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Modest Exercise Lowers Breast Cancer Risk

Less Than 3 Hours a Week Offers Protection Close to Longer Workouts

It's an Estrogen Thing

"Leanness affects estrogen metabolism, and higher levels of estrogen increases breast cancer risk," says Grace Wyshak, PhD, of Harvard's School of Public Health, who has also studied the effects of exercise on breast cancer.

In one 1985 study on nearly 4,000 women, Wyshak noted that women who engaged in regular physical activity during their college years or earlier could decrease their risk of breast cancer by 17%. In a follow-up study done 15 years later, she found that some protective effect lingered, even when their activity levels waned.

Despite past activity levels, it's never too late to reap these cancer-fighting rewards. And staying trim plays an especially important role as women age.

"In middle and older women, reducing body fat will reduce the level of estrogen, because after menopause, the main source of estrogen is body fat," says McTiernan. "However, exercise can affect other hormones, like insulin, that can also promote tumors. Exercise also improves immune function, which can also reduce risk."

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