A U.S. research team has found that increased exposure to sunlight -- which increases levels of vitamin D in the body -- may decrease the risk of advanced breast cancer, according to a study reported Friday in the latest issue of American Journal of Epidemiology. (File Photo)

    WASHINGTON, Oct. 19 (Xinhua) -- A U.S. research team has found that increased exposure to sunlight -- which increases levels of vitamin D in the body -- may decrease the risk of advanced breast cancer, according to a study reported Friday in the latest issue of American Journal of Epidemiology.

    The researchers from the Northern California Cancer Center, the University of Southern California, and Wake Forest University 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, compared to women with low sun exposure. These findings were observed only for women with naturally light skin color.

    The fact that this difference occurred only in light skin color group suggests that the effect was due to differences in vitamin Dproduction, said the researchers. And 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 Esther John, lead researcher on the study from the Northern California Cancer Center. "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."

    Skin color is an important factor that determines how much vitamin D is produced in the body after sun exposure. Dark-skinned individuals produce up to 10 times less vitamin D than light-skinned individuals for the same amount of time spent in the sun.

    These new findings are consistent with previous research by John and colleagues that had shown that women who reported frequent sun exposure had a lower risk of developing breast cancer than women with infrequent sun exposure.

    The researchers stressed 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. Women should not try to reduce their risk of breast cancer by sunbathing because of the risks of sun-induced skin cancer, they said.

    "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," said Gary Schwartz, a co-researcher from Wake Forest University.