, white blood cell count was associated with all-cause mortality and ASCVD mortality but not with cancer mortality. In healthy nonsmokers, a graded association between a higher white blood cell count and a higher risk of ASCVD was observed in men (highest vs. lowest quintile: hazard ratio = 2.10, 95% confidence interval: 1.50, 2.94) and in women (hazard ratio = 1.35, 95% confidence interval: 1.17, 1.56). In healthy smokers, a graded association between a higher white blood cell count and a higher risk of ASCVD was also observed in men (highest vs. lowest quintile: hazard ratio = 1.46, 95% confidence interval: 1.25, 1.72). These findings indicate that the white blood cell count is an independent risk factor for all-cause mortality and for ASCVD mortality.

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What Is the Optimal White Blood Cell (WBC) Count for Health & Longevity?

 

Al wrote:

Thanks Deans, but I suppose the folks in the below papers were not living in a germ-free lab either.

 

Of course you are right Al. The people in the two studies you posted (PMIDs 2303845 and 16221804) were indeed not living in a germ-free lab. That's why I'm wondering if you actually read the papers you pointed to, rather than just the abstracts. If you had, I don't think you could help but have noticed that the details of both papers undermine your apparent perspective (which appears to be something like "when it comes to WBC count, the lower the better for health and longevity") and vindicate my own, which I would characterize as "elevated WBC is a sign of systemic inflammation and should be avoided, but at the same time it is quite possible to have too low a WBC for optimal health and longevity by making it difficult to fight off cancer and infections."
 
I'll speak to your two papers in turn, and then add a couple more of my own for emphasis .
 
Your first paper, PMID 2303845, is a study of 2000 middle aged men in which they compared baseline WBC count (which I'll abbreviate as simply WBC in the remainder) with subsequent mortality over a 14 year follow-up period during which about 10% (~200) of them died. Here is the key table from the full text of the paper, in which I've highlighted a couple key elements:
 
NIUdRkr.png
 
The first thing to notice is that their lowest quartile for WBC (the top row of the table) has a cutoff threshold of 5000 white blood cells per ml of blood. You do realize that by this criteria both you and I would fall into their lowest category, even with my recently "elevated" WBC of value of 4.5 which, by the author's scale, equates to 4500 WBCs / ml ? So much for cold exposure pushing my WBC into dangerously elevated territory...
 
But there's more. Notices the three cells I've highlighted in green. They represent the relatively younger, presumably healthier participates in the study whose WBC was higher than the people in the lowest quartile. Notice their mortality? They were less likely to die during the follow-up period than people of corresponding ages with the lowest WBC. So much for "lower WBC is always better". The authors come right out and say exactly this:
 
That the WBC relates to immediate prognosis in acute illness is beyond dispute. The curve is
U-shaped. Mortality associated with leukopenia [low WBCs - DP]  reflects the effects of hematologic
malignancies, immunologic disorders or immunosuppression by medication, as well as to bone marrow
suppression from severe illness, myelophthisis or overwhelming infection.
 
I think a pretty good argument can be made that this study not only fails to support your premise that "lower WBC is always better", it clearly refutes it. In fact, I think a strong case could be made that if you are young, either chronologically or biologically (like virtually all of us are here), this data suggests being in the second quartile of WBC (5000-7000) would be advantageous from an all-cause mortality perspective. Certainly being in the 5000-7000 range doesn't look like it would be detrimental, particularly if you're living a healthy lifestyle and eating a good diet, which you can be sure very few of the veterans followed in this study were doing during the mid-1960s and 70s when this study was conducted. The authors say mortality from leukopenia can reflect the effects of several things, including "immunosuppression by medication". I would add to that "or immunosuppression by severe dietary restriction", per this discussion of the increased mortality from infections that can result from the immunosuppressive effects of CR. The severely-restricted and cold-exposed Ikeno mice (discussed here), who avoided cancer and other causes of death only to die of pneumonia, are a likely additional example of the downsides of having an immune system that is too 'quiescent' (i.e. suppressed) to do its job when required. More on that below.
 
But first, on to your second paper, PMID 16221804. Here they studied a much larger group Korean men and women (nearly 1/2 million) for 10 years to observe the association between WBC and mortality. The first interesting thing to look at are the baseline characteristics of the participants, segmented by WBC levels:
 
C1EeMln.png
 
The authors of this study once again chose to use the same WBC threshold as your other study, namely < 5.0 (i.e. < 5000 WBCs / ml) for the lowest WBC category. So once again we both would fall into the lowest WBC category, even with my current "elevated" level of 4.5. The next thing to note is the comparison between the baseline demographics and lifestyle characteristics of subjects and their relationship to WBC status. In short, there is a clear positive correlation between having higher WBC and each of the following: obesity, high cholesterol, high blood pressure, diabetes, cigarette smoking, alcohol intake and lack of exercise. With all these lifestyle strikes against them, it's little wonder why the bodies of the high WBC folks were inflamed, and that they were more likely to die, although the authors did try to statistically correct for these health and lifestyle factors. I wouldn't call them "confounding factors" since they are likely the start of the causal pathway that goes poor diet/lifestyle → inflammation ≈ high WBC → mortality.
 
Note the one baseline demographic parameter that was inversely related to WBC was age. The subjects with low WBC were more likely to be elderly than young. This almost certainly reflects is the well-known drop in immunocompetence as people get older, with the concomitant drop in ability to fighting off invaders, both foreign (viruses and bacteria) and domestic (cancer). The question in my mind is why we CR folks would want to hurry the process along by further suppressing our immune system through a severely restricted diet, when we know now how it can be avoided... An inflamed body is a bad thing, but an immune system that has been suppressed by lack of resources to the point where it can't do its job when it's need bad too...
 
But let's look at their mortality data to see what's really going on:
 
Vxghqvi.png
 
Notice for death from all causes (yellow highlights), it's only for WBCs above 7.0 where there is even a trend towards increased mortality, and only above 8.0 that that trend becomes significant. Another strike against the idea that you've got to have very low WBC to minimize risk of dying... 
 
Notice for deaths from cancer (green highlights), having the lowest WBC at baseline was associated with higher mortality (albeit weakly). Whether this reflects immunosuppression due to latent cancer, or simply an immune system less capable of killing off cancer cells when they later develop, is impossible to tell. But in either case we see for deadly conditions requiring the immune system to do it's job of killing off invaders, having low WBC is definitely not where you want to be, according to this data. It's almost certain that if they had broken out "pneumonia and other infections" as a cause of death, the increased mortality risk for those with a low WBC would have been much more dramatic than the modest increase seen with cancer.
 
It was only for cardiovascular disease mortality that there was a strong linear trend towards increased mortality with increasing WBC. Interestingly, the trend was much weaker in women (not shown), where only a WBC above 6.0 was associated with an increased risk of CVD mortality.  Still, if you concerned about having a heart attack, it might be wise to keep WBC in the first sextile (< 5.0), like you and both have Al. But even for CVD, I suspect that elevated WBC at baseline may have been an indicator of systemic inflammation due to a poor diet & lifestyle that would later blossom into full-blown metabolic syndrome and death from cardiovascular disease among these initially "healthy" subjects.
 
In short, I've never suggested that having a high WBC is a good idea. Your two studies bear that out, although I'm actually a bit surprised at how weak and J-shaped (in PMID 2303845) the correlation between WBC and all-cause mortality actually appears to be, especially among otherwise "healthy" people.
 
Recall my argument is that while you can certainly have too high WBC, you can also have too low WBC for optimal health & longevity, particularly when it comes to fighting off infections when the proverbial sh*t hits the fan, and the chips are down. To illustrate this consider the following two studies. 
 
First, study [1] followed 14K people for 30 days after they visited one of 186 Pennsylvania hospitals (go PA!) and were discharged with a diagnosis of pulmonary embolism (PE). I wouldn't normally post studies where the subjects were sick individuals, since they generally aren't representative of healthy CRers. But in this case, that is exactly the point. We want to look at what happens when the chips are down, you've gotten sick or injured, and now you're trying to recover. Is it better to have low WBC or high WBC?
 
Not surprisingly (to me anyway)  the people with the lowest WBC (< 5.0) were twice as likely to die (relative to folks with a much higher WBC of 8.0 - 10.0) while trying to recover in the 30 days following an embolism. And remember, these folks were judged well enough to be discharged and go home. Nevertheless, 11% of those with the lowest WBC died during the subsequent 30 days, a good fraction of them likely from infections they were unable to fight off.
 
But here is the icing on the cake, or nail in the coffin, depending on how you look at it, from study [2]:
 
NAC1Xrp.png
 
It represents the percent of heart attack suffers (from among nearly 200,000 who were tracked in the study) who died while in the hospital recovering from their AMI (acute myocardial infarction). That data is so J-shaped I'd characterize it as U-shaped. Notice that people with a WBC in the 2-3 range (where you and other CRers fall, as did I before cold exposure), had a 20% risk of dying while in the hospital for a few days to a couple weeks while trying to recover. Their risk of croaking in the hospital was 4x higher than that of people with WBC even just a little bit higher, like mine is now in the 4-5 range. In fact, the risk for people in the 2-3 WBC range was as high as people at the other extreme, with such high systemic inflammation that their WBC was above 20. The nadir of mortality risk was actually a little bit higher than mine is now - in the range of 5-6 as can be seen in the above graph. Those folks appear to enjoy a hospital mortality risk of only ~3-4%, which is around 6x lower than the ~20% mortality risk of people with very low WBC counts, like many CRers.
 
Here is one more [3], thanks to Mike Lustgarten. It is from the Baltimore Longitudinal Study of Aging, which followed 1700 initially healthy men from 1958 through 2002. If found:
 
The WBC count was nonlinearly associated with all-cause mortality and almost linearly associated with
cardiovascular mortality. Participants with baseline WBC <3,500 cells/mm3 and WBC >6,000 cells/mm3 had
higher mortality than those with 3,500 to 6,000 WBC/mm3.
 
Again we see a WBC "sweet spot" above 3.5 and below 6.0. Here is the relevant graph from the full text of [3], showing the correlation of WBC (x-axis) with mortality (y-axis) from all-causes (top), CVD (middle) and cancer (bottom):
 
pEMf42n.png
 
As is apparent in the top graph, the sweet spot for all-cause mortality appears to be almost exactly 4.5. Where have I heard that number before? Gotta love it when it works out like that.
 
In summary, as I've been saying, having an inflamed body as reflected by an elevated WBC (e.g. > 8.0), is a bad thing. But having a WBC which is too low (e.g. < 4.0) can also be a bad thing, because it makes it harder to recover from illness or injury, fight off infections, and/or kill off cancer cells.
 
I hope after this post I won't have to keep beating a dead horse on this point. And just a reminder given the topic of this thread, one way to boost immunocompetence without risking increased inflammation is cold exposure, as discussed in this post.
 
--Dean
 
------
[1]  Am J Hematol. 2013 Aug;88(8):677-81. doi: 10.1002/ajh.23484. Epub 2013 Jun 20.
 
White blood cell count and mortality in patients with acute pulmonary embolism.
 
Venetz C(1), Labarère J, Jiménez D, Aujesky D.
 
 
Although associated with adverse outcomes in other cardiovascular diseases, the
prognostic value of an elevated white blood cell (WBC) count, a marker of
inflammation and hypercoagulability, is uncertain in patients with pulmonary
embolism (PE). We therefore sought to assess the prognostic impact of the WBC in 
a large, state-wide retrospective cohort of patients with PE. We evaluated 14,228
patient discharges with a primary diagnosis of PE from 186 hospitals in
Pennsylvania. We used random-intercept logistic regression to assess the
independent association between WBC count levels at the time of presentation and 
mortality and hospital readmission within 30 days, adjusting for patient and
hospital characteristics. Patients with an admission WBC count <5.0, 5.0-7.8,
7.9-9.8, 9.9-12.6, and >12.6 × 10(9) /L had a cumulative 30-day mortality of
10.9%, 6.2%, 5.4%, 8.3%, and 16.3% (P < 0.001), and a readmission rate of 17.6%, 
11.9%, 10.9%, 11.5%, and 15.0%, respectively (P < 0.001). Compared with patients 
with a WBC count 7.9-9.8 × 10(9) /L, adjusted odds of 30-day mortality were
significantly greater for patients with a WBC count <5.0 × 10(9) /L (odds ratio
[OR] 1.52, 95% confidence interval [CI] 1.14-2.03), 9.9-12.6 × 10(9) /L (OR 1.55,
95% CI 1.26-1.91), or >12.6 × 10(9) /L (OR 2.22, 95% CI 1.83-2.69), respectively.
The adjusted odds of readmission were also significantly increased for patients
with a WBC count <5.0 × 10(9) /L (OR 1.34, 95% CI 1.07-1.68) or >12.6 × 10(9) /L 
(OR 1.29, 95% CI 1.10-1.51). In patients presenting with PE, WBC count is an
independent predictor of short-term mortality and hospital readmission.
 
Copyright © 2013 Wiley Periodicals, Inc.
 
PMID: 23674436
 
 ----------------
[2] Acad Emerg Med. 2004 Oct;11(10):1049-60.
 
The association between white blood cell count and acute myocardial infarction
in-hospital mortality: findings from the National Registry of Myocardial
Infarction.
 
Grzybowski M(1), Welch RD, Parsons L, Ndumele CE, Chen E, Zalenski R, Barron HV.
 
Author information: 
(1)Department of Emergency Medicine, Wayne State University School of Medicine,
6G University Health Center, 4201 St. Antoine, Detroit, MI 48201, USA.
mgrzyb@med.wayne.edu.
 
OBJECTIVES: Although cross-sectional and prospective studies have shown that the 
white blood cell (WBC) count is associated with long-term mortality for patients 
with ischemic heart disease, the role of the WBC count as an independent
predictor of short-term mortality in patients with acute myocardial infarction
(AMI) has not been examined as extensively. The objective of this study was to
determine whether the WBC count is associated with in-hospital mortality for
patients with ischemic heart disease after controlling for potential confounders.
METHODS: From July 31, 2000, to July 31, 2001, the National Registry of
Myocardial Infarction 4 enrolled 186,727 AMI patients. A total of 115,273
patients were included in the analysis.
RESULTS: WBC counts were subdivided into intervals of 1,000/mL, and in-hospital
mortality rates were determined for each interval. The distribution revealed a
J-shaped curve. Patients with WBC counts >5,000/mL were subdivided into
quartiles, whereas patients with WBC counts <5,000/mL were assigned to a separate
category labeled "subquartile" and were analyzed separately. A linear increase in
in-hospital mortality by WBC count quartile was found. The unadjusted odds ratio 
(OR) for the fourth versus the first quartile showed strong associations with
in-hospital mortality among the entire population and by gender: 4.09 (95%
confidence interval [95% CI] = 3.83 to 4.73) for all patients, 4.31 (95% CI =
3.93 to 4.73) for men, and 3.65 (95% CI = 3.32 to 4.01) for women. Following
adjustment for covariates, the magnitude of the ORs attenuated, but the ORs
remained highly significant (OR, 2.71 [95% CI = 2.53 to 2.90] for all patients;
OR, 2.87 [95% CI = 2.59 to 3.19] for men; OR, 2.61 [95% CI = 2.36 to 2.99] for
women). Reperfused patients had consistently lower in-hospital mortality rates
for all patients and by gender (p < 0.0001).
CONCLUSIONS: The WBC count is an independent predictor of in-hospital AMI
mortality and may be useful in assessing the prognosis of AMI in conjunction with
other early risk-stratification factors. Whether elevated WBC count is a marker
of the inflammatory process or is a direct risk factor for AMI remains unclear.
Given the simplicity and availability of the WBC count, the authors conclude that
the WBC count should be used in conjunction with other ancillary tests to assess 
the prognosis of a patient with AMI.
 
PMID: 15466147
 
--------
[3] J Am Coll Cardiol. 2007 May 8;49(18):1841-50. Epub 2007 Apr 23.
 
White blood cell count and mortality in the Baltimore Longitudinal Study of
Aging.
 
Ruggiero C(1), Metter EJ, Cherubini A, Maggio M, Sen R, Najjar SS, Windham GB,
Ble A, Senin U, Ferrucci L.
 
 
Comment in
    J Am Coll Cardiol. 2007 Oct 30;50(18):1810; author reply 1810-1.
 
OBJECTIVES: We investigated the secular trend in white blood cell (WBC) count and
the relationship between WBC count and mortality between 1958 and 2002.
BACKGROUND: The WBC count is a clinical marker of inflammation and a strong
predictor of mortality. Limited data exist on the WBC count secular trend and the
relationship between WBC and mortality.
METHODS: One thousand eighty-three women and 1,720 men were evaluated
longitudinally in the Baltimore Longitudinal Study of Aging. Blood samples and
medical information were collected at the study entry and every 2 years during
follow-up visits. The WBC count and all-cause, cardiovascular, and cancer
mortality were assessed.
RESULTS: A downward trend in WBC count was observed from 1958 to 2002. The
secular downward trend was independent of age, gender, race, smoking, body mass
index, and physical activity. The WBC count was nonlinearly associated with
all-cause mortality and almost linearly associated with cardiovascular mortality.
Participants with baseline WBC <3,500 cells/mm3 and WBC >6,000 cells/mm3 had
higher mortality than those with 3,500 to 6,000 WBC/mm3. Within each WBC group,
age-adjusted mortality rates declined in successive cohorts from the 1960s to the
1990s. Participants who died had higher WBC than those who survived, and the
difference was statistically significant within 5 years before death.
CONCLUSIONS: Our study provides evidence for a secular downward trend in WBC
count over the period from 1958 to 2002. Higher WBC counts are associated with
higher mortality in successive cohorts. We found no evidence that the decline of 
age-specific mortality rates that occurred from 1960 to 2000 was attributable to 
a secular downward trend in WBC.
 
PMCID: PMC2646088
PMID: 17481443

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Dean,

 

The papers that I provided of healthy subjects said that WBC counts related positively with mortality.  I agree was this not significant blip of not significantly lower mortality for the Koreans, whom we are not, at the lower end of the WBC counts, but the authors still conclude that there is increasing mortality across the cell counts spectrum.

 

Re many other papers  on the issue: Unhealthy people are not what we should emulate.  

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Al,

Unhealthy people are not what we should emulate.  

 

Agreed. We should neither emulate nor try to learn from the results of unhealthy people, since their results often are not very relevant - including the papers you've posted trying to show "lower WBC is better" based on unhealthy people with inflamed bodies and high WBC counts.

 

We should focus on the science relevant to CR. In this case that means the scientific evidence relating to having "low" vs. "very low" WBC counts. Here the science is quite clear - "low" is better than "very low". 

 

More generally, the CR-relevant science shows that CR, at least on its own, can be a mixed blessing.

 

--Dean

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The Perils for Too Little mTOR - Glucocorticoids Reduce Brown Fat and Muscle Mass, Promote Obesity by Deactivating mTOR

 

Here is the press release for a new study to be presented at the Endocrine Society Annual meeting going on this week, thanks once again to my shy CR friend who refuses to post. Sadly, this one hits close to home, but is worth posting about nonetheless.

 

Background: There is a certain class of steroids called glucocorticoids otherwise known as corticosteroids (not to be confused with other, anabolic steroids used by bodybuilders) which have long been known to cause obesity in patients who take them.

 

In this new study, researchers determined the way glucocorticoids cause weight gain is by reducing / deactivating brown fat and (therefore) suppressing thermogenesis, leaving more calories unspent, to be shunted instead into storage as white fat (WAT). Here are a couple relevant passages from the press release describing the study and its results:

 

Their study involved 13 healthy young adults--six men and seven women--with an average age of 28 years. The researchers allocated the participants, in random order, to one week of treatment with prednisolone (15 milligrams per day) and one week of placebo, a dummy drug, separated by a two-week treatment-free period.

 

At the end of each treatment, participants moved to an air-conditioned room cooled to 66.2°F (19°C). There they underwent nuclear medicine scanning with positron emission tomography-computed tomography (PET-CT) of their head and chest as well as measurement of the skin temperature at the base of the neck, where brown fat is located, using a sensitive infrared thermal camera. This technique provided a precise measurement of heat production from brown fat, according to Ho.
 
The subjects also had their oxygen consumption measured in their breath via indirect calorimetry before and after eating a standardized meal. Ho said this is an estimate of how much energy a person produces from absorbed food, which traditionally is referred to as diet-induced thermogenesis.
 
Compared with placebo treatment, prednisolone suppressed uptake of radioactive glucose on PET-CT scanning, reduced heat production in brown fat and increased the production of energy derived from a meal, Ho said. The latter result, he explained, indicated that prednisolone could be enhancing conversion of energy from a meal into stored "bad" [white - DP] fat while not allowing brown fat to do its work of turning energy into heat.

 

So there you have it, a new way to sap yourself of BAT and gain weight - take a round of glucocorticoids/corticosteroids.

 

Sadly, I'm all too familiar with this effect, having watched the changes to my son Kyle's body while being treated for his brain cancer with another glucocorticoid called dexamethasone (DEX). DEX worked wonders to bring down the inflammation that resulted from Kyle's immune system trying to battle his cancer, and relieved the terrible headaches he was getting as a result of the inflammation. The DEX made him constantly hungry which wasn't so bad - he loved to eat. But the DEX took a terrible toll on his body. He was able to maintain his weight by eating a lot, but we watched him go from a strong and muscular 17-year old young man to a weak and flabby young man in the course of just a few months on DEX. In fact, his oncologist said it was her goal to wean Kyle from DEX as soon as possible by replacing it with other treatments, since it was reducing his body's own ability to fight the cancer by suppressing his immune system, was causing his muscles to waste away, and would have prevented him from participating in the clinical trial she was conducting, due to his suppressed immune system. The trial (which he eventually participated in) used immunotherapy to fight the cancer by boosting the body's own immune system. To have a hope of being effective, the experimental treatment (and immunotherapy in general) requires a functioning immune system, so all participants had to be weaned from all glucocorticoid, including DEX and have a white blood cell count above a minimum threshold - something Al and I were talking about...

 

Now I know how and why DEX trashed his immune system and caused him to lose muscle mass, based on [1]. Ironically it turns out to be highly relevant to this thread, and in particular my recent post about CR & CE metabolic pathways. In [1], the researchers fed DEX to rats, and found, in a nutshell, that DEX suppressed protein synthesis in muscle cells by turning off mTOR, causing the classic muscle wasting associated with glucocorticoid which I observed first-hand with Kyle.

 

And it's not just obscure glucocorticoids that negatively impact muscles by turning off mTOR.

 

It appears from [2] that the most frequent side effect of statins, namely muscle weakness and pain, is similarly a result of deactivating mTOR via the Insulin/IGF-1 → AKT → mTOR pathway I discussed yesterday. The title pretty much says it all The AKT/mTOR signaling pathway plays a key role in statin-induced myotoxicity. Myotoxicity means "toxic to muscles". The researchers observed reduced protein synthesis, "accelerated myofibrillar degradation and atrophy of C2C12 myotubes" and increased apoptosis in both isolated mice muscle cells exposed to statins and in mice fed statins orally for 3 weeks. 

 

Pretty scary stuff, particularly since they are starting to talk about putting statins in the drinking water1 based on recent studies of statin benefits in people at supposedly "intermediate risk" of cardiovascular disease, defined as:

 

... 37.9% of the entire [study] population had hypertension and the overall mean BP was 138.1/91.9 mm Hg. The mean total cholesterol level was 201.4 mg/dL and mean LDL-cholesterol level was 127.8 mg/dL.

 

The authors say in the press release: 

 

Overall, in an intermediate-risk population, it appears that everybody benefits from statins and that statins are safe.

 

Very troubling - what he fails to mention in the interview is the side effects of statins observed in many studies, including his own as detailed here:

 

Although fewer members of the active-treatment group had CV-related hospitalizations vs the placebo group (4.4% vs 5.8%, P<0.001), they had significantly higher rates of cataract surgery (3.8% vs 3.1%, P=0.02) and more reports of muscle symptoms (5.8% vs 4.7%, P=0.005). 

 

So the obvious takeaway is to avoid statins if you want to preserve muscle health and avoid glucocorticoids/corticosteroids to preserve both muscle health and immune system function.

 

The more specific insight relevant to this thread is that these studies illustrate how suppressing mTOR (as CR does) can be bad news for the health of one's muscles and immune system, as discussed in my pathways post. The good news I discussed in that post is that it seems that cold exposure, in combination with CR, can turn on mTOR via a different (less detrimental) pathway than the one involving Insulin/IGF-1, thereby helping to avoid the immune system suppression and muscle catabolism that typically accompanies serious CR.

 

--Dean

 

1Just kidding about the drinking water thing - I hope... All the same, between statins, Flint and fluoride, I'm going to continue using my countertop water distiller to replenish my precious bodily fluids.

 

----------

[1] J Biol Chem. 2006 Dec 22;281(51):39128-34. Epub 2006 Oct 30.

 
Dexamethasone represses signaling through the mammalian target of rapamycin in
muscle cells by enhancing expression of REDD1.
 
Wang H(1), Kubica N, Ellisen LW, Jefferson LS, Kimball SR.
 
 
The mammalian target of rapamycin (mTOR), a critical modulator of cell growth,
acts to integrate signals from hormones, nutrients, and growth-promoting stimuli 
to downstream effector mechanisms involved in the regulation of protein
synthesis. Dexamethasone, a synthetic glucocorticoid that represses protein
synthesis, acts to inhibit mTOR signaling as assessed by reduced phosphorylation 
of the downstream targets S6K1 and 4E-BP1. Dexamethasone has also been shown in
one study to up-regulate the expression of REDD1 (also referred to RTP801, a
novel stress-induced gene linked to repression of mTOR signaling) in lymphoid,
but not nonlymphoid, cells. In contrast to the findings of that study, here we
demonstrate that REDD1, but not REDD2, mRNA expression is dramatically induced
following acute dexamethasone treatment both in rat skeletal muscle in vivo and
in L6 myoblasts in culture. In L6 myoblasts, the effect of the drug on mTOR
signaling is efficiently blunted in the presence of REDD1 RNA interference
oligonucleotides. Moreover, the dexamethasone-induced assembly of the mTOR
regulatory complex Tuberin. Hamartin is disrupted in L6 myoblasts following small
interfering RNA-mediated repression of REDD1 expression. Finally, overexpression 
of Rheb, a downstream target of Tuberin function and a positive upstream effector
of mTOR, reverses the effect of dexamethasone on phosphorylation of mTOR
substrates. Overall, the data support the conclusion that REDD1 functions
upstream of Tuberin and Rheb to down-regulate mTOR signaling in response to
dexamethasone.
 
PMID: 17074751
 

-------------

[2] Biochim Biophys Acta. 2015 Aug;1853(8):1841-9. doi: 10.1016/j.bbamcr.2015.04.010.

Epub 2015 Apr 23.
 
The AKT/mTOR signaling pathway plays a key role in statin-induced myotoxicity.
 
Bonifacio A(1), Sanvee GM(1), Bouitbir J(2), Krähenbühl S(3).
 
Author information: 
(1)Division of Clinical Pharmacology & Toxicology, University Hospital, Basel,
Switzerland; Department of Biomedicine, University of Basel, Switzerland.
(2)Division of Clinical Pharmacology & Toxicology, University Hospital, Basel,
Switzerland; Department of Biomedicine, University of Basel, Switzerland; Swiss
Centre of Applied Human Toxicology (SCAHT), University of Basel, Switzerland.
(3)Division of Clinical Pharmacology & Toxicology, University Hospital, Basel,
Switzerland; Department of Biomedicine, University of Basel, Switzerland; Swiss
Centre of Applied Human Toxicology (SCAHT), University of Basel, Switzerland.
Electronic address: stephan.kraehenbuehl@usb.ch.
 
Statins are drugs that lower blood cholesterol levels and reduce cardiovascular
morbidity and mortality. They are generally well-tolerated, but myopathy is a
potentially severe adverse reaction of these compounds. The mechanisms by which
statins induce myotoxicity are not completely understood, but may be related to
inhibition of the AKT signaling pathway. The current studies were performed to
explore the down-stream effects of the statin-associated inhibition of AKT within
the AKT signaling pathway and on myocyte biology and morphology in C2C12 myotubes
and in mice in vivo. We exposed C2C12 myotubes to 10 μM or 50 μM simvastatin,
atorvastatin or rosuvastatin for 24 h. Simvastatin and atorvastatin inhibited AKT
phosphorylation and were cytotoxic starting at 10 μM, whereas similar effects
were observed for rosuvastatin at 50 μM. Inhibition of AKT phosphorylation was
associated with impaired phosphorylation of S6 kinase, ribosomal protein S6,
4E-binding protein 1 and FoxO3a, resulting in reduced protein synthesis,
accelerated myofibrillar degradation and atrophy of C2C12 myotubes. Furthermore, 
impaired AKT phosphorylation was associated with activation of caspases and PARP,
reflecting induction of apoptosis. Similar findings were detected in skeletal
muscle of mice treated orally with 5 mg/kg/day simvastatin for 3 weeks. In
conclusion, this study highlights the importance of the AKT/mTOR signaling
pathway in statin-induced myotoxicity and reveals potential drug targets for
treatment of patients with statin-associated myopathies.
 
Copyright © 2015 Elsevier B.V. All rights reserved.
 
PMID: 25913013

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Yet Another form of CR / CE Synergy Suggested by Speakman's Research

 

Here is my long-promised post about Speakman's body of research on metabolic rate and its relationship to cold exposure (CE), mitochondrial uncoupling, and longevity. In it, I'll point to studies by Speakman and his group that seem to suggest a new form of synergy between CR & CE, and a different, complementary reason for why neither works to extend health and longevity without the other. In it, I'll both bash and promote some of Michael's ideas, so I hope it will be provocative and entertaining to boot.

 

The study that seems to have kicked it off for Speakman was this one [1] from 2004 in which he and his group found in mouse housed at a chilly (for mice) 22°C:

 

... a positive association between metabolic intensity (kJ food assimilation / day expressed as g/body mass) and lifespan... Mice in the upper quartile of metabolic intensities had greater resting oxygen consumption by 17% and lived 36% longer than mice in the lowest intensity quartile. Mitochondria isolated from the skeletal muscle of mice in the upper quartile had higher proton conductance than mitochondria from mice from the lowest quartile. The higher conductance was caused by higher levels of endogenous activators of proton leak through the adenine nucleotide translocase (ANT) and uncoupling protein-3. Individuals with high metabolism were therefore more uncoupled, had greater resting and total daily energy expenditures and survived longest - supporting the 'uncoupling to survive' hypothesis.

 

[T]he association persisted whatever method we used to normalize the expression of energy metabolism for individual differences in body mass. There can be no doubt therefore over whether the association is an artefact of the manner in which metabolic rates were expressed. The magnitude of the effect was also impressive with a 36% difference in lifespans between the animals with the lowest 25% and highest 25% of metabolic rates. This is equivalent to an age difference in humans from 75 to 102 years.

 

The fact that the skeletal muscle mitochondria were more uncoupled via controlled proton channels (ANT and UCP-3) rather than simply leakier due to greater mitochondrial desaturation, deserves special mention and attention. To amplify this observation, another study by Speakman et al [2] found that mice with higher metabolic rate actually had less desaturated liver membranes, with significantly higher levels of the saturated fat palmitate (16:0). There was a strong positive correlation between metabolic rate and 16:0 content in liver.

 

There was no association between RMR or mass adjusted RMR and the proportional representation of any other fatty acid, including 22:6 (DHA) [and MUFA oleic acid (18:1)predicted by the membrane pacemaker hypothesis to be of particular significance.

 

This is paradoxical, because an elevated metabolic rate one might think would results at least in part from an increase in membrane desaturation (i.e. more PUFAs like DHA and less unsaturated fatty acids like MUFA and SFA in membranes), since desaturated membranes are (passively) leakier than more saturated membranes. Of course this was just liver membranes in general, and not necessarily reflective of liver mitochondrial membranes (MMs), or membranes (MMs or otherwise) in other tissues and organs. Nevertheless, Speakman et al were at a bit of a loss to explain this paradoxical finding, saying "the mechanism tying together increased membrane saturation with elevated RMR remains unclear."

 

In short, Speakman, his collaborators, and other researchers appear to have been somewhat baffled (at least in the first decade of this century) about what was causing the wide variability in fat-free-mass adjusted metabolic rate, and what might explain the observation (from [1]) that whatever the cause of this mysterious variation in metabolic rate, it seems to be associated with increased longevity, at least in mice. Study [2] shows that if anything, the long-lived mice with a higher metabolic rate have less leaky membranes, which should be associated with a lower metabolic rate, rather than a higher one.

 

But this "low membrane leakage → ↑ longevity" relationship is in accord with Michael's DHA-accelerated Aging Hypothesis, which postulates that one important way that CR works is to keep (mitochondrial) membranes more saturated, and therefore less leaky and peroxidation prone. But if MMs are less leaky, what accounts for the mysterious increase in metabolic rate in Speakman's long-lived mice, and the wider observation that CR does not decrease fat-free-mass-adjusted metabolic rate, despite the fact that if the MMs of CR rodents are less leaky this should reduce energy wasted in heat generation.

 

It seems that Speakman et al (2005) [3] might have part of the answer to this mystery of what was burning all the calories in metabolically hyperactive, long-lived mice - and the answer is BAT. Study [3] is interesting, because it is one of the few I've found that combine CR with measurements of BAT tissue. Speakman et al found, paradoxically again, that CRed rats housed at a relatively cool 24 °C had a higher than predicted mass-adjusted metabolic rate - expending 30-50% more calories than predicted based on a variety of models of how many calories they should be burning based on their body composition. They also found:

 

"In all these tissues, except brown adipose tissue, the wet masses were lower in the CR rats than their AD counterparts. The pattern for brown adipose tissue was exceptional in that the mass of this tissue was more than doubled in size in the CR animals at both ages."
 
To see just how comprehensive Speakman's assessment of tissue masses were in this study, and how dramatic an outlier the increase in BAT tissue in CR rats was relative to all the other tissues measured, check out this table from [3]. It shows the weight of all the different tissues Speakman et al tested in ad lib and CR mice at 6 and 26 months of age.
DTy9Pd4.png
 
For each tissue, the mean weight of the tissue for the group (AL or CR) with the larger tissue mass is highlighted in green and the lower group in in red. As you can see, for virtually every tissue at both ages, the tissue mass was larger in ad lib fed rats than CR rats. The one dramatic exception was BAT, which was over twice as large in CR rats than ad lib rats. Here was Speakman et al's commentary on this surprising result:
 
The greater than anticipated metabolism of the CR rats, combined with BAT hypertrophy, our previous observation of elevated UCP-1 protein levels and the significantly higher state four respiration in BAT mitochondria of CR rats (Lambert et al., 2004) strongly suggests that there is a shift in the thermoneutral zone in CR rats, such that the CR animals were under mild thermoregulatory stress at our housing temperature (24 °C).

 

So much for Michael's suggestion here that CR mice housed at an even lower temperature (20-22 °C) are only "very modestly cooler-housed than a human in normal room temperatures." No, even at 24 °C, CR rodents appear to be pumping up their BAT to cope with the thermal stress, at least according to Speakman's data and his hypothesis as expressed above. Ironically, this is the same JR Speakman who Michael tried to quote as supporting Michael's (unfounded) contention that rodents aren't really very thermally stressed at room temperature. As I pointed out in my Albatross cold exposure post, Speakman himself contradicts Michael's contention, saying instead:

 

At no point in our paper do we state that mice are ‘most comfortable’ at 20–22 °C, and the contention of our article was not, and was never stated to be, that ‘there is no distressing impact of cold temperatures on mice’
 

Here we see perhaps a big reason why Speakman doesn't deny thermal stress in rodents at room temperature - one of his own studies [3] shows quite dramatically that CR rats housed at slightly above normal room temperature are sacrificing all their other tissues due to lack of calories (i.e. burning the furniture when their supply of firewood is cut off), but building up BAT at the same time in order to keep from freezing their skinny little butts off.

 

And if BAT has no conceivable part to play in aging per se, as Michael suggests here, why the heck is BAT the only tissue except the brain that is spared by CR, and the only tissue that CR increases in mass relative to ad lib?

 

So let's step back and consider what these three Speakman studies seem to be telling us.

 

From [1] we see that mice with a naturally high metabolic, as measured by either oxygen consumption or food consumption per gram of body weight, lived longer than mice with a slower metabolic rate. From [2] we see the membranes of the metabolically hyperactive mice didn't appear to be passively leakier due to membrane desaturation; quite the opposite in fact - at least some of their membranes (e.g. liver) were less desaturated rather than more. Instead, part of the explanation for increased metabolic rate appeared to be as a result of controlled (rather than passive) leakage across the mitochondrial membrane (MM) in skeletal muscles. 

 

From [3], we see that, like the metabolically hyperactive, long-lived mice in [1], CR rats have a 30-50% higher than predicted metabolic rate when housed at cool temperatures. They also had a lot more BAT. Speakman suggests that the CR rats in [3] had a boosted metabolism as a result of BAT-thermogenesis. Also like the metabolically hyperactive, long-lived mice in [1], we know that CR rodents appear to have less desaturated MMs. In fact the idea of keeping MMs desaturated is the whole idea behind Michael's DHA-accelerated Aging Hypothesis. And of course, CR rodents live longer, at least if housed at cool temperatures.

 

So what is all this telling us? Let me try to pull it together into a theory. Note the following is just a theory, based on the evidence from Speakman and elsewhere.

 

If Michael is right, to extend lifespan we want to keep our membranes (especially MMs) saturated to avoid peroxidation and free radical damage to our mitochondria and their DNA. But more saturated MMs are less (passively) leaky - they are more tightly packed without all those double bonds, so it's harder for protons to slip through the gaps in the mitochondrial membrane. But with less proton leakage, there will be a higher proton gradient across the MM, and this will in turn increase the likelihood of "electron fumbling" in the electron transport chain the mitochondria employ to produce ATP. Fumbled electrons lead to an increase in ROS generation and therefore an increase in the very kind of membrane damage that we were trying to avoid by keeping our MMs saturated in the first place! And less leaky membranes mean less heat production, since passive leakage of protons across a leaky mitochondrial membrane is one important way mitochondria generate heat to keep the animal warm. 

 

So that's not good - if animals keep their MMs highly saturated to avoid age-inducing MM peroxidation, they'll increase free radical production that will damage the mitochondria anyway. And to add insult to injury, they may not be able to generate enough heat to keep from freezing at normal room temperature, which is chilly for rodents.

 

[Here is the scene in the movie where cold exposure rides in on a white horse to the rescue .]

 

Here is where (by my hypothesis) the synergy between CR and CE comes in. In brief, cold exposure does several things to mitigate the CR-induced problems associated with keeping MMs highly saturated. First CE increases BAT, and quite possible sarcolipin-mediated futile cycling in the sarcoplasmic reticulum of muscle fibers as discussed here. These two effects of CE enable the animals to stay warm enough to survive while keeping MMs nice and saturated, and therefore less prone to damage - no passive MM proton leakage required to keep warm. Second, by increasing the expression of uncoupling proteins to actively let protons cross the MM, CE enables mitochondria to generate heat to keep the animal warm, and at the same time reduces the proton gradient across the MM, and hence reduces free radical production that would otherwise damage the mitochondria.

 

Put another way, what I'm suggesting (hypothesizing) is that CR keeps MMs "tight" and damage-resistant. But then CE comes along and makes changes so that the "tight" mitochondria let protons slip through via a different, more-controlled channel (i.e. UCPs) so as to prevent the overly leak-proof membranes (and resulting high proton gradient) from generating damaging free radicals. At the same time CE helps out by reducing the thermogenic requirements normally placed on mitochondria by supplementing it with increased BAT- and sarcolipin-induced thermogenesis. So this allows CR to keep MMs "tight" (highly saturated) in most body tissues (but especially important, in skeletal muscle tissue), while still allowing the animal to cope with the cold. 

 

Suggestive (albeit indirect) support for this theory comes from the study that Michael points to as the best direct evidence for his DHA-accelerated Aging Hypothesis, namely PMID 25313149. That study found that CR mice fed high-SFA lard as their primary fat source had less peroxidation-prone mitochondrial membranes and lived longer than CR mice fed high-PUFA soybean oil or high-HUFA fish oil. From the full text, the mice in Michael's lard study were all housed at normal lab temperatures (22-24 °C), which is chilly for mice. So, like almost all rodent CR studies, Michael's was a test of the combination of CR and CE. 

 

A good test of my hypothesis that it takes CE on top of CR to get the full benefit of the CR-induced increase in mitochondrial membrane saturation would be to repeat this study at a thermoneutral housing temperature to see if lard-feeding still increased the lifespan of CR mice. If I'm right, than the lard-fed CR mice wouldn't enjoy a lifespan advantage, since the effects of CE wouldn't kick in to reduced the proton gradient across the highly leak-resistant mitochondrial membranes of lard-fed CR mice, resulting in increased free radical damage to mitochondria (and no lifespan extension) despite their highly saturated mitochondrial membranes.

 

In short, I postulate that without cold exposure, CR will still keep MMs highly saturated. But without CE to facilitate active (channel-mediated) proton flow across the MM, the proton gradient will be too high, resulting in free radical creation and mitochondrial damage. And this may be part of the reason why CR at thermoneutrality doesn't extend lifespan.

 

Conversely, without calorie restriction (i.e. without a net calorie deficit), MMs will be more desaturated. As a result, more damage will be done to these vulnerable, desaturated MMs by free radicals generated by the mitochondria - thereby accelerating aging. And cold exposure won't come to the rescue without CR since the (passively) leakier unsaturated MMs will generate enough heat to keep the animals warm. Plus, without a net calorie deficit, the animals will have enough thermal insulation not to need to generate much heat in the first place. So CE won't need to upregulate UCPs in mitochondrial, or increase BAT synthesis, or increase (relatively harmless) sarcolipin-induced thermogenesis. Leaky, desaturated and damage-prone mitochondria will be sufficient to generate all the heat required to keep chubby, AL-fed, cold-exposed rodents warm. This would explain why CE without CR doesn't extend lifespan.

 

In summary, together these three Speakman papers seem to suggest a new form of synergy between CR & CE. In this post I tried to show that such synergies makes sense from an evolutionary perspective. In this post I pointed to a different, organ-level synergy between the two - namely, by activating mTOR through a "backdoor" pathway (PKA), CE promotes certain important anabolic processes (like the synthesis of bone and immune system cells) which are normally clobbered by CR's suppression of the insulin/IGF-1 signalling pathway.

 

Here we see what may be a different CR + CE synergy, which may be of more fundamental importance for slowing the aging process. In short, according to Michael an important anti-aging effect of CR is to keep (mitochondrial) membranes damage-resistant by keeping them "tight" (highly saturated). But due to the resulting higher proton gradient, these tight membranes would normally promote the creation of age-inducing free radicals. CE prevents this potentially deleterious effect of CR by a) promoting thermogenesis elsewhere (in BAT and muscle sarcoplasmic reticulum) so mitochondria don't need to generate as much heat through passive leakage, and b) by promoting active proton transport across the mitochondrial membrane to generate heat while remaining highly saturated, and as a fortuitous side-effect reducing the proton gradient near the mitochondrial membranes so as to reduce age-inducing free radical production.

 

Michael - you've been very quiet on this thread lately, despite some meaty posts I was hoping to get your feedback on. Perhaps this one will rise to the level of your attention since it bears directly on your DHA-accelerated Aging Hypothesis...

 

Finally, it's cool that Speakman will be at the upcoming CR conference, so we can probe him on what he thinks about all this. Michael, does Speakman have a topic for his talk already picked out? 

 

--Dean

 

--------

[1] Aging Cell. 2004 Jun;3(3):87-95.

 
Uncoupled and surviving: individual mice with high metabolism have greater
mitochondrial uncoupling and live longer.
 
Speakman JR(1), Talbot DA, Selman C, Snart S, McLaren JS, Redman P, Krol E,
Jackson DM, Johnson MS, Brand MD.
 
 
Two theories of how energy metabolism should be associated with longevity, both
mediated via free-radical production, make completely contrary predictions. The
'rate of living-free-radical theory' (Pearl, 1928; Harman, 1956; Sohal, 2002)
suggests a negative association, the 'uncoupling to survive' hypothesis (Brand,
2000) suggests the correlation should be positive. Existing empirical data on
this issue is contradictory and extremely confused (Rubner, 1908; Yan & Sohal,
2000; Ragland & Sohal, 1975; Daan et al., 1996; Wolf & Schmid-Hempel, 1989]. We
sought associations between longevity and individual variations in energy
metabolism in a cohort of outbred mice. We found a positive association between
metabolic intensity (kJ daily food assimilation expressed as g/body mass) and
lifespan, but no relationships of lifespan to body mass, fat mass or lean body
mass. Mice in the upper quartile of metabolic intensities had greater resting
oxygen consumption by 17% and lived 36% longer than mice in the lowest intensity 
quartile. Mitochondria isolated from the skeletal muscle of mice in the upper
quartile had higher proton conductance than mitochondria from mice from the
lowest quartile. The higher conductance was caused by higher levels of endogenous
activators of proton leak through the adenine nucleotide translocase and
uncoupling protein-3. Individuals with high metabolism were therefore more
uncoupled, had greater resting and total daily energy expenditures and survived
longest - supporting the 'uncoupling to survive' hypothesis.
 
Copyright 2004 Blackwell Publishing Ltd.
 
PMID: 15153176
 
---------
[2] Mech Ageing Dev. 2008 Mar;129(3):129-37. Epub 2007 Nov 17.
 
Intra-specific variation in resting metabolic rate in MF1 mice is not associated 
with membrane lipid desaturation in the liver.
 
Haggerty C(1), Hoggard N, Brown DS, Clapham JC, Speakman JR.
 
Author information: 
(1)Aberdeen Centre for Energy Regulation and Obesity (ACERO), School of
Biological Sciences, University of Aberdeen, Aberdeen, Scotland AB21 9SB, UK.
 
The 'membrane pacemaker' hypothesis provides a putative mechanistic linkage
between variations in energy metabolism, rates of ageing and lifespan across
different species. Within species we have found positive associations between
longevity and metabolism, which contrast the inter-specific trends. It is of
interest to know therefore how levels of lipid desaturation in membranes are
linked to variation in metabolism between individuals within species. We explored
this problem by extracting membrane fatty acids from the livers of mice that
varied in their metabolic rate, in a strain (MF1) where we have previously
demonstrated a positive association between metabolism and lifespan. We measured 
resting metabolic rate (RMR) in 60 mice, each measured on three occasions, and
measured their body compositions using dual energy X-ray absorptiometry (DXA). We
selected 28 individuals that exhibited a wide variation in their mean resting
metabolic rates (RMR) and extracted membrane lipids from the livers of these mice
post mortem and analysed them for the patterns of contribution of different fatty
acids. We then sought associations between the levels of membrane desaturation
and the individual variability in RMR, using the proportional contributions of
each fatty acid as predictors in a stepwise regression or by re-describing the
variation in fatty acyl lipids using a PCA analysis and then seeking associations
between scores on the derived components and RMR. We used whole animal RMRs and
also RMR with the effects of body composition (fat free mass) removed. The level 
of individual variation in RMR was consistent with our previous observations.
There was a significant positive association (p=0.019) between the proportion of 
palmitic acid (16:0) in the membranes and RMR, which was strengthened (p=0.014)
when we adjusted RMR for differences in fat free mass. The proportion of palmitic
acid (16:0) explained 20.9% of the individual variation in residual RMR. There
was no association between RMR or mass adjusted RMR and the proportional
representation of any other fatty acid, including 22:6 (DHA) predicted by the
membrane pacemaker hypothesis to be of particular significance. High levels of
saturated fatty acids in the membranes of mice with high rates of metabolism may 
contribute to their greater longevity, but the mechanism tying together increased
membrane saturation with elevated RMR remains unclear.
 
PMID: 18160096
 
----------
[3]  Mech Ageing Dev. 2005 Jun-Jul;126(6-7):783-93. Epub 2005 Mar 16.
 
Energy expenditure of calorically restricted rats is higher than predicted from
their altered body composition.
 
Selman C(1), Phillips T, Staib JL, Duncan JS, Leeuwenburgh C, Speakman JR.
 
Author information: 
(1)University of Florida, Department of Aging and Geriatric Research, College of 
Medicine, Gainesville, 32608, USA. c.selman@ucl.ac.uk
 
Debate exists over the impact of caloric restriction (CR) on the level of energy 
expenditure. At the whole animal level, CR decreases metabolic rates but in
parallel body mass also declines. The question arises whether the reduction in
metabolism is greater, smaller or not different from the expectation based on
body mass change alone. Answers to this question depend on how metabolic rate is 
normalized and it has recently been suggested that this issue can only be
resolved through detailed morphological investigation. Added to this issue is the
problem of how appropriate the resting energy expenditure is to characterize
metabolic events relating to aging phenomena. We measured the daily energy
demands of young and old rats under ad libitum (AD) food intake or 40% CR, using 
the doubly labeled water (DLW) method and made detailed morphological examination
of individuals, including 21 different body components. Whole body energy demands
of CR rats were lower than AD rats, but the extent of this difference was much
less than expected from the degree of caloric restriction, consistent with other 
studies using the DLW method on CR animals. Using multiple regression and
multivariate data reduction methods we built two empirical predictive models of
the association between daily energy demands and body composition using the ad
lib animals. We then predicted the expected energy expenditures of the CR animals
based on their altered morphology and compared these predictions to the observed 
daily energy demands. Independent of how we constructed the prediction, young and
old rats under CR expended 30 and 50% more energy, respectively, than the
prediction from their altered body composition. This effect is consistent with
recent intra-specific observations of positive associations between energy
metabolism and lifespan and theoretical ideas about mechanisms underpinning the
relationship between oxygen consumption and reactive oxygen species production in
mitochondria.
 
PMID: 15888333

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I've been doing more rigorous personal experiments on cold exposure and its affect on my blood glucose (a well documented relationship covered in several studies posted in this thread).  Just for some background, I've been rather closely tracking my blood glucose for about 18 months now.  I became interested in this because higher circulating glucose is linked to aging, glycation, and damage to numerous human organs over time.  During that timeframe I've done well over a 100 readings.  Even after going weeks on 100% low GI foods, AND fasting, the lowest reading I ever saw was 67 mm/dL and I put a GREAT deal of effort into even achieving that level.  I use a TRUEResult test meter which has among the best reviews on Amazon (and cheapest test strips!) in case anyone is interested.  I have taken readings with this meter before and after being lab tested, and it was spot on accurate with the lab results, several healthcare companies actually require their diabetic customers to use this meter.  I'm giving you this background because I have been very surprised by the results I am now achieving with CE.  I've only been intentionally doing CE for 5 or 6 weeks, during that time I went from a typical always cold, CR "wimp" to someone who can lay around all day in a cold house wearing nothing but boxers and actually feel hot thanks to thermogenesis (and not only feel an actual burning sensation, but often even sweat without exercising).

 

Below is my log from today... (Note that I never wore a cooling vest AT ALL today)

 

Glucose reading shortly after waking up = 77mg/dL (7:26AM)

1.jpg

Drive kids to school, by now they have learned to bundle up in winter coats despite the fact that Dad is wearing only a t-shirt and shorts, cuz there won't be any heat ;).  41F degree air blowing on me the whole time (I can handle 20's!).  I take my shirt off after dropping off the kids (still seems too socially unacceptable / creepy to go shirtless with the kids in the car), another 30 minutes of 41F degree air (1 hour total) and I'm back at home for a work from home day.  Despite no heating, the house is 65F degrees and will remain exactly that temperature for the rest of the day (I'd prefer it a bit cooler but this will do).  5 hours go by working from home in 65 degrees wearing only boxers and socks (at least one study I read used 66F degree air with beneficial results).  That's 6 hours total of mild CE.

I generally only eat between 12PM and 7PM.

I have found that CE+fasting past a normal eating time results in surprisingly low blood glucose levels (Dean previously posted in this thread a study showing a glucose lowering effect from thermogenesis in anticipation of eating, almost like salivating).   Importantly, these low levels HAVE NOT resulted in hypoglycemic symptoms (I felt great all day today, thinking clearly, getting work done, etc).

Fasting slightly past normal meal time, I take a reading: 63mg/dL (12:31PM)

2.jpg

Mild (65F) CE continues through entire day.  I prepare what I would consider a typical, CRON, large meal:

meal.jpg

For some reason I missed one item above, for the sake of completeness and because red chili peppers have been shown to synergistically (with CE) boost thermogenesis, here it is:

pepper.jpg

Meal Stats:

mealinfo.png

1410 calories of pure goodness!  I finish eating all of the above, at 1:45PM.

10 minutes post prandial = 75mg/dL (1:55PM)

3.jpg

30 minutes post prandial = 67mg/dL (2:16PM)

4.jpg

I wanted to test the idea that maybe a "cold finger" or "bad circulation" could cause lower readings - so at this point I did a high intensity cardio workout (running up and down stairs wearing a 40 lbs. weight vest for a few minutes), then I ran my hand under hot water to warm it up.  I thoroughly dried hands/fingers and took another reading.

40 minutes post prandial, post exercise, post hand warming = 59mg/dL!  (2:25PM)

5.jpg

The low readings don't seem to have anything to do with circulation or cold fingers.

I want to note again, I was feeling good this whole time, no hypoglycemic symptoms whatsoever.

There seems to be potential for even mild CE to do good things for health and longevity.  

I feel like there is some connection between meal content (carbs/sugar vs. fat) and/or exercise that contributes to maximal thermogenesis.  Even an hour after my little "stair run", just sitting in a cool room -- my neck, collarbone area, ribs, and thighs feel like they are burning up, definitely "feels" like peak thermogenesis for the day right now (3-4PM).

By 5:22PM I'm back up to 68:

6.jpg

 

 

 

Areas for further research:

  • Best way to "ignite" thermogenesis (Best temps? How long? Continuous or intermittent? How does food affect it and what foods are best? How does exercise affect and what type/duration?) 
  • Are these readings in the 50's accurate?  The next time I get lab tested I will try to go when my meter has a reading in the 50's to confirm.  Many people would experience hypoglycemic symptoms at these levels but that is not the case for me, is there something interesting going on to account for that with regards to the CE processes?

 

Also I want to reiterate one thing - some people that do CR seem to think they are getting CE because they feel cold all the time or have a low measured body temperature.  Feeling cold is not evidence that you are "doing CE", in fact it probably indicates that you aren't.  Until you feel the burn of wonderful thermogenesis while sitting naked in a cold room, you haven't experienced CE!   :Dxyz

 

To be continued... next I will post my log from a crazy high GI meal with nearly double the sugar of today's meal.  What will happen??  Stay tuned to find out!  Post your own log, I want to compare results with others.  

 

Regards,

Gordo

Edited by Gordo

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Gordo,

 

Those are some amazing glucose results - Congratulations!

 

I presume you wouldn't be posting with such enthusiasm to this thread if such good glucose control has always been the norm for you. What was your typical fasting and postprandial glucose like before you started your intentional cold exposure experiments?

 

I wholeheartedly agree that simply feeling cold (as most CRers do) and having a low body temperature (as most CRers do) is very unlike the subjective experience one gets in response to cold after chronic cold exposure. There is definitely a feeling of warmth emanating from parts of the body, especially the upper torso, that kicks in in response to cold after you've been doing it for a while.

 

The mere fact that you and I seem almost impervious to cold these days is also evidence of the substantial metabolic changes our bodies have undergone.

 

Have you noticed any changes in your weight, and have you changed your diet (content or quantity) as a result of CE?

 

Thanks again for so thoroughly documenting your glucose readings from yesterday. It's quite inspirational!

 

--Dean

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I presume you wouldn't be posting with such enthusiasm to this thread if such good glucose control has always been the norm for you. What was your typical fasting and postprandial glucose like before you started your intentional cold exposure experiments?

 

 

I am excited to have such phenomenal glucose control WITHOUT having to severely restrict dietary choices to achieve it.  The CE Way (I should trademark that) is so much more effective than anything I have tried previously!  I alluded to this earlier, but before CE my lowest reading ever was 67 and that was a fasting value, there is no chance at all I'd see that number soon after a meal, and that was also after being careful about only eating low GI foods.  Having a post prandial peak of 75 after a 1400 calorie meal is totally unprecedented for me (and that meal had lots of high GI foods like rice, banana and other sweet fruit).  Its hard to say what my post prandial peak would have been for this meal without CE, I'm guessing maybe 115-120?  I did intend to do control readings, and I probably still will eventually, but right now I don't feel like stopping CE just to get a control reading, perhaps I'll do it when Summer comes and my house is hot (I'm not sure how quickly/completely the CE related enhanced glucose control goes away when you stop CE?)

 

 

Have you noticed any changes in your weight, and have you changed your diet (content or quantity) as a result of CE?

 

I've been keeping my weight relatively constant by adjusting my caloric intake as needed.  I have not been recording my food intake so I don't really know how much my daily caloric intake has changed, if I had to guess, I would say from 100-400 extra daily calories depending on how much and how intense the CE was that day.  As far as content, I'm much more relaxed now about eating high GI foods, for example before CE I would never eat bananas, and even though I grow my own awesome organic apples, I was mostly just eating the skins and not fully enjoying the wonderful sweet flesh.  I have no problem now with eating any type of fruit in almost any quantity within reason.  I have also been eating more honey and maple syrup which have interesting reported health benefits but were previously "off limits" from my perspective.

Edited by Gordo

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Dean,

 

'Not sure if your CR + CE analysis is correct (I think it is) but consider it brilliant, and pioneering to CR thinking.  

 

Even if a human may not have substantial BAT, sarcolipin induced thermogenesis (relatively harmless) would appear likely to do a lot of good from various meaningful angles as referenced/indicated in the above 9 pages.

 

Thank you for the effort and the unmatched aptitude.

Edited by Kenton

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All,

 

Chalk up another one for the benefits of cold exposure and the resulting increased thermogenesis.

 

Recall from this post that genetically elevated Fibroblast Growth Factor 21 (FGF21) levels resulted in a 40% increase in mouse lifespan, with a slight increase in food intake (PMID 23066506). Along with living longer, the mice with elevated FGF21 exhibited lower insulin, lower IGF-1, and better glucose control than the wild-type mice. And furthermore, CR on it's own does not elevate FGF21.

 

And recall in this post we saw that FGF21 was instrumental at maintaining a healthy thymus and immune system - low levels of FGF21 resulted in thymus atrophy and high levels resulted in a healthier-than-normal thymus in aging mice. The thymus is responsible for generating immune system T-cells, which we know are critical for immune function and cancer prevention. So it is no surprise that higher expression of FGF21 resulted in greater T-cell synthesis. As one of the authors of PMID 26755598 put it: "FGF21 protects the immune system against the ravages of age".

 

With that background/refresher in mind - this recent study [1] in humans, which I somehow previously overlooked, found a few interesting things:

  1. FGF21 was increased by acute cold exposure in proportion to how much BAT activity people exhibited in response to cold. In other words, people with a lot of BAT showed higher levels of FGF21 in response to cold.
  2. "High levels of FGF21 were associated with an increase in core temperature, while low levels of FGF21 are associated with a decrease in core temperature upon cold exposure." In other words, subjects only exhibit a high level of FGF21 if they were cold-acclimated and therefore prepared to defend core body temperature (via BAT thermogenesis or other means) in response to cold. 
  3. Ten days of cold acclimation resulted in both an increase in people's BAT activity in response to cold and a 30% increase in basal circulating FGF21. 

Here are two of the most interesting graphs from the paper:

 

rA06SIl.png

 

The graph on the left shows just how correlated BAT activity and cold-exposed FGF21 levels were: high BAT activity → high FGF21 concentration. In other words, both BAT activity and FGF21 were boosted by cold exposure, in a highly correlated fashion, although it's unclear which way the arrow of causality between BAT activity & FGF21 level points. 

 

The graph on the right drives home point #2 in a dramatic fashion, and is especially noteworthy for CR folks. Getting cold (i.e. a drop in body temperature) in response to being in the cold was negatively correlated with FGF21 level. Instead, being cold-acclimated and therefore ready to not just maintain, but increase core body temperature in response to cold exposure was critical if one was to exhibit high FGF21 - and not just high FGF21 in response to cold, but high FGF21 all the time.

 

In short, if you want to enjoy the immune-boosting, Insulin/IGF-1 lowering, cancer-preventing, and potentially life-extending benefits of elevated FGF21, it looks like it's critical to be cold-acclimated, and not simply feel or be chilly in response to a cold environment. In fact being chilly in the cold, as many cold-eschewing CR folks report, appears to be counterproductive/contraindicated if one hopes to have a high level of beneficial FGF21.

 

These results seem to pretty strongly support my theory that CR and CE act synergistically, and that CR without CE could very well be ineffective and ill-advised, in part because CR without CE undermines immune system competence.

 

--Dean

 

------------

[1] Sci Rep. 2015 May 18;5:10275. doi: 10.1038/srep10275.

Serum FGF21 levels are associated with brown adipose tissue activity in humans.

Hanssen MJ(1), Broeders E(2), Samms RJ(3), Vosselman MJ(1), van der Lans AA(1),
Cheng CC(3), Adams AC(3), van Marken Lichtenbelt WD(1), Schrauwen P(1).

Author information:
(1)Department of Human Biology, NUTRIM School for Nutrition and Translational
Research in Metabolism,Maastricht University Medical Centre+(MUMC+), Maastricht,
the Netherlands. (2)1] Department of Human Biology, NUTRIM School for Nutrition
and Translational Research in Metabolism,Maastricht University Medical
Centre+(MUMC+), Maastricht, the Netherlands [2] Department of surgery, Maastricht
University Medical Centre+(MUMC+), Maastricht, the Netherlands. (3)Lilly Research
Laboratories, Lilly Corporate Center, Indianapolis, IN, USA 46285.

The obesity pandemic has spurred a need for novel therapies to prevent and treat
metabolic complications. The recent rediscovery of brown adipose tissue (BAT) in
humans made this tissue a possible therapeutic target, due to its potentially
substantial contributions to energy homeostasis. Fibroblast growth factor 21
(FGF21) has been identified as a facilitator of cold-induced thermogenesis in
humans. Furthermore, pre-clinical studies revealed that FGF21 administration
leads to improvement in the metabolic consequences of obesity, such as
dyslipidemia and type 2 diabetes. Here we studied plasma FGF21 levels in two
cohorts of human subjects, in whom BAT activity was determined using an
individualized cooling protocol by [(18)F]FDG-PET/CT scan. Importantly, we found
that circulating FGF21 levels correlated with BAT activity during acute cold
exposure in male subjects. In addition, FGF21 levels were related to the change
in core temperature upon acute cold exposure, indicating a role for FGF21 in
maintaining normothermia, possibly via activation of BAT. Furthermore, cold
acclimation increased BAT activity in parallel with increased FGF21 levels. In
conclusion, our results demonstrate that FGF21 levels in humans are related to
BAT activity, suggesting that FGF21 may represent a novel mechanism via which BAT
activity in humans may be enhanced.

PMCID: PMC4434994
PMID: 25985218

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