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Exercise May Reduce Breast Cancer

October 25, 1999

CHICAGO (AP) _ Women who exercise an hour a day or more may reduce their risk of breast cancer by 20 percent, according to one of the biggest studies ever done on the topic.

The findings, published in Monday’s Archives of Internal Medicine, add to the growing evidence that exercise can help prevent breast cancer.

A smaller 1997 study in Norway found that women who exercised at least four hours a week were about a third less likely to get breast cancer.

``All the evidence suggests that there’s nothing to lose by women being physically active,″ said Beverly Rockhill, lead author of the most recent study and a researcher at Brigham and Women’s Hospital in Boston.

Researchers believe exercise may affect breast cancer because it lowers the level of estrogen circulating in a woman’s body. Estrogen has been found to stimulate breast cell growth, increasing the chances of cancer, Rockhill said.

The latest study was based on the analysis of questionnaires from 121,701 women nationwide who participated in the Nurses’ Health Study, a long-term health survey of women ages 30 to 55. Rockhill and her colleagues looked at data from 1980 to 1994. They found 3,137 cases of breast cancer among the 85,364 women who answered questions about physical activity.

Of those, 20 percent fewer women who exercised an average of once a day or more got breast cancer, compared with those who exercised less than an hour a week. The exercise included brisk walking and jogging but not things like housework or gardening.

The researchers adjusted their data for factors such as weight and hormone use but not for diet and smoking, since neither factor appeared to be that that different among active and inactive women, Rockhill said.

Louise Brinton, chief of the environmental epidemiology branch at the National Cancer Institute, said the findings are more likely to be accurate than some other studies because the women were asked about their exercise habits when they were actually exercising. Other studies have asked participants to remember how active they were in the past.

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