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Study Links Dairy Products to Moderate Breast Cancer Risk Reduction

Armen Hareyan's picture

Breast Cancer and Dairy Products

A new American Cancer Society study finds low fat dairy products may reduce the risk of postmenopausal breast cancer, supporting the hypothesis that dietary calcium and/or some other components in dairy products may reduce the risk of the disease. The study found women who consumed two or more servings of dairy products per day had up to 20 percent lower risk of postmenopausal breast cancer compared to women with the lowest consumption of dairy products. The association was slightly stronger among women with estrogen-receptor positive tumors, the most common type.

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Dairy products have been hypothesized to have paradoxical effects on breast cancer risk because they contain both potentially protective compounds, like calcium and vitamin D, and compounds that may increase the risk of cancer, such as hormones and insulin-like growth factor I (IGF-I). Studies to date have had inconsistent findings.

For the current study, researchers led by Marji McCullough, ScD, RD, senior epidemiologist in the American Cancer Society's Epidemiology & Surveillance Research department, reviewed dietary questionnaires filled out by more than 68,000 postmenopausal women participating in the Society's Cancer Prevention Study II (CPS-II). They found women who ate the most calcium-rich foods (e.g. low fat milk, cheese, and yogurt) were 20 percent less likely to be diagnosed with breast cancer than those reporting the lowest intake. However, neither use of calcium supplements nor vitamin D intake lowered the risk.

"Our findings suggests that dairy products, composed mainly of low-fat sources, or some component within these foods are associated with a small but significantly lower risk of breast cancer in postmenopausal women," said McCullough. "Work is still needed to more clearly identify what may be the responsible factors. And while we controlled to the best of our ability for other possible explanations, it's certainly possible women who consume low-fat dairy products have other health-related behaviors that could also lower the risk."

McCullough says women should be careful how they interpret the study. "It is important to keep in mind that some dairy products, like whole milk and many types of cheese have a lot of saturated fat, which we know can increase the risk of heart disease and possibly other cancers. Also, many dairy products have growth factors such as insulin-like growth factor I, which have been shown to promote breast cancer cell growth. More study is needed before we can make concrete recommendations."