Vitamin D, Calcium: A Sun-sational Combo

Vitamin D and calcium are best known for their bone-strengthening properties, but a new study suggests that the vitamin-mineral combination also may reduce the risk of breast cancer.

“Adequate intakes of calcium and vitamin D are necessary for women in keeping up their health,” says Jennifer Lin, lead author of the study published in the May issue of Archives of Internal Medicine. “Additionally, these two nutrients may help prevent breast cancer development, especially among pre-menopausal women.”

Harvard Medical School researchers focused on data from more than 10,500 pre-menopausal women and almost 21,000 postmenopausal women enrolled in the Women’s Health Study, a clinical trial that began in September 1991 and will run through August 2009.

The data included information on what the women ate and the dietary supplements they took while noting how many participants developed breast cancer over an average of 10 years (276 pre-menopausal participants and 743 postmenopausal participants).

Researchers found that pre-menopausal participants who maintained high levels of vitamin D and calcium had a 30-percent lower risk of developing breast cancer—cutting their overall chances of being diagnosed with breast cancer by almost a third. This association was not found for postmenopausal women, however.

“Calcium and vitamin D may confer protection against breast tumorigenesis,” Lin says, noting that various animal studies have also seen a connection between calcium/vitamin D intake and breast cancer prevention. “However, more studies are necessary to investigate the potential utility of these two nutrients in breast cancer development.”

Other experts, like epidemiologist Victoria Stevens at the American Cancer Society, agree that further studies are needed and stress the fact that the exact effect of calcium and vitamin D on breast cancer is still not clear.

"I really don't think that one can say from this study that the effect is only in pre-menopausal women, because there are a number of factors in the study that may have limited the ability to see the effect," Stevens says. "This is particularly true for vitamin D, because most vitamin D comes from exposure to sunlight, which they did not take into account."

Vitamin D is produced naturally by the body following exposure to sunlight and also can be ingested through fortified products like milk, soy milk and cereal grains. It also helps the body to absorb calcium, which is a mineral component of human bones and teeth.