More sun exposure boosts vitamin D, could outweigh skin cancer risks in certain populations

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Public release date: 7-Jan-2008

http://www.eurekalert.org/pub_releases/2008-01/dnl-mse010408.php

Contact: McNulty Walsh

kmcnulty@...

DOE/Brookhaven National Laboratory

More sun exposure may be good for some people

Study finds boost in vitamin D could outweigh skin cancer risks in

certain populations

UPTON, NY - A new study by scientists at the U.S. Department of Energy's

Brookhaven National Laboratory and colleagues in Norway suggests that

the benefits of moderately increased exposure to sunlight - namely the

production of vitamin D, which protects against the lethal effects of

many forms of cancer and other diseases - may outweigh the risk of

developing skin cancer in populations deficient in vitamin D. The study

will be published online in the Proceedings of the National Academy of

Sciences the week of January 7, 2008.

" We know that solar radiation is the leading cause of skin cancer, " said

communicating author Setlow, a Senior Biophysicist Emeritus at

Brookhaven and a well-known expert on the link between solar radiation

and skin cancer. Setlow's group was the first to establish that

ultraviolet A (UVA) radiation and visible light are the primary causes

of malignant melanoma, the deadliest form of skin cancer. He and his

colleagues emphasize that people need to protect themselves from the

harmful effects of sun exposure.

But solar radiation is also a major, if not the main, source of vitamin

D in humans. In the presence of sunlight, the body converts certain

precursor chemicals to active vitamin D.

" Since vitamin D has been shown to play a protective role in a number of

internal cancers and possibly a range of other diseases, it is important

to study the relative risks to determine whether advice to avoid sun

exposure may be causing more harm than good in some populations. " The

concern, he says, is particularly great in populations from northern

latitudes, such as Scandinavia, where sun exposure is extremely limited.

In the current study, Setlow and his colleagues used a model

incorporating information on solar radiation intensity and a vertical

cylinder shape to represent the human body's skin surface to calculate

the relative production of vitamin D via sunlight as a function of

latitude, or distance from the equator. The cylindrical model more

realistically represents human body sun exposure than flat surface

exposure measurements used in previous models. The scientists also

examined the incidence of and survival rates for various forms of cancer

by latitude.

According to the calculations, people residing in Australia (just below

the equator) produce 3.4 times more vitamin D as a result of sun

exposure than people in the United Kingdom, and 4.8 times more than

people in Scandinavia.

" There is a clear north-south gradient in vitamin D production, " Setlow

says, " with people in the northern latitudes producing significantly

less than people nearer the equator. "

In populations with similar skin types, there is also a clear increase

in the incidence of all forms of skin cancer from north to south. " This

gradient in skin cancer rates indicates that there is a true north-south

gradient in real sun exposure, " Setlow says.

The scientists also found that the incidence rates of major internal

cancers such as colon cancer, lung cancer, and cancers of the breast and

prostate also increased from north to south. However, when the

scientists examined the survival rates for these cancers, they found

that people from the southern latitudes were significantly less likely

to die from these internal cancers than people in the north.

" In previous work, we have shown that survival rates for these cancers

improve when the diagnosis coincides with the season of maximum sun

exposure, indicating a positive role for sun-induced vitamin D in

prognosis - or at least that a good vitamin-D status is advantageous

when combined with standard cancer therapies, " Setlow says. " The current

data provide a further indication of the beneficial role of sun-induced

vitamin D for cancer prognosis. "

So, how can people get the benefits of vitamin D without running the

risk of deadly skin cancer "

" As far as skin cancer goes, we need to be most worried about melanoma,

a serious disease with significant mortality, " Setlow says.

Melanoma is triggered by UVA (the long UV wavelengths) and visible

light. Vitamin-D production in the body, on the other hand, is triggered

by UVB (the short UV wavelengths at the earth's surface). " So perhaps we

should redesign sunscreens so they don't screen out as much UVB while

still protecting us from the melanoma-inducing UVA and visible light, "

Setlow says.

Increased UVB exposure may result in an increase in non-melanoma skin

cancers. But these are relatively easy to cure and have very low

mortality rates compared with the internal cancers vitamin D appears to

protect against, Setlow adds.

Another option would be to increase vitamin D consumption while

continuing to wear sunscreen. Vitamin D is easily accessible in many

foods and liquids, such as cod liver oil and milk, and in dietary

supplements.

###

In addition to Setlow, the research team includes Johan Moan and Alina

Carmen Porojnicu of the Institute for Cancer Research in Oslo, Norway,

and Arne Dahlback of the University of Oslo. Moan also holds an

appointment at the University of Oslo. The research was funded by Sigval

Bergesen D.Y. og hustru Nankis Foundation, by The Research Foundation of

The Norwegian Radiumhospital and by Helse-Sør Norway. Setlow's

laboratory and facilities at Brookhaven Lab are supported by the Office

of Biological and Environmental Research within the U.S. Department of

Energy's Office of Science.

--

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