A large clinical trial has found that calcium and vitamin D supplements don’t help postmenopausal women lower their risk of breast cancer. Dr. Rowan Chlebowski, study author and a medical oncologist at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Los Angeles said, "The message is that there's benefit from calcium and vitamin D for fracture risk, but taking those supplements won't be doing much for breast cancer risk. You wouldn't expect that you're doing it to improve breast cancer outcome."

Results of the study released online Tuesday, were expected to be published in the Nov. 19 issue of the Journal of the National Cancer Institute. The study conducted on 36,000 post menopausal women as a part of the Women's Health Initiative was to study the effect of supplements on the incidence of hip fractures, with breast cancer and colorectal cancer as secondary issues.

In the study, all the women were between 50-70 years of age and had no history of breast cancer. They were randomly given either 1,000 milligrams of calcium plus 400 international units daily of vitamin D, or a placebo for an average of seven years. They were allowed during this period to take additional calcium and vitamin D supplements.

The researchers found at the end of the seven years that there were 528 cases of breast cancer in the group taking calcium and vitamin D as compared to 546 cases in the placebo group, which is not considered to be statistically significant

"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," said Chlebowski.  "Although further study of relationships among calcium plus vitamin D supplement use and breast cancer can be considered, current evidence does not support their use in any dose to reduce breast cancer risk."

Dr. Jennifer A. Ligibel, a medical oncologist at the Dana-Farber Cancer Institute not involved in the study said, "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."

Dr. Powel Brown, director of the cancer prevention program at the Lester and Sue Smith Breast Center at Baylor College of Medicine in Houston said, "This trial is disappointing in that it does not demonstrate a significant cancer preventive effect from vitamin D and calcium in postmenopausal women.

Brown pointed out that the study didn't look at premenopausal women. "It may be that the benefit of vitamin D in cancer prevention may be restricted to premenopausal women," he said, adding that the study "doesn't diminish the positive effects on bone health from vitamin D and calcium."