Research & Education

Sunlight Exposure – Benefits Beyond Vitamin D


“Public health advice has tended to concentrate on the dangers of sun exposure despite the absence of any data that increased sun exposure correlates with raised all-cause mortality.”

Wright and Weller 2015 

People sometimes like to think in extremes. When too much fat was deemed “bad” for us a plethora of fat-free products flooded the market to great popularity. Now that fat—saturated fat in particular—has been exonerated of crimes against humanity there’s a trend of people loading butter and coconut oil into their coffee or tea. And the association between excessive sun exposure and greater risk for skin cancer has made some people terrified to leave the house without a visor and a thick layer of sunscreen applied to every inch of exposed skin. But is this really the best way to approach life? Being afraid of exposure to the source of heat and light energy that quite literally makes plant and animal life on our planet possible?

According to researchers our sun phobia has had disastrous consequences. They write "Insufficient sun exposure has become a major public health problem demanding an immediate change in the current sun-avoidance public health advice. The degree of change needed is small but critically important.”

There’s an old saying “Sunlight is the best disinfectant.” And let’s not forget the song from Annie: “When I’m stuck with a day that’s gray and lonely I just stick out my chin and grin and saaaaay…the sun’ll come out tomorrow.” It seems we’ve known for a long time there’s something special about sunlight. Vitamin D synthesis is obviously a huge player but that isn’t the only thing sunlight exposure contributes to human health. 

Based on “health outcomes related to sun exposure independent of vitamin D health outcomes dependent on serum 25(OH)D levels but not vitamin D supplementation and health outcomes dependent on mediators other than vitamin D it is apparent that vitamin D supplements are not an effective substitute for adequate sun exposure.

That vitamin D supplementation often fails to induce the health benefits of regular sunlight exposure raises the likelihood that there are aspects of sunlight exposure unrelated to vitamin D synthesis which affect human health in ways we cannot currently replicate with supplements.

Vitamin D supplementation can be effective for some individuals but it’s important to balance this with supportive and accessory nutrients such as vitamin K2 particularly with regard to vitamin D’s role in calcium homeostasis. Researchers note “the expected benefits of vitamin D supplements are minimized by the potential risk of cardiovascular events and beyond. Since hypovitaminosis D status usually reflects reduced sunlight exposure the obvious primary replacement should be safe sunlight exposure and not exogenous supplements.” (Again vitamin D supplementation per se may not be not harmful for cardiovascular health but only when it’s given in isolation without consideration for other nutritional factors.)

As for aspects of sunlight independent of vitamin D activity sunlight exposure influences serotonin production in the brain. In a study that assessed serotonin metabolites in blood from healthy young men researchers found that “turnover of serotonin by the brain was lowest in winter. Moreover the rate of production of serotonin by the brain was directly related to the prevailing duration of bright sunlight and rose rapidly with increased luminosity.” Additionally ultraviolet light exposure (UV-B) was shown to increase beta-endorphin in human skin epidermal keratinocytes in vivo. Researchers speculate that this increase could be responsible for why some people seem to be “addicted” to UV exposure. (We’ve all heard the term “sun-worshipper” but this applies to those who frequent UV tanning beds as well.) 

Another positive aspect of sufficient exposure to natural light is better eyesight. Children who spend more time outdoors have a lower risk of developing myopia. We could attribute this to the possibility that children who spend more time outdoors are spending less time in front of computer screens and books and are focusing more on things in the distance but the finding of reduced risk for myopia is irrespective of how much near work they do. So maybe there’s something about the characteristics of natural light itself independent of how near or far the eyes are focusing. Chronic hyperinsulinemia is a plausible explanation for the prevalence of myopia in the current day but perhaps insufficient sunlight exposure is an additional factor. Children aren’t the only ones who might benefit from natural light.  Older people may want to rethink sun phobia and make an effort to get outdoors more as well.

“Phototherapy” seems especially helpful for skin disorders such as localized scleroderma vitiligo and psoriasis owing to mechanisms unrelated to vitamin D status. Sunlight exposure may also be beneficial for cardiovascular health in ways unrelated to vitamin D. According to one study “Skin contains significant stores of nitrogen oxides which can be converted to NO by UV radiation and exported to the systemic circulation. Human studies show that this pathway can cause arterial vasodilatation and reduced BP.”

As with seemingly anything that’s good for health sunlight exposure likely has a U-shaped curve: just because some is good doesn’t mean more is better. Adequate exposure is important but burning and blistering means you’ve overdone it.