Vitamin D, Calcium Not Linked to Lower Breast Cancer Risk

THURSDAY, Nov. 13 (HealthDay News) -- Calcium and vitamin D supplementation does not reduce the risk of breast cancer in postmenopausal women, according to the results of a study published in the Nov. 19 issue of the Journal of the National Cancer Institute.

Rowan T. Chlebowski, M.D., Ph.D., of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, Calif., and colleagues conducted a randomized, double-blind, placebo-controlled trial of 36,282 postmenopausal women enrolled in the Women's Health Initiative trial. Participants were randomized to receive either calcium plus vitamin D supplements or placebo. A nested case-control study was used to assess serum levels of 25-hydroxyvitamin D, a vitamin D metabolite.

After a mean of seven years, the incidence of invasive breast cancer was similar in the supplement and placebo groups (528 versus 546, respectively). This was true for cases of in situ breast cancer, as well (145 cases in the supplement group versus 152 cases in the placebo group), the researchers report. Supplement use had no effect on the risk of invasive breast cancer, regardless of baseline characteristics. Also, no significant association was noted between levels of 25-hydroxyvitamin D and risk of breast cancer, after adjusting for body mass index and physical activity.

The authors conclude that these results "do not support a causal relationship between calcium and vitamin D supplement use and reduced breast cancer incidence, despite the association observed in some epidemiological studies."

Chlebowski reports financial relationships with the pharmaceutical industry.

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