No breast cancer benefit from vitamins

Women who took calcium and vitamin D supplements developed breast cancer at the same rate as women who didn't take them, a large clinical trial has found, contradicting conclusions from previous studies that hinted at benefits from vitamin D.

The study - part of the massive Women's Health Initiative - followed more than 36,000 post-menopausal women who were randomly assigned to take calcium and vitamin D supplements or a placebo. The researchers were mainly interested to see whether the supplements would make a difference in their incidence of hip fracture, but breast cancer was a secondary outcome they studied.

After about seven years, there were 528 cases of breast cancer in the group taking calcium and vitamin D compared with 546 cases in the placebo group - a difference not considered 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," the authors, led by Dr. Rowan T. Chlebowski of the University of California, Los Angeles, wrote in the Journal of the National Cancer Institute. "Current evidence does not support their use in any dose to reduce breast cancer risk."

The study is the first rigorous test of vitamin D that accounts for factors the earlier, observational studies were unable to capture, said Dr. Jennifer A. Ligibel, a medical oncologist at the Dana-Farber Cancer Institute in Boston. Women who take dietary supplements might be healthier than women who don't, for example, and that could have biased the previous studies. But there are still questions about vitamin D, she said.

"I think this is an important study. It tells us there is absolutely more work that needs to be done on vitamin D," Ligibel, who was not involved in the study, said in an interview. "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 appearing in the journal, Dr. Corey Speers and Dr. Powel Brown of Baylor College of Medicine suggest further work to see 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.

ELIZABETH COONEY

Correction: Because of a reporting error, a story on Wednesday's Nation page about calcium and vitamin D supplements and breast cancer misidentified where Dr. Rowan T. Chlebowski works. He is a researcher at the Los Angeles Biomedical Research Institute.