Calcium and Vitamin D – and Breast Cancer

In 1993 and 1995 a total of over 30,000 women over 45 years of age participated in The Women's Health Study, a large-scale, long term study involving thousands of women across the United States. The participants provided medical history, lifestyle factors (such as smoking or exercise), and answered a detailed dietary questionnaire (Arch Intern Med 2007;167(10):1050-1059). Participants reported on over 100 different foods, beverages, and supplement items such as calcium and vitamin D and estimated their average intake over the previous 12 months.

Over 10,000 premenopausal women and over 20,000 postmenopausal women were then recontacted yearly for ten years in order to fill out followup questionnaires. These included questions about whether the participants had been diagnosed with breast cancer. If they had been diagnosed, the researchers performing the study sought permission to analyze their medical records pertaining to their cancer.

For those women who had been diagnosed with breast cancer, the scientists looked closely at their intake of calcium and vitamin D from all sources, including dairy products, supplements, and other sources. They then related that information to the types of breast cancer each woman had as well as other, more common risk factors for breast cancer.

They found that those premenopausal women who consumed more total calcium and vitamin D had a lower risk of breast cancer, with the greatest effects seen on the risk of the more aggressive types of breast cancers.

On the other hand, calcium and vitamin D did not appear to have any effect on postmenopausal women's risk. The researchers note, however, that it's common for postmenopausal women to not be getting enough calcium and vitamin D in their diets.

What this means for you

While more research is needed, your take-home message is a reminder that most women aren't getting enough calcium in their diets. (Vitamin D is often packaged with calcium because it helps the calcium be absorbed more readily into the body.)

First posted: June 6, 2007