"Solar radiation is the main cause of skin cancers. However, it also is a main source of vitamin D for humans. Because the optimal status of vitamin D protects against internal cancers and a number of other diseases, a controversy exists: Will increased sun exposure lead to net health benefits or risks?
We calculated the relative yield of vitamin D photosynthesis as a function of latitude with a radiative transfer model and cylinder geometry for the human skin surface. The annual yield of vitamin D is 3.4 and 4.8 times larger below the equator thanin the U.K. and Scandinavia, respectively.
In populations with similar skin types, there are clear latitude gradients of all major forms of skin cancer, indicating a north-south gradient in real sun exposure. Surprisingly, the incidence rates of major internal cancers also increase from north to south. However, the survival prognosis also improves significantly from north to south. Reasons for these findings are discussed in view of the role of vitamin D.
In Norway, melanoma rates increased by a factor of 6 from 1960 to 1990, while the prognosis improved in the same period. After 1990, melanoma rates have remained constant or even decreased in age groups <50 years, whereas the prognosis has not improved further.
These data, together with those for internal cancers and the beneficial effects of an optimal vitamin D status, indicate that increased sun exposure may lead to improved cancer prognosis and, possibly, give more positive than adverse health effects. "
Moan J, Porojnicu AC, Dahlback A, Setlow RB.
Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure. (link to PubMed) Proc Natl Acad Sci U S A. 2008 Jan 15;105(2):668-73.
The home page of Johan Moan's group: Biophysics and PDT Group (radium.no/moan)
Department of radiation biology
Institute for cancer research