Sunshine .... for health and longevity ??? (New Scientist, 16 March)

[KHashmi317]

LET THE  SUN SHINE [COVER STORY]
 For years, we were told to slather on sunscreen   to prevent skin cancer . But does blocking out   the sun do us more harm than good?  
 Linda Geddes investigates
 16 March 2019 | NewScientist | 29
SLIP! Slop! Slap! As public-health  campaigns go, Cancer Council Australia's  dancing seagull telling people to slip on  a shirt, slop on some sunscreen and slap on a  hat must rank among the stickiest in history. 
Launched in 1981, it prompted many a  devoted sun worshipper to reconsider  whether a "healthy tan" was virtuous, or a  herald of premature skin ageing and cancer. 
It seems to have been effective: after  increasing in the general population for  decades, rates of the deadliest form of skin  cancer, melanoma, are now falling among  Australians under the age of 40. "These are  people who will have been exposed to the 
[Slip, Slop, Slap] message for pretty much    their whole lives," says Heather Walker of  Cancer Council Australia. 
But has this come at a cost? In Australia  and worldwide, the prevalence of vitamin D  deficiency is increasing - and sunscreen  has taken much of the blame. Low levels of  vitamin D are associated with weaker bones  and teeth, infections, cardiovascular disease  and autoimmune and inflammatory diseases  including multiple sclerosis. And although  vitamin D supplements have been touted as  a solution, so far they don't seem to have the  effect that was expected. Now evidence is  accumulating that sun exposure has benefits  beyond vitamin D.  All of this has prompted some to label  sunscreen "the new margarine" - a reference  to health advice in the 1980s and 90s to  switch from butter to hydrogenated vegetable  oil to protect heart health, only to discover  that the trans-fats found in many margarines  were potentially more harmful. Could  sunscreen face a similar fate? And if sun  exposure is necessary, how do we reap the  benefits without getting skin cancer? 

The Ancient Babylonians, Egyptians,  Greeks and Romans all recognised that  sunlight could be harnessed to promote  health. Hippocrates, for instance, believed    that it was beneficial in the treatment of most  ailments. But medical interest in sunlight  truly took hold at the turn of the 20th century,  following observations that it kills bacteria  and that a deficiency is associated with rickets,  a condition that affects bone development  during childhood. By the late-1920s, sunlight  was being touted as a cure for pretty much  every illness under the sun, and a suntan had  become an emblem of health and status. 
Soaking up rays
 It was also around this time that scientists  identified one of the key mechanisms by which  sunlight promotes health. When the ultraviolet  (UV) B rays in sunlight hit the skin, they spur  the synthesis of vitamin D3. This circulates in  the blood before being further metabolised  into the active form of vitamin D elsewhere in  the body. Bone and muscle cells use vitamin D  to regulate levels of calcium and phosphorus,  keeping them strong and healthy - but it is  also important for certain immune cells,  which spew out an antimicrobial in response  to it. Indeed, last month a study found that  giving vitamin D supplements alongside  antibiotics could speed up treatment of  multidrug-resistant tuberculosis in the lungs. 
Of course, sunlight also has a dark side. This  was recognised in 1928 by British researcher  George Findlay, who exposed mice to regular  irradiation with UV light and observed that  tumours developed on their skin. Since then,  many more studies have shown that UV light  triggers DNA mutations in our skin cells,  potentially leading to cancer. Sunscreen,   in combination with other sun avoidance  measures, reduces that risk. 
Today, the sunscreen industry is booming. 
Global sales of sun-care products totalled  around $15.8 billion in 2015 and are projected  to reach $24.9 billion by 2024. There is also a  trend towards ever higher sun protection  factors, even SPF100, although they don't  necessarily provide much extra protection  (see "Sunscreen myths", page 29). Combined  with the fact that most Westerners spend a lot  of time indoors - in the US it is, on average,  90 per cent of their lives - this has prompted  concerns that, at least at high latitudes, many  people aren't storing enough vitamin D to see  them through winter. The fear is that their  bones, muscles and possibly other tissues are  suffering as a result. 
-You don't need to  sizzle in full sun to  make vitamin D ---

 About 10 per cent of people in the UK have  insufficient levels of vitamin D during the  summer, rising to nearly 40 per cent during  the winter months. For this reason, in 2016,  the UK's Scientific Advisory Committee on  Nutrition recommended that everyone   should consider taking vitamin D  supplements during winter, because there is  good evidence that they can make a difference  to bone and muscle health.
The trouble is, in recent years the list of  illnesses associated with vitamin D deficiency  has grown to include cardiovascular disease,  infections and even infertility, but for many  of these, supplements don't seem to lead to  better health. Several recent studies actually  associated high doses of vitamin D with an  increased risk of falls in older people. 
According to a recent review of trials,  apart from bone-related conditions,there  is good evidence for only two things: that  vitamin D can prevent upper respiratory tract  infections and stop existing asthma from  getting worse. Ongoing trials may yet find  additional benefits, but it is unlikely  vitamin D will be a panacea for our many  modern health challenges. 
Vitamin D isn't the only way sunlight affects  our health, however. UV light itself may also  help marshal our immune system via the  largest organ in the body: our skin. Long  thought to be simply a protective barrier that  provides a way to sense our environment,  it turns out our skin may also be a vital part  of the immune system. The outermost layer  contains cells called keratinocytes that absorb  UV light, then send signals to regulatory cells  that help to keep the immune system in check. 
If there is plenty of UV light, these dampening  signals are transmitted to the rest of the body,  suppressing its immune responses. 
One idea for why, as daytime creatures on  this sunny planet, we evolved this response  to the sun is that it is a way to tolerate our  own cells, rather than misidentifying them  as "foreign" and destroying them. By getting  sunlight, we boost that tolerance of self,  which is essential for preventing autoimmune  diseases, says Scott Byrne, an immunologist  at the University of Sydney. 
 Protection factor 
 Byrne has been working with Prue Hart at the  University of Western Australia to investigate  whether UV light could help people with  multiple sclerosis (MS), an autoimmune  condition that is more common at higher  latitudes. Hart has shown that exposing  mice to UV doses equivalent to a brief stint  in the midday sun can prevent them from  developing a form of MS. Now she and Byrne  are looking into whether UV exposure from  specialised lamps could slow, or even prevent,  the development of MS in people.  
 However, sunlight's effect on immune  suppression also has a big downside:  "Probably the reason why skin cancers grow  is because the immune system is dampened  and less efficient," says Hart. 
Even so, immune suppression can't explain  all the effects of sunlight on health that we  have seen. Consider the perplexing finding  that people with high sun exposures have  higher life expectancies, on average, than  sun avoiders - despite facing an increased  risk of skin cancer. 
That was the discovery of a large Swedish  study into the risks associated with melanoma  and breast cancer. In 1990, nearly 30,000  women were interviewed about their health  and behaviour - including their sun habits. 
They were then interviewed again 20 years  later. When Pelle Lindqvist at the Karolinska  Institute and his colleagues crunched that  data, they found that, on average, women  who spent more time in the sun lived one  to two years longer than sun avoiders, even  after adjusting for factors such as disposable  income, education level and exercise.    That suggests it wasn't simply about having a  more healthy lifestyle overall. The researchers  found this reduced life expectancy among sun  avoiders was mostly due to a greater risk of  death from cardiovascular disease and other  non-cancer-related illnesses, such as type 2  diabetes, autoimmune disease or chronic    lung disease. What could be going on?  Richard Weller at the University of  Edinburgh, UK, thinks he has the answer. Like  most dermatologists, Weller started his career  believing that sunlight is terribly bad for you. 
He still wouldn't dispute that it is a major risk   factor for skin cancer. However, his discovery  that we produce and stockpile vast quantities  of nitric oxide - a potent dilator of blood  vessels - in our skin, which can be activated  by sunlight, made him think again. 
He wondered if this UV-activated nitric  oxide was why people's blood pressure  readings are lower in summer than in winter,  and whether it may help to explain why  cardiovascular disease is more prevalent at  higher latitudes. If that were the case, it would  also help to explain the puzzling results of the  Swedish study. What he found pointed in that  direction: his experiments showed that if you  expose somebody to the equivalent of about  20 minutes of UK noontime summer sunlight,  they experience a drop in blood pressure that  continues even after they step indoors. 
This sunlight-activated nitric oxide may  have other functions as well. Separate studies  have revealed that mice fed a high-fat diet that  has been shown to promote weight gain and  metabolic dysfunction can be protected  against these effects through regular exposure  to UV light, but not if nitric oxide production  is blocked. Nitric oxide is implicated in  wound healing, not to mention achieving  and maintaining an erection. It also seems  to be another substance to which regulatory  immune cells respond. 

---"  People with high    sun exposures    have higher    life expectancies,    on average, than    sun avoiders"----

 More evidence will be needed to convince  the wider dermatology community to step  back into the sunlight. "The only established  benefit of solar exposure is vitamin D  production; others are still controversial,"  says Antony Young, who studies the effect  of solar UV on the skin at King's College  London. Even so, he believes there may be  something to Weller's findings: "UV has  an awful lot of effects at a cellular and a  molecular level, and it would certainly not  be surprising if these had been exploited by  evolution to get some advantages."  All of this leaves health policy-makers  with a dilemma. Most still believe that the  need to protect skin from sun damage  outweighs the risk of vitamin D deficiency,  given repeated findings about skin cancer. 
For example, getting sunburnt once every  two years has been found to triple a person's  risk of developing melanoma. 
Cancer Council Australia now emphasises  the importance of the UV index - a measure  of how strong the sun's UV rays are on a scale  of 1 to 11 - in dictating when sunlight should  be avoided. Together with other Australian  medical bodies, it recommends staying  indoors when the UV index is 3 or above,    or following the modified Slip, Slop, Slap,    Seek and Slide message if you are outdoors for  more than a few minutes (the latter two were  added in 2007, to emphasise the importance > of seeking shade and sliding on sunglasses).  Sunscreen is a last resort. "You should use  clothing to cover up," says Walker. "That  offers the most reliable protection. Only use  sunscreen on the parts of your skin that are  uncovered." During autumn and winter,  though, the council encourages people living  in Southern Australia, where vitamin D  deficiency is more of a risk, to head outside  with some skin uncovered in the middle  of the day, when the UVB rays needed to  synthesise vitamin D are at their strongest. 
That won't work in countries at higher  latitudes, such as the UK, because the sun  doesn't rise high enough during winter for  the UVB rays to reach ground level. Populations  in these countries are dependent on the  vitamin D they stockpile during sunnier  months, supplemented by that obtained from  foods such as oily fish, egg yolks and some  breakfast cereals, or taking vitamin D tablets. 
You don't need to spend hours sizzling  in the summer sun to ensure you synthesise  adequate vitamin D for the year (see diagram,  page 31). "We still don't know the minimal  dose requirement [of sunlight] for adequate  vitamin D production, but whatever it is,    it is very much lower than is necessary to  have a sunburn," says Young. 
You can even manufacture some vitamin D  while wearing sunscreen - although the  amount you make will be reduced. But  preliminary studies by Weller suggest that  sunscreen inhibits both the release of nitric  oxide and vitamin D.

----Smearing on  sunscreen should   be a last resort after  covering what you  can with clothing -----

 So, what does he tell his patients? "I am  conflicted," Weller says. "Sunlight is good and  bad." Both he and Young stress the importance  of knowing your skin type: people with darker  skin will need to spend longer in the sun to  generate vitamin D and nitric oxide, and it  also takes longer for them to burn. 
Possibly, though, there is a way of getting the  best of both worlds. Weller and his colleagues  have recently patented an ingredient that  could be added to sunscreen, and which  releases nitric oxide into the skin when  sunlight hits it. He has had little interest from  sunscreen manufacturers, though, possibly  because it makes things more complicated. 
"They have spent years and years - as has the  dermatology community - saying sunlight is  bad: avoid it," says Weller. "Now we're coming  along with a more nuanced message."  ¦
 Linda Geddes is a New Scientist consultant and the  author of Chasing the Sun: The new science of  sunlight and how it shapes our bodies and minds

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Infographic:
How much sun? The number of minutes you need in the sunshine to get your daily dose of vitamin D depends  on your skin colour, where you are and the time of year

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 SUNSCREEN  MYTHS    1

Being in the sun is safe if you  are wearing sunscreen "Sunscreen is a screen, not a block,"  says Heather Walker, chair of Cancer  Council Australia's national skin cancer  committee. "There will always be some  UV that gets through." SPF30, for instance, allows 3.3 per  cent of UV through. With SPF50 it is 2 per  cent, and with SPF100 it is 1 per cent. 
However, that assumes you are applying  it properly: using roughly a teaspoon for  each limb, plus one each for the front  and back of the torso, and another for  the face and neck, and reapplying every  2 hours. Most people apply less than  three-quarters of this amount, and don't  reapply often enough. 
 And the SPF rating applies only to UVB  rays, not to UVA rays, which also damage  skin. For decent UVA protection, look for  sunscreens labelled "broad spectrum  protection"; with a symbol of UVA in a  circle or with a high UVA star rating. 
---
 SUNSCREEN  MYTHS                                   2 
 I get plenty of sun exposure  walking to and from work -   I can't be vitamin D deficient To make vitamin D, you need exposure  to UVB rays, which peak around noon. 
You make relatively little vitamin D in  the morning and late afternoon when  the sun is lower in the sky. "If you want  to top your vitamin D up, the best thing  to do is just get a few minutes [of sun  exposure] at noon," says Antony Young  at King's College London. 
There are still benefits to getting  outdoors during the morning and  afternoon however: exposure to bright  daylight helps to strengthen our  circadian rhythms. These 24-hour  cycles in our biology and behaviour  help us to feel sleepy and alert at the  right time, among other things.

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 SUNSCREEN  MYTHS                                   3

 You can make vitamin D by  sitting next to a window   Not if the window is shut, because UVB  rays struggle to penetrate glass. You can  burn, however, because some UVA rays  can get through and these can cause  skin damage.

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[KHashmi317]

About that  Swedish longevity  study (as with almost ANY health study), I'm not sure how you could  "adjust [...] for factors such as disposable  income, education level and exercise..." 

E.g., being outdoors on a sunny day has positive psychological effects (lifts your spirits, etc). There may be MANY other unaccounted-for factors. 

[Todd Allen]

Nice graphic which reinforces my belief/experience that I gain useful sun exposure in winter living in Chicago - at least on sunny days which are somewhat rare and tend to be very cold.  Spent a couple hours in mid day sun a couple days ago wearing shorts and got a touch of pinkness on my legs.

[KHashmi317]

An important miss in the NewSci article is importance of protecting eyes from sunshine. Don't forget the shades!

[mikeccolella]

Yeah I knew this was gonna happen sooner or later. Scientific types can get really bogged down in the research and draw conclusions that are just not rationale!

[mccoy]

Eritema is believed to be a good qualitative measure of potential damage from sun exposure. Sgnificant eritema should be avoided, so progressive exposure and very brief at first especially for the fair skinned ones

[LizC]

This doesn't answer (or even ask) the question of what to do when it's already "too late": what about those of us who've already suffered severe sun damage and been diagnosed with skin cancers? Is there any level of sun exposure that's beneficial, or even safe for us? 

I grew up in Florida before effective sunscreens were invented, and spent my childhood and teen years out on the beach year-round. I'm paying for it now. In December of 2018 I had a melanoma removed from my right dorsal forearm along with a sentinel lymph node biopsy (all is well), and in a few weeks I'll be having Mohs surgery for a squamous cell carcinoma in situ on the superior helix of my left ear. This could involve removing up to 1/3 of the ear tissue (do NOT google this if you're at all squeamish!!!) and reconstructing a new ear from a skin graft. I've also undergone multiple uncomfortable treatments for actinic keratoses (cryosurgery, topical fluorouracil, blue light therapy). Needless to say, I don't want to increase my risk of recurrence, or develop new cancers, or incur additional cosmetic damage. 

I've read a lot of the current research, and there doesn't seem to be a 100% firm consensus. Right now I'm leaning toward erring on the side of caution with zinc oxide, long sleeves, and wide-brimmed hats while taking vitamin D supplements. I guess I'm just feeling particularly frustrated and annoyed right now because a co-worker spent ten minutes in my office this morning explaining to me how "according to Dr. Mercola, sunscreen is the cause of melanoma."  I'm pretty low on patience when it comes to Mercola and his fecal matter of bovines, but it's hard to counter when there's still so much conflicting and missing evidence from science itself.

[Gordo]

I found a great resource that I have been using to determine how long I can safely sit out in the full sun with no shirt on:

https://sunburnmap.com/

 

[mikeccolella]

Another point, according to Michel Horlick a sun exposure proponent and vitamin D researcher is  to watch your shadow. When it’s your height or less that indicates adequate sun rays for efficient vitamin D production. I would assume it would work for nitric oxide etc. A simple method for sure. Here  in Pittsburgh Pa. you can even get this as early as March and as late as November but the hours are very limited of course in those two months. But it’s so simple and I can be outdoors and simply know by looking at my shadow.

[JayR]

" I would assume it would work for nitric oxide" - is that really the case.   As vitamin D and NO production are through entirely different mechanisms they could require very different UV wavelengths and intensities to produce them.  Does anybody know of any research about NO production and characteristics of the UV required?

[Sibiriak]

 

 

Sun Exposure and Its Effects on Human Health: Mechanisms through Which Sun Exposure Could Reduce the Risk of Developing Obesity and Cardiometabolic Dysfunction

Naomi Fleury, Sian Geldenhuys, and Shelley Gorman^*

Int J Environ Res Public Health. 2016 Oct; 13(10): 999.

Published online 2016 Oct 11. doi: 10.3390/ijerph13100999

PMCID: PMC5086738 PMID: 27727191

Excerpt:

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7.5.2. UVR-Induced Nitric Oxide

Skin exposure to UVR triggers the release of nitric oxide from dermal storage sites into the blood stream [110], which can be measured by increases in serum nitrite [111,112] (Figure 4). Anti-hypertensive and vasodilatative effects are induced by treatment with nitric oxide and compounds that increase local levels of nitric oxide-related metabolites, such as nitrite or nitrate [110,113]. Whole-body irradiation of healthy adult volunteers to UVA radiation reduced blood pressure in healthy young adult males, which was sustained for 30 min. These effects were associated with an increase in circulating nitrite [111]. The effects of UVA radiation were independent of nitric oxide synthase, suggesting a role for the release of preformed nitric oxide stores from cutaneous tissue through the alternate nitrate-nitrite nitric oxide pathway. Nitric oxide induced by eye exposure to UVR can suppress immunity in a systemic fashion [114,115].

 

 

Figure 4

Mediators other than vitamin D are produced or released by exposure to UVR and may play a role in reducing weight gain and signs of cardiometabolic dysfunction. Exposure to ultraviolet radiation (UVR) results in the production of heme oxygenase, which causes the breakdown of heme, catalysing the production of carbon monoxide (CO), iron (Fe) and biliverdin; however, the role of this pathway on the development of obesity and cardiometabolic dysfunction is still to be defined. Nitric oxide stores in skin are released into the blood stream as nitrite potentially reducing blood pressure and increasing vasodilation. When skin and the eye are exposed to UVR there is a release of α-melanocyte-stimulating hormone (MSH), which activates pro-opiomelanocortin (POMC)-responsive neurons in the arcuate nucleus of the hypothalamus, and hypothetically could reduce appetite and food intake.

Our studies suggest that UVR-induced nitric oxide can have benefits for the control of the cardiometabolic dysfunction associated with obesity. To demonstrate a role for UVR-induced nitric oxide, a nitric oxide scavenger (2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt, cPTIO) was applied to irradiated skin immediately following exposure to UVB radiation (1 kJ/m²) also administered to mice fed a high fat diet [75]. As an alternative to UVR, some mice received a topical treatment twice a week with a nitric oxide donor (S-nitroso-N-acetylpenicillamine, SNAP). The UVR or SNAP treatments (alone) increased skin nitric oxide levels 5 min after skin exposure, while cPTIO treatment post-UVR reduced skin nitric oxide levels. In mice fed a high fat diet, the SNAP treatment reduced mouse weights and the development of insulin resistance, while topical cPTIO reversed some of the positive effects of UVR, specifically, fasting glucose levels and hepatic steatosis; suggesting that some of the benefits of UVR may be dependent on skin release of nitric oxide [75]. Results from other rodent studies suggest that dietary nitrate causes browning of WAT and increased expression of thermogenesis (heat production)-related genes in brown adipose tissue [116], providing a mode of action through which dietary nitrate has anti-obesogenic effects [117]. Other studies support the notion that increasing the bioavailability of nitric oxide may have benefits for obesity, with reported benefits of nitrate-rich supplements in reducing circulating triglyceride levels [118]. However, the relationships between obesity and nitric oxide are complex, where bioavailability of nitric oxide may be reduced in obese individuals compared to healthy age- and gender-matched counterparts [119], and excessive expression of nitric oxide (known as nitrosative stress) is associated with tissue inflammation in conditions like NAFLD [120].