More Evidence That Exercise May Protect Against Breast Cancer

Exercise has been shown to offer a variety of health benefits, from preventing obesity to reducing the risk of heart disease. Now, there may be another reason to work up a sweat.

A recent study adds weight to the evidence that exercise may protect against breast cancer.

Researchers studied data from the well-known Nurses’ Health Study — a study that has followed a group of 121,701 woman registered nurses since 1976. Information about physical activity was obtained through questionnaires collected between 1980 and 1994. There were 3,137 cases of breast cancer diagnosed during that time.

Women who reported exercising moderately or vigorously for seven hours or more per week were nearly 20% less likely to develop breast cancer than those who exercised less than 1 hour per week. Walking was the most popular physical activity reported. Bicycling, swimming and aerobics were other examples of moderate or vigorous activity.

While some research has failed to find an association between physical activity and breast cancer, “the bulk of the studies have found a modest reduction in risk associated with the highest activity levels,” said lead author, Dr. Beverly Rockhill of Boston’s Brigham and Women’s Hospital.

Scientists believe that exercise may reduce the risk of breast cancer by limiting lifetime exposure to circulating ovarian hormones, namely estrogen, in women. Long-term or high exposure to estrogen stimulates the growth of some breast tumors.

“It’s long-term average physical activity that’s important,” stressed Dr. Rockhill. Exercising for 6 months and then stopping has not been shown to be effective in reducing risk, she added.

Dr. Rockhill and her colleagues suggest that future studies include estimates of lifetime exercise from all sources, including physical activity at work.

Considering the multiple benefits of exercise, study authors recommend that “all women … should be encouraged to engage in regular physical activity as part of a lifestyle to maintain good health.”

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