The more exercise, the lower the risk of breast cancer

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· THE QUESTION While some breast cancer risk factors (family history, race and age) can't be altered, women can control others. Might physical activity be one of them?

· THIS STUDY analyzed data on 36,363 post-menopausal women, who averaged about 62 years old; nearly all of them were white. The women recorded physical activity they did during their free time. Over the next 18 years, 2,548 of the women were found to have breast cancer. Those who exercised the most (participating in vigorous activity two or more times a week or moderate activity four times a week) were 14 percent less likely to have breast cancer than were women who exercised the least (any sort of physical activity less than once a week). When weight loss was taken into account (overweight is a risk factor for breast cancer), the benefit was 9 percent in favor of the more-frequent exercisers.

The benefit appeared especially strong for women with the more aggressive estrogen receptor-positive tumors, cancer that is fueled by the hormone estrogen; in this group, the most-frequent exercisers had a 33 percent lower risk than those who exercised the least.

· WHO MAY BE AFFECTED BY THESE FINDINGS? Post-menopausal women. The risk of developing breast cancer increases with age. Nearly 80 percent of women found to have breast cancer are 50 or older when the cancer is diagnosed.

· CAVEATS Whether the findings apply to other than white women remains unclear. Exercise data were based on the women's recall and did not include physical activity related to work.

· FIND THIS STUDY Dec. 11/25 issue of the Archives of Internal Medicine; abstract available at http://www.archinternmed.com.