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Sunlight: Good or Bad for Cancer Risk?

Brief Sun Exposure Produces Vitamin D, May Protect Against Non-Skin Cancer Deaths
By
WebMD Health News
Reviewed by Louise Chang, MD

Jan. 7, 2008 -- If you are deficient in vitamin D, getting a little sun may actually reduce your risk of dying from certain non-skin cancers, according to a new report. And that benefit may outweigh the risk of getting skin cancer.

When it comes to reducing the risk of dying from internal cancers, "sun exposure is good for you," says Richard B. Setlow, PhD, senior biophysicist emeritus at the U.S. Department of Energy's Brookhaven National Laboratory in Upton, N.Y. He is a co-author of the study, along with scientists from Norway's University of Oslo and the Institute for Cancer Research in Montebello.

Sunlight triggers production of vitamin D, which in turn has been shown to help reduce the risk of dying from breast, colon, prostate, and lung cancers.

But Setlow cautions that he's talking about only brief exposure. "If you get too much sun exposure for too long, you might get malignant melanoma," says Setlow, who is credited with establishing the link between sunlight and the deadly skin cancer malignant melanoma. "But if you have an internal cancer, you might be cured."

Less important in the debate, he adds, is the risk of getting non-melanoma skin cancers from sun exposure. "Squamous and basal [two other forms of skin cancer] are easy to cure," says Setlow.

Sunlight's Cancer Connection

For the study, the researchers used a special model to calculate how much vitamin D is triggered by sunlight exposure in different populations of people, depending on how far they live from the equator.

Among the findings: those who live in Australia produce 3.4 times as much vitamin D as a result of sun exposure than do people who live in the United Kingdom, and 4.8 times as much as Scandinavians do.

The team also looked at the incidence of various forms of cancer classified by latitude and then determined the survival rates from these cancers.

In populations with similar skin types, the incidence of all kinds of skin cancer increases from north to south, they found.

The incidence of internal cancers -- colon, lung, breast, and prostate -- also increased from north to south. But Setlow's team found that those who lived in southern latitudes -- and who made more vitamin D from sun exposure -- were much less likely to die from those cancers than were the northern latitude residents.

"Vitamin D reduces the death rate from internal cancer," Setlow tells WebMD.

The paper will appear online this week in the Proceedings of the National Academy of Sciences and is scheduled to be published in the Jan. 15 issue.

Sun, Vitamin D, and Cancer

The researchers "took information that was known and looked at it in a different way," says Cedric Garland, DPH, professor of family & preventive medicine at the University of California, San Diego, who has also researched the association between Vitamin D, the sun, and cancer risk.

The new paper, he adds, "draws attention to existing studies that have shown that vitamin D deficiency is a cause of cancers of the breast, colon, prostate, ovary, pancreas, and kidney.''

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