Calcium and Vitamin D Supplements Don't Appear to Reduce Risk

R.T. Chlebowski and others

American Society of Clinical Oncology Annual Meeting, June 2006, Abstract LBA6

Is this for me? If you're wondering whether taking certain vitamins can reduce your risk of breast cancer, you might want to read this article.

What question is the study trying to answer? The researchers wanted to know if taking vitamin D and calcium supplements would reduce the risk of breast cancer in post-menopausal women with no history of the disease.

Some small, earlier studies had suggested that vitamin D and calcium supplements may offer protection from breast cancer. But this idea had never been studied in a randomized trial (a trial that assigns people to different treatment groups entirely by chance).

Study design: More than 36,000 post-menopausal women with no history of breast cancer were randomly assigned to take, every day, either:

• 1,000 milligrams of calcium carbonate and 400 IU (international units) of vitamin D (18,176 women), or
• placebo pills ("dummy" pills that looked exactly like the supplements) (18,106 women).

The women were followed for about seven years.

The researchers looked at how many women developed breast cancer, the size of the cancers that developed, and whether or not women had taken vitamin D or calcium supplements before they began this study.

This study is part of the Women's Health Initiative (WHI), funded by the National Institutes of Health. The WHI is a long-term health study that focuses on strategies for preventing heart disease, breast and colorectal cancer, and fracture in post-menopausal women.

Study results: After seven years, taking vitamin D and calcium supplements didn't appear to reduce the risk of breast cancer in post-menopausal women who had never had the disease. In both groups — the women who took supplements and the women who didn't — about 3 percent developed breast cancer.

The cancers were smaller in the women who took the supplements, but this difference was not statistically significant, which means that it could be due just to chance.

Among women who didn't take any vitamin D or calcium supplements before the study, those in the study group who took the supplements appeared to have about an 18% reduction in breast cancer risk compared to those who took the placebos. But this difference also wasn't statistically significant.

Take-home message: This study didn't show a connection between reduced breast cancer risk and taking vitamin D and calcium supplements. But it's difficult to pinpoint specific foods or vitamins that are linked to reducing breast cancer risk. Your overall diet — how much saturated and trans fat it contains, as well as fiber and other healthy nutrients — plays a larger role in risk reduction than any one dietary component. Other factors, such as how much exercise you get, your weight, and whether or not you smoke, also affect your risk of breast cancer.

The results of this study are also difficult to interpret because the researchers didn't tell the women to stop taking any supplements they may have already been using. So a woman taking the placebos may have been taking other vitamin D or calcium supplements.

No food or diet can prevent you from getting breast cancer. But some foods can make your body the healthiest it can be, boost your immune system, and help keep your risk for breast cancer as low as possible. Current research findings suggest that physical activity, a healthy diet, and a healthy weight can help reduce the risk of getting breast cancer for the first time.

For more information on changes you can make in your lifestyle and environment to reduce your risk of breast cancer, visit our Lower Your Risk section. And stay tuned to breastcancer.org for the latest information on nutrition and breast cancer.

Read more about the topics discussed in this Research News article:

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