Studies have shown that being physically active may reduce a woman's risk for developing breast cancer, although many questions have yet to be answered. For example, these studies have hinted that very high activity levels may not be as beneficial for reducing breast cancer risk as moderate activity levels.
In southern Germany, approximately 350 women with premenopausal breast cancer and nearly 900 women free of cancer participated in a study in which they reported on multiple types of activity, between the ages of 12-19 and 20-30. Activities included different sports; household tasks; occupational activities; walking; and cycling.
Moderate activity levels reduced breast cancer risk the most (32%), with very high activity levels actually increasing risk, compared to inactive women. Women who reported bicycling the most (the equivalent of at least three hours per week at moderate intensity) reduced their risk for breast cancer by 34% in this study in the American Journal of Epidemiology. Being active reduced cancer risk regardless of sports participation.
The authors conclude that moderate activity may effectively reduce breast cancer risk, whereas high activity does not, because while the former may strengthen the immune system, the latter may depress it. Most women need not worry about being overly active, though, as this only applies to a small percentage of the most active women. A fairly vigorous workout several times per week, especially riding a bicycle, may be a good way to reduce your risk for breast cancer.
Steindorf K, Schmidt M, et al. Case-control study of physical activity and breast cancer risk among premenopausal women in Germany. American Journal of Epidemiology 2003:157(2), pp. 121-130.
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