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Feb. 1, 2005 -- New studies show a cancer paradox: Sun exposure -- a known cause of skin cancer -- has an anticancer effect.

How this happens is not quite clear. But two new studies in the Feb. 2 issue of the Journal of the National Cancer Institute show that these night-and-day effects of sunshine aren't moonshine.

A large study of the fair-skinned denizens of Sweden and Denmark shows that those with the most sunburns, the most beach vacations, and/or the most sunbathing -- five to 10 years ago and at age 20 -- were least likely to get malignant white blood cell cancers.

And U.S. researchers report the surprising finding that people who get the most deadly kind of skin cancer -- melanoma -- are less likely to die of the disease if, in the past, they'd spent a lot of time in the sun.

The unenviable task of making sense of all this falls to melanoma expert Kathleen M. Egan, ScD, associate professor of medicine at Vanderbilt Ingram Cancer Center in Nashville, Tenn., and colleagues. Their JNCI editorial accompanies the two studies.

"Sunlight, we know, is an established human carcinogen," Egan tells WebMD. "These two investigations ... report findings that sunlight is associated with a beneficial influence on cancer. That flies in the face of what we know about sunlight in terms of carcinogenic influence -- but it is, in fact, in line with earlier descriptive data of a preventive effect on prostate cancer, colon cancer, and even breast cancer."

The earlier studies to which Egan refers show that U.S. cancer death rates go up the farther north a person lives.

The new studies, she says, are the first to show that these peculiar reports really are linked to sun exposure and not to racial or economic differences.

"No one is suggesting that anyone strip off whatever garments they might take off to get themselves dosed with sunlight," Egan says. "The important message is that that this anticancer effect is very unlikely to be sunlight itself. It is more likely to be vitamin D generated by sun exposure. We all need to stay tuned and let the research community go to work and try to tease out whether this is really a vitamin D effect."