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Bone Health May Recover with Time on CR

Dean Pomerleau

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Here is another gem of a study [1] from James Cain latest weekly CR research update (thanks James!) worth its own thread.


In this study, the researchers subjected mice to pretty severe (40%) CR either starting very young (4 weeks) or starting late in life (48 or 68 weeks).


CR started in the oldest mice (68 weeks) and lasting for 12 weeks had negative effects on their bone health.


When CR was started young (4 weeks), there was an initial period when the bone health of the CR'ed mice was profoundly compromised, both in terms of bone mineral density and force required to break the femur. 


But over the lifetime of the early-onset CR'ed mice, their bone health improved markedly, both in terms bone mineral density and the microarchitecture of the bone.


In short, the bones of mice who started CR at a young age were light but strong when they got old.


That is comforting, and accords with the finding [2] from Luigi Fontana on some of us human calorie restrictors that our bones are healthy despite long-term CR.





[1] J Bone Miner Res. 2015 Nov 17. doi: 10.1002/jbmr.2745. [Epub ahead of print]

Dietary Restriction-Induced Alterations in Bone Phenotype: Effects of Lifelong
Versus Short-Term Caloric Restriction on Femoral and Vertebral Bone in C57BL/6

Behrendt AK(1,)(2), Kuhla A(2), Osterberg A(3), Polley C(2), Herlyn P(1), Fischer
DC(4), Scotland M(1), Wree A(5), Histing T(6), Menger MD(7), Müller-Hilke B(3),
Mittlmeier T(1), Vollmar B(2).

Caloric restriction (CR) is a well-described dietary intervention that delays the
onset of aging-associated biochemical and physiological changes thereby extending
the lifespan of rodents. The influence of CR on metabolism, strength and
morphology of bone has been controversially discussed in literature. Thus, the
present study evaluated whether lifelong CR versus short-term late-onset dietary
intervention differentially affects the development of senile osteoporosis in
C57BL/6 mice. Two different dietary regimens with 40% food restriction were
performed: lifelong CR starting in 4wk-old mice was maintained for 4, 20 or 74
weeks. In contrast, short-term late-onset CR lasting a period of 12 weeks was
commenced at 48 or 68 weeks of age. Control mice were fed ad libitum (AL). Bone
specimens were assessed using microcomputed tomography (µCT, femur and lumbar
vertebral body) and biomechanical testing (femur). Adverse effects of CR,
including reduced cortical bone mineral density (Ct.BMD) and thickness (Ct.Th)
were detected to some extent in senile mice (68 + 12w) but in particular in
cortical bone of young growing mice (4 + 4w), associated with reduced femoral
failure force (F). However, we observed a profound capacity of bone to compensate
these deleterious changes of minor nutrition with increasing age presumably via
reorganization of trabecular bone. Especially in lumbar vertebrae, lifelong CR
lasting 20 or 74 weeks had beneficial effects on trabecular bone mineral density
(Tb.BMD), bone volume fraction (BV/TV) and trabecular number (Tb.N). In parallel,
lifelong CR groups showed reduced structure model index values compared to
age-matched controls indicating a transformation of vertebral trabecular bone
microarchitecture towards a plate-like geometry. This effect was not visible in
senile mice after short-term 12-week CR. In summary, CR has differential effects
on cortical and trabecular bone dependent on bone localization and starting age.
Our study underlines that bone compartments possess a lifelong capability to cope
with changing nutritional influences. This article is protected by copyright. All
rights reserved.

This article is protected by copyright. All rights reserved.

PMID: 26572927



[3] Aging Cell. 2011 Feb;10(1):96-102. doi: 10.1111/j.1474-9726.2010.00643.x. Epub
2010 Nov 15.
Reduced bone mineral density is not associated with significantly reduced bone
quality in men and women practicing long-term calorie restriction with adequate
Villareal DT(1), Kotyk JJ, Armamento-Villareal RC, Kenguva V, Seaman P, Shahar A,
Wald MJ, Kleerekoper M, Fontana L.
Author information:
(1)Division of Geriatrics and Nutritional Science, Washington University School
of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
Calorie restriction (CR) reduces bone quantity but not bone quality in rodents.
Nothing is known regarding the long-term effects of CR with adequate intake of
vitamin and minerals on bone quantity and quality in middle-aged lean
individuals. In this study, we evaluated body composition, bone mineral density
(BMD), and serum markers of bone turnover and inflammation in 32 volunteers who
had been eating a CR diet (approximately 35% less calories than controls) for an
average of 6.8 ± 5.2 years (mean age 52.7 ± 10.3 years) and 32 age- and
sex-matched sedentary controls eating Western diets (WD). In a subgroup of 10 CR
and 10 WD volunteers, we also measured trabecular bone (TB) microarchitecture of
the distal radius using high-resolution magnetic resonance imaging. We found that
the CR volunteers had significantly lower body mass index than the WD volunteers
(18.9 ± 1.2 vs. 26.5 ± 2.2 kg m(-2) ; P = 0.0001). BMD of the lumbar spine (0.870
± 0.11 vs. 1.138 ± 0.12 g cm(-2) , P = 0.0001) and hip (0.806 ± 0.12 vs. 1.047 ±
0.12 g cm(-2) , P = 0.0001) was also lower in the CR than in the WD group. Serum
C-terminal telopeptide and bone-specific alkaline phosphatase concentration were
similar between groups, while serum C-reactive protein (0.19 ± 0.26 vs. 1.46 ±
1.56 mg L(-1) , P = 0.0001) was lower in the CR group. Trabecular bone
microarchitecture parameters such as the erosion index (0.916 ± 0.087 vs. 0.877 ±
0.088; P = 0.739) and surface-to-curve ratio (10.3 ± 1.4 vs. 12.1 ± 2.1, P =
0.440) were not significantly different between groups. These findings suggest
that markedly reduced BMD is not associated with significantly reduced bone
quality in middle-aged men and women practicing long-term calorie restriction
with adequate nutrition.
PMCID: PMC3607368
PMID: 20969721
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Unfortunately, the abstract of this study suffers the common flaw of misuse of qualitative descriptors of age and duration of onset of CR ("lifelong" and "late-onset"). A 4 wk-old mouse is barely weaned, and most CR studies don't begin until at least 6 weeks and often 8; a mouse at 48 weeks is not even a year old, and at 68 weeks is only 476 days old — about half of the ≈900 d average lifespan of a mouse from a reasonably healthy strain raised under good conditions, and only ≈44% of maximum — ie, by one way of calculating, equivalent to a human adult in hir early 40s. (It's not quite that simple because the rate of maturation of the species doesn't track linearly to extrapolate to lifespan, but as you can see on an attempt to map this out:




Representative age ranges for mature life history stages in C57BL/6J mice; comparison to human beings. (Adapted from Figure 20-3: Flurkey K, Currer JM, Harrison DE. 2007. The Mouse in Aging Research. In The Mouse in Biomedical Research 2nd Edition. Fox JG, et al, editors. American College Laboratory Animal Medicine (Elsevier), Burlington, MA. pp. 637–672.) Swiped from Life span as a biomarker, a page from David Harrison's lab at The Jackson Laboratories.



... it's still squarely in middle age for a mouse, granted that 476 d is a bit under 16 months.



I fear that all that's really going on with the weanlings is that they've been allowed to undergo normal childhood and (for a mouse) early adulthood skeletal growth, which while slowed continues on CR; what you're seeing in the "old" mice is the effect of CR on the bones of an organism that has completed its growth.

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Regarding bone health.  This is more important to people on CR than it is to the rest of the population.  If you have a BMI of 35 and smoke you will never get to be old enough to have serious repercussions result from a fracture; you will have plenty of padding to protect you in the case of a fall; and your bones will be more massive just from the effort of having to keep you upright.  We, however, have the opposite problems: no padding to speak of, smaller bones and a lifespan long enough that the consequences of fracture can be very serious indeed.  So I am wondering if a survey of members might be helpful on this. 


There would be two purposes of the survey:  A) So we each can compare our bone strength markers with those of others in the group to determine if we are doing a good, excellent or poor job in that department, and B) to take a look at those with the best DXA scores and try to figure out what it is they are doing to achieve such good results.


But for this we would need to be able to survey enough people willing to share their DXA scores anonymously with the person in charge of the survey.  I recently had a bone DXA test done but I have no idea how many others with DXA data there are in the group.


So the purpose of this note is to ask how many of us have had DXA tests done and would be prepared to share their data anonymously, so we might be able to learn how to better take care to avoid fracture when we get really old (even older than me, even!)


Please respond (either directly here or by any other method) if you would be happy to participate anonymously in such a survey.  Thank you.



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I've had a DXA and would be happy to participate. Further, I think it is a great idea, if we can get enough CR practitioners to participate.


But as has been discussed before, DXA scans, and bone mineral density in general, aren't a very good measure of fracture risk even for the general population, but particularly for thin people, due to calibration issues with the DXA machine having to do with assumed fat/lean mass ratios etc., and because our bones are lighter but not necessarily more prone to fractures, as the Fontana study I point to above (PMID: 20969721) suggests.


What would be better is if we had fracture data for a large number of CR practitioners, which we could compare with an age-matched group of the general population. I don't see that is likely however, given how small a cohort we are, and how rare fractures are, especially among those less than 70.


But I'm all for any kind of citizen science effort, so if we can share DXA results and correlate them with diet and lifestyle factors, that would be great!



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Yes.  It seems very unlikely we would have enough cases of fracture to learn anything from that!  I certainly hope so!  But if some people have far better, or far worse, DXA z-scores etc then we might be able to learn something important from that. 


You can be 70 and have a biological age of 50 and trip on the sidewalk and possibly die from the fracture consequences, so bone issues seem to me to be unusually important for us.  Not so much for someone aged 70 who is going to drop dead from CVD tomorrow anyway.



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Unfortunately, the abstract of this study suffers the common flaw of misuse of qualitative descriptors of age and duration of onset of CR ("lifelong" and "late-onset"). ...


Thanks for the clarification and for the very helpful comparison between mouse and human lifespan you provided. That is the most insightful graphic I've ever seen on the topic.


So this study (PMID: 26572927subjected three groups of mice to 40% CR, one equivalent of very young children, a second equivalent to a person in their early 40s, and the third equivalent to a person around their early 50s. The young mice were sacrificed at various ages (4 + 4w), (4 + 20w) and (4 + 74w). The two older groups (48w and 68w) were put on 40% CR for 12 weeks (48 + 12w) and (68+12w) and then sacrificed. The bones of all the groups were then extensively tested in comparison with age-matched controls fed and ad lib diet.


I fear that all that's really going on with the weanlings is that they've been allowed to undergo normal childhood and (for a mouse) early adulthood skeletal growth, which while slowed continues on CR; what you're seeing in the "old" mice is the effect of CR on the bones of an organism that has completed its growth. 


Perhaps. I think you may be a little too pessimistic in your assessment. Let's look at the full-text to find out.


First off, I'll note that no effort was made to avoid micronutrient malnutrition in any of the CR groups, as they were simply fed 60% of the standard mouse chow that the AL group received:


Control mice fed ad libitum (AL) with pelleted standard laboratory chow (Ssniff R/M-H 10mm, Soest, Germany; cat. no. V154-000) and tap water served as reference groups. Food intake of five AL-fed mice housed per cage was measured once a week. From the daily eaten lab chow per AL-fed mouse the CR-fed mice received 60% once a day at 08:00 am.


I'm not sure if this is standard procedure for all CR experiments, but it seems to me when you're doing an experiment on bone health that it would make sense to ensure adequate vitamins and minerals in the CR group, through extra supplementation to match the micronutrient intake of the control group.


Second, the author's note that the life-long CR group showed better survival than the AL group, although the experiment only lasted until the life-long CR group was the human equivalent of their early 60s (78 weeks) if I'm interpreting Michael's chart correctly:


As reported previously by Kuhla et al. (12), lifelong CR-fed mice showed better survival rate and health status compared to AL-fed controls. All 74 weeks CR-fed mice reached the scheduled end of the experiments, whereas in the AL-fed group only 7 of 10 mice lived for 78 weeks.


From Michael's survival curve, it looks like 70% survival (7/10) in the AL group at 78 weeks (~20 months) is somewhat below what one would expect for well cared-for, AL-fed, C57BL/6J mice. That is a bit troubling, but let's ignore it.



The "money shots" from the paper are definitely Figures 2A and 2B, reproduced here:


They show the breaking force required to snap the femur of members of each group of mice (left) and the stiffness of the femur of each group of mice (right). Focusing on the left graph of breaking force, which is most relevant for us since we're concerned with fracture rates and risks. As you can see, in the "4+4w" group, there was an immediate and large dip in the breaking force required in the very young mice subjected to early childhood CR. 


Subsequent to that early dip, the CR mice build stronger bones throughout the remainder of the experiment, in parallel with, but never quite reaching, the level of the AL mice in terms of breaking strength (4+20w and 4+74w bars). By the end of this part of the experiment (4+74w = 78 weeks), the "life-long" CR mice are the human equivalent of early 60s. So probably not yet old enough to signs of bone deterioration with age among the AL mice. It is too bad they didn't let the experiment run longer to see if the life-long CR mice maintained their bone strength into "old age" while the AL group's bone strength declined...


But even with the data we do have, I think a strong argument can be made that even at the human equivalent of early 60s, the life-long CR mice were probably better off in terms of fracture risk than the AL mice, despite their slightly lower, although not statistically significantly so, bone strength. That's because the CR mice weighted a lot less than the AL mice throughout their lives, and especially at the 78-week mark. At that point, according to the figure below, the AL mice had gained over 50% more in body weight than the CR mice, relatively to baseline:




Given that the CR 4+74w group's bones are only marginally less strong than the AL group's, the fact that they weigh close to 50% less would suggest to me a large net benefit in terms of fracture risk from a fall, given that force = mass * acceleration (i.e. gravity). Since gravity is constant  :)xyz , the force a falling mice would experience on its bones would be proportional to its mass. With so much more mass, the extra force an AL mouse would experience on its bones during a fall would overwhelm the very modest advantage it has in bone strength relative to the CR mice, resulting in a higher fracture risk for the AL mice.


Now looking at the right side of Figure 2A above - the bone strength of adult-onset CR mice relative to AL controls, which is much more relevant to us, since all of us started CR sometime in adulthood, after we'd reached our full stature.


Again, we see in 2A that the femur breaking strength of the 48+12w and 68+12w mice subjected to "short-term" CR (12 weeks, which from Michael's chart equates to about 6 years in humans) is somewhat reduced, although not statistically significantly so, relative to the AL controls. The same was true for bone mineral density in the femur and L4 lumbar spine (Figure 4, not shown) - modest reduction in BMD in the adult-onset CR mice relative to AL controls.


If we again normalize for body weight as we did for the life-long groups, the reduced body weight of the adult-onset CR mice (-25% in the case of the 68-week onset mice!), would more than make up for the slight reduction in bone strength, making the adult-onset CR mice less prone to fracture from a fall than their AL equivalents, due to reduced impact force.


So overall, while Michael struck a cautionary tone in his interpretation of the results of this study, I find it pretty encouraging wrt CR and bone health / fracture risk. And that is independent of the author's histological finding that the bone microarchitecture of at least the early-onset CR mice was improved relative to the AL group - i.e. a lot lighter but still strong.


The authors seem to concur with my relative optimism. Here are a several quotes from the full text:


Overall, the results of biomechanical analysis points towards the hypothesis that femora show a lifelong capability to react to CR-based minor nutrient supply, since CR had little influence on bone strength or stiffness.


Lifelong CR starting at the age of 4 weeks retarded (femora, 4+20w CR vs. AL) or even completely inhibited (L4, 4+20w & 4+74w CR vs. AL) age-dependent trabecular bone loss. Moreover, our findings point towards a stimulatory effect of CR especially on axial bone formation. The increasing SMI (Structure Model Index - a measure of bone quality) values in combination with an enhanced trabecular number most likely indicate possible structural rearrangements which in turn might be due to a compensatory process in response to lifelong CR started in early age. The enhanced trabecular number and possible structural rearrangements as indicated by increase of SMI values might be due to a compensatory process in response to lifelong CR started in early age. This effect was not detectable when CR was started in adult out-grown mice. In these [adult-onset CR] animals, 12 weeks of CR had no remarkable effect on almost all bone parameters, indicating that short-period [human equivalent of 6 years] nutritional under-supply might be innocuous for bone health.


The authors point to the possibility that if the experiment with the life-long CR mice had been allowed to continue longer, rather than sacrificing the animals at 78 weeks, the CR group may have shown an advantage in bone health relative to the AL group, even without the normalization for body weight that I did:


Likewise, beneficial effects of lifelong CR on skeletal aging have been also reported by Tatsumi and coworkers (26). Initially detected trabecular bone volume differences between CR and AL fed mice and rats after 3-9 months of calorie lowering disappeared after 1 year of age. Moreover, analysis of rodent tibiae after extension of CR to natural death revealed higher trabecular bone mass in CR mice associated with reduced bone turnover. Such a biphasic effect of CR [i.e. reduced bone mass early in life, but increased bone mass in old age relative to controls] was not seen in the present study and additional end points between 24 and 74 weeks [and it would seem to me beyond 74 weeks] are required to investigate this aspect in detail.


The authors point to a possible shortcoming of their study is undernutrition in the CR groups due to employing a food restriction, rather than a calorie restriction paradigm:


[T]he strong negative effects on bone properties after short-term CR in young mice (4+4w) might be explained by under-nutrition during growth. Our data might be biased by suboptimal calcium or phosphorus supply, since CR diet was not supplemented with vitamins or minerals.


They summarize as follows:


Thus, lifelong CR can retard age-associated trabecular bone loss whereas short-term intervention in adult mice, regardless of starting age, had no substantial skeletal benefit. Analysis of senile mice after short-term CR revealed significant cortical thinning and reduction of bone mineral density while in parallel trabeculae microarchitecture was unchanged. Hence, so far we can only speculate that short-term CR might not be suitable to mitigate human osteoporosis.


So while the bones of the adult-onset mice weren't significantly weaker after the human equivalent of 6 years of CR, particularly when normalized for reduced body weight, but nor were they dramatically improved, so the authors don't think CR is likely to be a good treatment for osteoporosis in aged people. I don't think there were many people harboring that belief...



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I'm an osteoporotic -- my DXA used to be terrible.  For several years, I injected Forteo once daily -- it improved my DXA considerably, but after over 10 years, ceased to yield significant improvement.  So, at the recommendation of my Endocrinologist, I've switched to once very 6 months injection of Prolia.  My DXA continues to improve.


BTW, I've had only two minor fractures in my life -- and according to my Orthopedist. these two minor fractures were not osteoporotic fractures.


I suspect that CR osteoporosis may not be as serious as it might appear.


BTW, because of the relevance of consideration of osteoporosis to CR practitioners, my first suggestion as a speaker at the next CR Conference was Prof. James Whitfield (retired) from the CRC (Canadian Research Council) in Ottawa, who is one of the world's leading experts on the subject.  (It's possible that he might be willing to make a study of some of us that might be revealing concerning our bone health, possibly at a higher level of expertise, than the one that has already been done.)


However, if we make an invitation to Prof. Wittfield, I don't know if he'll come.




  -- Saul

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