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Breast Cancer Health Center

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Exercise Lowers Breast Cancer Risk

Moderate Activity Level Cuts Risk of Aggressive Cancer Type by a Third in Older Women
WebMD Health News
Reviewed by Louise Chang, MD

Dec. 11, 2006 -- Regular exercise helps protect older women against breast cancer -- in particular, a less common but hard-to-treat form of the disease, a new study shows.

In a study that looked at the link between exercise and breastcancer in more than 36,000 women, researchers found a 34% reduction in the likelihood of getting one specific type of breast cancer in women with high levels of physical activity.

The researchers from the Mayo Clinic in Rochester, Minn., conclude that postmenopausal women can lower their risk of developing breast cancer by engaging in moderate exercise.

The strongest evidence of a benefit was in preventing an aggressive, hormone-driven cancer known by doctors as estrogen-receptor positive and progesterone-receptor negative (ER+/PR-).

Women with a high level of physical activity were a third less likely to develop that type of cancer than women in a low activity group.

That high level of exercise also resulted in a 14% reduction in breast cancer risk overall, compared with women with low physical activity. However, after adjusting for body mass index (BMI) in the women, the risk reduction dropped to 9% -- a number not considered significant in this study.

BMI is used to help determine obesity status. Obesity has been identified as a strong independent risk factor for breast cancer.

The findings are reported in the latest issue of Archives of Internal Medicine.

"This study provides additional evidence that physical activity helps protect against breast cancer," researcher James R. Cerhan, MD, PhD, tells WebMD. "And it appears that it is never too late to begin an exercise program, even if you haven't been physically active in the past."

The Importance of Tumor Type

The new study is not the first to find exercise beneficial for lowering breast cancer risk. But it is the first large investigation to quantify this benefit by tumor type.

Cerhan and colleagues used data from a large, ongoing health trial of postmenopausal women, known as the Iowa Women's Health Study, in their effort to understand the impact of exercise on different types of breast cancer.

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