Study Finds No Breast Cancer Reduction From Calcium, Vitamin D Supplements

Main Category: Breast Cancer
Also Included In: Nutrition / Diet;  Clinical Trials / Drug Trials
Article Date: 14 Nov 2008 - 8:00 PDT

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Women who took vitamin D and calcium supplements developed breast cancer at the same rate as those who did not take the supplements, according to a study by the Women's Health Initiative that is published in the Journal of the National Cancer Institute, the Boston Globe reports. According to the Globe, the findings "contradic[t] conclusions from previous studies that hinted at benefits from vitamin D." The authors -- led by Rowan Chlebowski of the University of California-Los Angeles -- wrote, "The main findings 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," adding, "Current evidence does not support their use in any dose to reduce breast cancer risk" (Cooney, Boston Globe, 11/12).

For the study, the researchers tracked 36,282 postmenopausal women for an average of seven years. Each participant received a combined pill of 1,000 milligrams of calcium and 400 international units of vitamin D. Over the course of the study, 528 of the 18,176 women -- or 2.9% -- who received the combined pill developed invasive breast cancer, compared with 546 of the 18,106 women -- or 3% -- who received a placebo (Kaplan, Los Angeles Times, 11/12). According to the Globe, the difference between the groups is not considered statistically significant.

Jennifer Ligibel, a medical oncologist at the Dana-Farber Cancer Institute who was not involved in the study, said that the new research is the first rigorous test of vitamin D supplementation that accounts for factors that were not captured in earlier, observational studies. For example, she said that women who take dietary supplements might be healthier to begin with than those who do not, which could have influenced the previous studies. Ligibel added, "I think this is an important study. It tells us there is absolutely more work that needs to be done on vitamin D. I do think the study should put a little bit of brakes on people telling people to take huge doses of vitamin D to prevent cancer."

In an editorial also published in the journal, Corey Speers and Powel Brown of Baylor College of Medicine wrote that further research should be done to determine whether the age of the women, the dose of vitamin D they were taking, the calcium they took with it and hormone therapy might have confounded the results (Boston Globe, 11/12).

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