High intake of vitamin D and calcium appears to reduce the risk of breast cancer in pre-menopausal women, but not in postmenopausal women, according to a study by researchers at Brigham and Women's Hospital and Harvard Medical School, Boston.

Early animal and lab studies show that calcium and vitamin D provides a preventative effect against breast cancer, according to background information in the study report.   But epidemiologic studies have not been consistent.

For the study, Jennifer Lin, Ph.D., and colleagues followed 10,578 pre-menopausal and 20,909 postmenopausal women age 45 and older who were enrolled in the Women's Health Study.

Participants were surveyed for their medical history, lifestyle as well as dietary habits including the types of foods, beverages and supplements they used during the previous years. In the first year, subjects returned questionnaires every six months and thereafter, they answered questionnaires every year.

During the average 10-year follow-up, breast cancer was diagnosed in 276 pre-menopausal women and 743 postmenopausal women.

The study published in the May 28 issue of Archives of Internal Medicine found that there was a moderate inverse correlation between intake of calcium and vitamin D intake and risk of breast cancer in pre-menopausal women.

Specifically, those with their intake of calcium and vitamin D in the highest quintile were 39 percent less likely to develop breast cancer compared to those with their intake in the lowest quintile.

When vitamin D was considered along, the risk reduction in those with the highest intake was 35 percent compared to those with the lowest intake.

The association was even more significant for more aggressive breast tumors, according to the researchers.

However, the apparent preventative effect was not found in postmenopausal women.

"A possible explanation for the evident difference by menopause status may be related to the joint relationship among calcium, vitamin D and insulinlike growth factors (IGFs)," they continue.

"In vitro studies have suggested that calcium and vitamin D exert anticarcinogenic effects on breast cancer cells expressing high levels of IGF-1 and IGF binding protein 3. Calcium, vitamin D and IGF binding protein 3 have been shown in vitro to interact with each other in promoting growth inhibition in breast cancer cells."

The reason why postmenopausal women did not receive the apparent preventive effect is because blood levels of these compounds decline with age, the researchers say.

Calcium and vitamin D, particularly the latter, have been found to have a wide range of preventative effects against cancer among others.   The current recommended daily allowance for vitamin D is too low, some vitamin D experts have suggested.

Source:

Intakes of Calcium and Vitamin D and Breast Cancer Risk in Women
Jennifer Lin; JoAnn E. Manson; I-Min Lee; Nancy R. Cook; Julie E. Buring; Shumin M. Zhang
Arch Intern Med. 2007;167:1050-1059.