Good news for tanning salons - sunlight and health

New research lauding the benefits of sunlight, and not because of vitamin D, brings up a general question about reductive research.  The work was reported in Edinburgh at the International Investigative Dermatology 2013 meeting, and suggests that sunlight helps reduce blood pressure, which leads to lower risk of heart attack and stroke.

Researchers found that UV rays from the sun caused their study subjects to release a compound that has this positive effect on blood pressure.  That's nitric oxide, apparently, which is released into the circulation when sunlight touches the skin.  The researchers note that hypertension and cardiovascular disease rates rise in the winter, and propose it's because of reduced exposure to sunlight.

And, Medical News Today quotes the lead author:

Richard Weller, Senior Lecturer in Dermatology, and colleagues, say the effect is such that overall, sun exposure could improve health and even prolong life, because the benefits of reducing blood pressure, cutting heart attacks and strokes, far outweigh the risk of getting skin cancer.

It's of course notable that these results are being presented at a dermatology meeting, because dermatologists have been telling us for years to reduce our exposure to sunlight, a prime cause of skin cancer.

La promenade (1875) by Claude Monet

Whether these results are valid or not is not our interest here.  Indeed, hypertension is high among African Americans and Afro-Caribbeans, though the data are equivocal for Africa itself. 

But, ok, let's assume there's something to this.  Indeed, let's assume that even a tenth of what people say about vitamin D is true, and that exposure to sunlight is good for our health for multiple reasons.  And that wouldn't be surprising, given that we've lived most of our evolutionary history exposed to sunlight, and if it were as bad for us as dermatology says it is, we'd not have made it this far.

That aside, this brings up the question of competing effects.  Sun exposure is bad because it causes cancer.  No, it's good because we need the vitamin D, and now the nitric oxide.  Red wine in moderation is good for us because it lowers heart disease risk, but it's bad because it causes breast cancer.  Eating fish is good because of antioxidants, but bad because of mercury.  Brown rice is good because it's a source of fiber and vitamins, but bad because it's loaded with arsenic. 

The list could, and does, go on and on.  In large part it's a product of reductive science, looking at single factors and determining single outcomes, ignoring complexity and context.

And life is a balancing of costs and benefits -- exercise is good for us, but running wears out knees, and bicycling brings risk of accidents.  You might decide that the benefits outweigh the costs, but how informed is that decision, really?  How do you decide whether or not to lie in the sun?  You might not in fact be at risk of hypertension, so sun exposure isn't a great benefit to you in terms of lowering your risk of heart disease, and so the potential cost of skin cancer might be greater for you than the benefits.

But, how would you know?  These results are based on population data, measuring only a subset of factors that are actually involved in the complex interactions that result in hypertension or skin cancer or breast cancer or heart disease, and certainly not measuring your personal set of factors, exposures and risk.

In the end, we probably should make these lifestyle and dietary decisions based less on this week's data -- indeed, a lot of the relevant data we don't have and don't even know we should have -- but on how much we enjoy that glass of wine, or lying in the sun.