Increased exposure to sunlight - which increases levels of vitamin D in the body - may decrease the risk of advanced breast cancer, say scientists from the University of Southern California and Wake Forest University School of Medicine. In a study in the American Journal of Epidemiology, the researchers found that women with high sun exposure had half the risk of developing advanced breast cancer, which is cancer that has spread beyond the breast. These findings were observed only for women with naturally light skin color. The study defined high sun exposure as having dark skin on the forehead, an area that is usually exposed to sunlight.
In women with naturally light skin pigmentation, the group without breast cancer had significantly more sun exposure than the group with breast cancer. The fact that this difference occurred only in one group suggests that the effect was due to differences in vitamin D production - and wasn't just because the women were sick and unable to go outdoors. In addition, the effect held true regardless of whether the cancer was diagnosed in the summer or in the winter. The difference was seen only in women with advanced disease, suggesting that vitamin D may be important in slowing 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," said lead researcher Esther John. "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."
The study noted that sunlight is not the only source of vitamin D, which can be obtained from multivitamins, fatty fish and fortified foods such as milk, certain cereals and fruit juices. "If future studies continue to show reductions in breast cancer risk associated with sun exposure, increasing vitamin D intake from diet and supplements may be the safest solution to achieve adequate levels of vitamin D," concluded co-researcher Gary Schwartz.
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Source: Wake Forest University Baptist Medical Center
