Danny ChaiI will probably get chastised for this entry, rightly by Sandra, wrongly by Rob, but whatever. The rest will find it boring.
I’m OK with moderate (emphasis on moderate) sun exposure. Without sunscreen. Not just OK – I think it’s a good thing. Main reason being that it prevents Vitamin D deficiency.
I feel comfortable saying that vitamin D deficiency is caused by inadequate sunlight exposure. That is the cause. When our skin is exposed to sunlight, it produces vitamin D. Looking at both the geography of diseases related to vitamin D deficiency and high risk groups, it’s directly linked to sunlight exposure.
For example, look at rickets, a disease linked to severe vitamin D deficiency. High risk groups are dark-skinned people, people who stay indoors all the time, and people who live in cities. Do a search on the history of rickets, and you’ll find that rickets was relatively rare until the Industrial Revolution. It reached an apex in the late 1800s, 1900s, and it’s attributed to smog and people living in cities where their exposure to sunlight was limited. Even today (do a search on the geographical distribution of rickets), cases of rickets in developing countries is clustered around cities (in ratios far greater than the population distribution).
In a separate discussion, it was suggested that rickets is caused primarily by malnutrition. But the statistics don’t back that up. If most people got enough sunlight exposure and the difference was nutrition, you would expect for rickets to have been common in history and to be increasingly rare, especially in more developed nations, as nutrition got better. You would also expect that cases of rickets be linked to areas of poor nutrition. That’s not what you see, as mentioned above. It became more common in the past couple centuries due to influences that limited sunlight exposure, and only stopped when we started fortifying our milk in the 1930s. And in fact, the UK Department of Health announced in December that rickets is currently on the rise around the world, especially in the United States, Canada, and northern Europe. That can’t be explained by malnutrition. Better vitamin supplementing can help deal with it, but the cause is inadequate sunlight exposure. Any discussion of rickets (and vitamin D deficiency in general) that meaningfully looks at the statistics must mention inadequate sunlight exposure as a primary cause.
In short, people around the world with poor diets who get lots of sunshine are not at risk of vitamin D deficiency, whereas people who have decent diets but don’t get enough sun tend are at risk of vitamin D deficiency. By decent diet I mean a balanced diet without supplements. A normal diet, even a healthy one, isn’t enough, because few foods are high in vitamin D. It’s enough of a problem that the American Academy of Pediatrics recommends vitamin D supplements for all breastfed infants (who don’t get vitamin D fortified milk) and kids who don’t get enough sun. (Note: that same AAP guideline acknowledges “that most vitamin D in older children and adolescents is supplied by sunlight exposure” and that “Sunscreens markedly decrease vitamin D production in the skin.”)
I’m not saying if you don’t get enough sun you’ll get rickets. That’s just an extreme case. There are other diseases indirectly linked to vitamin D deficiency. For example, the geography of the incidence of colon cancer closely maps to that of rickets (which again, is closely related to sunlight exposure). This journal concludes that the “evidence is ‘fairly compelling’ that sunlight and vitamin D are protective.”
I’m not sure if I’m making my point, but I think it’s that the data suggest that modern (last 200 years) life has made it such that we don’t get enough sunlight exposure to get enough vitamin D. Thus, we need to supplement our diets with extra, e.g. with vitamin D fortified milk or with pills so that we avoid diseases like rickets that, until recently (last 200 years), were rare. Even with supplemented milk, vitamin D related diseases are on the rise in the U.S. (including rickets in the Bay Area).
The obvious solution is to get a little more sun, without sunscreen, since even sunscreen of SPF 8 can block vitamin D production by 95%. But that’s rightly controversial because of the skin cancer risk (and why I say Sandra will legitimately chastise me). Thus even though the scientific bodies like the AAP recognize that sunlight is the primary source of vitamin D, their official recommendation is for nutritional supplements.
Nevertheless, I try to go the sun route for several reasons. One, I don’t drink milk (lactose-intolerant). Two, I’m sporadic in taking vitamin supplements. Three, I sit indoors all day and mostly all night. Four, skin cancer in Asians is fairly rare. Five, I’m not sure vitamin D supplements are as good as sun. Even though epidemiologically, there is a strong suggestion that sunlight and vitamin D help prevent colon cancer, a NEJM study found that taking vitamin D supplements made no difference in colon cancer incidence after 7 years.
Therefore, balancing the different risks, it seems best for me to get a few minutes of sun when I can. For someone like me, I think it’s more likely that I get not enough sun than too much. Again, too much sun is obviously bad. But the data suggest that lots of people in this country don’t get enough, so much so that they keep recommending more supplementing. So being too crazy about blocking all sun exposure is not without its risks either.
Rob will discount this entry because he only accepts as valid sources articles from Science and Nature, listing Jesus as a co-author. Oh well. One more random references for him to ignore: From India – “Indirectly, the most plausible explanation for rural children escapting rickets in the face of greater poverty and insanitary conditions in villages, as compared with those of the city dwellers, may seem to lie in the protection afforded by sunshine.”
Boring.