Sunlight: Good for Bad for Cancer Risk?

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.''

Advice on Sun and Vitamin D

Getting brief, unprotected sun exposure might be wise, especially for those
over age 60, Setlow says, who are more likely than younger people to be vitamin
D-deficient. The chance of brief sun exposure causing deadly skin cancer, which
generally takes years to develop, is less likely at that age, he says.

Garland's recommendation: Increase your intake of vitamin D, especially if
you think you might be deficient.  He recommends 1,000 to 2,000
international units (IU) a day plus 10 or 15 minutes of exposure to the sun
within an hour of noon on clear days, with 40% of your skin exposed. Getting a
doctor's approval first is wise.

Those two strategies, he says, "will bring the blood level of vitamin D
up to what is considered protective."

Skin Cancer Foundation Disagrees

Exposure to unprotected sun is not a good idea, according to the Skin Cancer
Foundation.

"While some population studies suggest that vitamin D levels, such as
those that could result from sun exposure, may be beneficial for cancer
survival, current scientific data suggest that proper sun protection remains a
key element of a skin cancer protection program," says David J.
Leffell, MD, vice president of the Skin Cancer Foundation and director of the
Yale Medical Group in New Haven, Conn.

Until more is known, he says, dermatologists recommend using sunscreen and
other sun precautions and getting vitamin D from foods and supplements.

The adequate intake of vitamin D as set by the Institute of Medicine is 200
IUs for those aged 19 to 50, 400 IUs for those 51 to 70, and 600 IUs for those
over age 71. The safe upper limit is 2,000 IUs for those over age 19. Sources
of vitamin D from food include salmon, mackerel, and vitamin D-fortified milk
and cereal.

By Kathleen Doheny
Reviewed by Louise Chang
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