Vitamin D, the Sun, and the Skin

There is an ongoing controversy regarding purported benefits of sun tanning—which produces vitamin D in the skin.  Vitamin D is a necessary nutrient, and some claim it may reduce the chance of getting some cancers.  But sun exposure causes skin cancer, which accounts for over half of all cancer in the United States.  

Vitamin D is also obtained from diet; breakfast cereals, fatty fish, fortified milk and orange juice, and vitamin supplements. 

There is a simple solution; protect your skin from the sun—especially if you are fair or have ever burned, and eat Vitamin D.  That way, skin cancer risk is minimized and vitamin D levels stay adequate.  

So why is there a controversy?  It seems that some media and a few researchers are creating one for attention.  Also, the tanning industry, which benefits from irradiating its patrons, clings to the long-refuted claim that tanning is healthy.

As nature intended, those least susceptible to Vitamin D deficiency are most at risk from UV rays: young adults with light skin.  Light skin most efficiently produces Vitamin D, and equilibration takes place after limited, incidental sun exposure.  Whole body tanning overdoes it drastically.

Low levels of vitamin D lead to bone problems: rickets and osteomalacia (bone softening).  High levels of vitamin D are toxic, leading to hypercalcemia, hypertension, and kidney failure.  Appropriate levels are in between, but unknown.  Moreover, vitamin D is fat soluble, so levels stay rather constant.

Recommended blood level of Vitamin D has been arbitrarily set at 75 nmol/L (nanomoles per liter).  Yet a recent study showed that 51% of young, healthy, tanned surfers and skateboarders in Hawaii with an average of over 22 hours of sun exposure a week had lower levels.  So it seems that even lengthy sun exposure is insufficient to raise levels above a "cut-off."

Though epidemiologic studies have suggested that low vitamin D levels are a risk for colon cancer, no well-done study has ever shown this to be the case.  Indeed, a recent prospective, randomized, placebo-controlled trial (the "gold standard" of research) of vitamin D supplementation for over 7 years showed no relation between colorectal cancer risk and total vitamin D intake or amount of sun exposure. 

Likely, many patients with colon cancer also have “low” vitamin D levels.  But as explained above, an adequate level of vitamin D is arbitrarily set.  Place the bar high enough, and almost everyone will fail to clear, including those with cancer.

This controversy is really not one at all.  The choice is easy.  Eat a diet with vitamin D, and protect yourself from a known cause of cancer; ultraviolet radiation. 

-----

An excellent (though lengthy) article on the subject is by Barbara Gilchrest. Sun exposure and vitamin D sufficiency.  The American Journal of Clinical Nutrition 2008;88 (suppl):570S-7S. 

The (abstract) cited regarding surfers and skateboarders is Binkley et al.  Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab 2007;92:2130-5.

The colon cancer and vitaming D supplement article is:  Wactawski-Wende et al.  Calcium plus vitamin D supplementation and the risk of colorectal cancer.  N Engl J Med 2006;354:684-96.