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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, overturning 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 to see whether the supplements would make a difference in their incidence of hip fracture. Breast cancer and colorectal cancer were secondary outcomes studied by the researchers.

After about seven years, there were 528 cases of breast cancer in the group of women taking calcium and vitamin D compared with 546 cases in the placebo group — a difference not considered statistically significant. Blood tests for vitamin D levels also showed no correlation with breast cancer rates. Women who were already taking the supplements — about the same number in the supplement group and the placebo group — had been allowed to continue doing so.

“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 Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, write in the online version of the Journal of the National Cancer Institute. “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.”

The study is valuable because it 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. Women who take dietary supplements might be healthier than women who don’t, for example. But there are still questions about vitamin D that need to be answered.

“I think this is an important study. It tells us there is absolutely more work that needs to be done on vitamin D,” Ligibel said in an interview. She was not involved in the study. “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 of the National Cancer Institute, Dr. Corey Speers and Dr. Powel Brown of Baylor College of Medicine praise the study’s design and execution, but 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 the hormone therapy also being studied might have confounded the results.

“The potential health benefits of vitamin D and calcium may yet still have a bright future,” they write.

Few types of food or their components, from fat to carbohydrates to fruits and vegetables, have turned out to have a proven relationship in the development of breast cancer or its recurrence, with the exception of alcohol, which has been linked to increased risk, said Ligibel of Dana-Farber. She tells her patients about preliminary evidence that a diet high in fat might not be the best.

“I think there is a lot to learn in this area still, but I personally do not counsel my patients that they need to make tremendous dietary changes based on the information available,” she said.
Source: http://www.boston.com/news/health/blog/2008/11/calcium_plus_vi.html

Tags: Breast Cancer, calcium, Cancer, vit D

This entry was posted on Friday, December 5th, 2008 at 4:34 pm and is filed under Breast Cancer, Cancer, Women. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.