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Getting a little more sun, vitamin D may reduce overall cancer risk.

Increased exposure to solar radiation--an optimal source of vitamin D--may lead to improved cancer prognosis and may contribute more positive health effects, researchers in Norway contend.

"So far, epidemiologic data for cancer argue for an overall positive role of sun-induced vitamin D," wrote the researchers, who were led by Johan Moan, Ph.D., of the department of radiation biology at the Institute for Cancer Research, Oslo, "There may be more beneficial than adverse effects of moderately increased sun exposure, even for total cancer mortality. This message should be addressed to populations at risk for vitamin D deficiency. Trends need to be closely monitored in the future."

Writing in the Proceedings of the National Academy of Sciences (2008;105:668-73), the researchers calculated the relative yield of vitamin D photosynthesis as a function of latitude with radiative transfer model and cylinder geometry for the human skin surface. At the same time, they gathered the age-adjusted cancer incidence and death rates from Australia, New Zealand, Sweden, Norway, Denmark, and the United Kingdom.

The researchers determined that the annual yield of vitamin D is 3.4 times larger below the equator than in the United Kingdom, and 4.8 times larger below the equator than in Scandinavia. "A crucial and as-yet-unanswered question is: Are there north-south gradients in sun exposure habits and in vitamin D intake?" the researchers asked.

When Dr. Moan and his associates looked at international data, they found "no significant gradient" in vitamin D status. This was surprising to them, because the incidence rates of the three major forms of skin cancer have been found to increase from Norway to Australia. Given that "the action spectrum of pre vitamin D photosynthesis and that of squamous cell carcinoma are similar, one should expect to find a vitamin D gradient," they wrote.

The answer "may be found either in the pattern of sun exposure or in differences in vitamin D intake," they continued. But the most likely explanation is that serum measurements of vitamin D "are not standardized well enough for international or interlaboratorial comparisons."

Dr, Moan and his associates also observed that the incidence of major internal cancers increased from north to south. However, survival prognosis improved significantly from north to south latitude. "This finding indicates improved prognosis with decreasing latitude (i.e., with increasing UV exposure)," the researchers wrote. "We find it unlikely that cancer treatment is better in Australia than in the U.K."

The researchers concluded by noting that "in view of the supposedly long latency times for cancer manifestation, decades are needed for final evaluation of the impacts of the anti-sun campaigns with respect to melanoma incidence, cancer prognosis, and other possible positive or adverse health effects."

The study was funded by Sigval Bergesen D.Y. og hustru Nankis Foundation, The Research Foundation of the Norwegian Radiumhospital, and Helse-Sor Norway. The authors reported no conflicts of interest.


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Title Annotation:Clinical Rounds
Author:Brunk, Doug
Publication:OB GYN News
Date:Mar 15, 2008
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