Sunlight may cut breast cancer risk for some women

By Anthony J. Brown, MD

NEW YORK (Reuters Health) - Exposure to sunlight may reduce the risk of advanced breast cancer in women with light skin pigmentation, according to the results of a population-based study appearing in the American Journal of Epidemiology.

"We believe that sunlight helps reduce women's risk of breast cancer because the body manufactures the active form of vitamin D from exposure to sunlight," lead author Dr. Esther M. John, from the Northern California Cancer Center in Fremont, said in a statement.

"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 is not the first to link sun exposure with a reduced risk of breast cancer, but the way that sun exposure was measured was new, according to John.

"We measured women's skin pigmentation on the forehead (usually exposed to the sun) and on the upper inner arm (usually not exposed to the sun) and used the difference between the two measurements as a measure of past sun exposure. Other studies have usually relied on self-reported sun exposure," she told Reuters Health.

The study included 1788 women with breast cancer and a comparison group of 2129 "controls" - women without breast cancer, living the San Francisco Bay Area of California (1995-2003). In addition to the sun exposure test mentioned, skin specimens were obtained and analyzed in a subgroup of subjects in each group.

High levels of sun exposure were associated with a 47-percent reduced risk of advanced breast cancer in light-skinned women, the results show. Mutations of the vitamin D receptor gene did not affect the association.

However, this association was not seen in women with medium or dark skin and was only apparent for advanced disease, not localized breast cancer.