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Study finds lifelong exercise may halve risk of breast cancer

Women benefit by working out 5 hours a week

WASHINGTON -- Exercising for five or more hours a week throughout life can cut a woman's risk of breast cancer by more than half, researchers said.

Strenuous or moderate exercise from the teens to about age 50 reduces the risk of some types of breast cancer by as much as 55 percent, according to a study published in yesterday's issue of the Archives of Internal Medicine. Previous studies asked women about current exercise habits and not activities over time.

"It's long-term activity that matters," Leslie Bernstein, one of the study's authors, said in an interview. "This may explain why asking women what they currently do does not adequately capture physical activity relevant to breast cancer risk. It is really activity during reproductive years and into the early 50s in our study, which predicts breast cancer risk."

Breast cancer is the most common non skin cancer in the nation .

Women who exercised strenuously over a long period of time were 55 percent less likely to get the most invasive breast cancer, and women who exercised moderately had a 47 percent lower risk than those who exercised for less than 30 minutes a week, the study said. Other types of breast cancer weren't affected by strenuous or moderate exercise.

Physical activity can shorten menstrual cycles and reduce the frequency of ovulation. That limits the time women are exposed to ovarian hormones, which are linked to breast cancer, said Bernstein, professor of preventive medicine at the University of Southern California, Los Angeles.

Women who exercise regularly are also less likely to be overweight, a condition that contributes to breast cancer risk .

More than 40,000 women will die from breast cancer this year, according to the National Cancer Institute website. The cancer can also affect men.

Researchers collected data on 110,599 women ages 20 to 79, who were asked about the intensity and duration of their physical activity from high school to their current age. More studies are needed, the authors said.