Sunlight, Vitamin D and Cancer

They wrote in The Proceedings of the National Academy of Sciences, the benefit of moderate sun exposure seems to outweigh the risk of skin cancers.

"Assuming you go out in the sun, vitamin D increases as you get closer to the equator," explains Setlow. "The importance of vitamin D is it tends to protect against the lethal effects-- death from the cancer… not just skin cancers."

It's more evidence that a little sunshine can boost more than your spirits.

The researchers say that because cancers take so long to appear, it will take many years to know whether recent anti-sun campaigns may actually cause an increase in the deadliest form of skin cancer, malignant melanoma.

Setlow explains how that could happen. "Vitamin D is made by the shorter wavelength of sunlight, what we call ultraviolet B, or UV-B," he says. But, scientists have only recently understood that "Melanoma is caused by the longer wavelength… UV-A."

While UV-B rays can cause nonmelanoma skin cancers by damaging DNA, those cancers don't tend to be lethal. "The kinds of cancers we call melanomas may result in death if not attended to, but vitamin D protects against death from many types of skin cancers and many other (internal) cancers-- breast cancer, prostate cancer," he says "So you don't want to get too much UV-A, but you want to get UV-B."

The problem, explains Setlow, is that conventional sunscreens generally give us the opposite. UV-B rays are the ones that cause burning, while UV-A rays cause tanning. "Most conventional sunscreens screen out UV-B but not UV-A," he points out.

That's why more researchers are recommending moderate sun exposure of 10 to 15 minutes in the sun, followed by using a sunscreen that blocks both UV-A and UV-B. But the emphasis is on moderate, and many dermatologists still disagree.

Setlow also suggests that sunscreens be redesigned in light of the new understanding of the effects of the different UV wavelengths.

But he also reminds us that we can also get vitamin D from foods or supplements.

"You're getting a benefit that tends to decrease the death rate from cancers; Cancers in general, not just skin cancers," he says.

This research was published in PNAS advance online publication the week of January 7, 2008, and funded by: Sigval Bergesen D.Y. og hustru Nankis Foundation, the Research Foundation of The Norwegian Radiumhospital and by Helse-Sør Norway. BNL is operated by Brookhaven Science Associates, under contract with the US DOE.