It's a health conundrum that doctors have been trying to resolve for several years now: most Americans are deficient in vitamin D, which can help to build bones and even protect against certain cancers and autoimmune diseases such as multiple sclerosis, but the most efficient source of D, the sun, can also trigger skin cancers.
That means that skin cancer patients might be at even greater risk of having insufficient amounts of vitamin D, since they are instructed by their doctors to avoid the sun's cancer-causing ultraviolet rays. A study led by Dr. Jean Tang at Stanford University found that, indeed, skin cancer patients may be three times more likely to be vitamin D deficient than the general population. And the results also raise interesting questions about whether such shortcomings may be responsible for their cancer, or are a consequence of it.
Tang and her colleagues studied 41 patients with a rare genetic form of skin cancer that predisposes people to develop many skin cancer lesions over their lifetime. Over the two-year study period, the scientists measured the blood levels of a common vitamin D metabolite in the volunteers every three to six months. Not surprisingly, in order to avoid recurrent growths, most of the subjects used sunscreen daily, and avoided extended periods of sun exposure. While the mean levels of the D byproduct for the American population is 27.5 ng/ml, these skin cancer patients averaged 24.5ng/ml. “Even though you say the general population is at high risk of vitamin D deficiency, these skin cancer patients are at even higher risk,” says Tang.
At the moment, experts don't have a target “healthy” range of vitamin D in the blood, but a government panel is expected to provide more guidance on such a threshold in November. Until then, doctors generally advise their patients to take at least 200 IU to 400 IU of vitamin D daily, in supplement form. As for spending more time in the sun, physicians can't advise patients on how much sun is safe. “There isn't an easy answer,” says Tang. “But the safest recommendation is that some amount of sun exposure, such as what you would get by exercising outside or walking to your car or walking to work, is always reasonable. But it would be foolish to say go out and get a lot of sunlight to boost your vitamin D levels because sunlight is still a risk factor for skin cancer.”