Vitamin D Likely Responsible for Decreased Risk of Advanced Breast Cancer in Women with Greater Sun Exposure

An article published online on October 12, 2007 the American Journal of Epidemiology revealed the finding of researchers from the Northern California Cancer Center, the University of Southern California, and Wake Forest University School of Medicine that increased levels of vitamin D in the body which are found among those with greater sunlight exposure are associated with a reduced risk of developing advanced breast cancer , defined as disease that has spread beyond the breast.

Esther John, PhD of Northern California Cancer Center and colleagues matched 1,788 Hispanic, African-American, and non-Hispanic White women with newly diagnosed breast cancer with 2,129 control subjects. To calculate sun exposure, the color of underarm skin, which is not usually directly exposed to sunlight, was classified as light, medium, or dark, and compared with the color of the forehead, which is normally exposed to the sun.

The team determined that light skinned women with the most exposure to the sun had half of the risk of developing advanced breast cancer than those whose exposure was low. Because the finding occurred in only one group of women, the researchers suggest that the effect was due to differences in vitamin D production. The effect was seen only in advanced and not localized breast cancer, which may mean that vitamin D slows the growth of breast cancer cells.

“We believe that sunlight helps to reduce women’s risk of breast cancer because the body manufactures the active form of vitamin D from exposure to sunlight,”
 Dr John stated. “It is possible that these effects were observed only among light- skinned women because sun exposure produces less vitamin D among women with naturally darker pigmentation.”

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