Scientists at U.S. Department of Energy's Brookhaven National Laboratory and colleagues in Norway have found evidence that the increased risk of melanoma cancer from sun exposure is outweighed by reduced risk of internal cancers as a result of increased vitamin D production.
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.
Since melanoma is caused by UVA radiation but vitamin D synthesis is caused by UVB radiation the scientists suggest that sun screens should selectively filter out the UVA in order to give the best of both worlds: no higher melanoma risk combined with lower internal cancer risk.
|Share |||Randall Parker, 2008 January 08 11:26 PM Aging Lifestyle Studies|