Strenuous physical activity like swimming, aerobics and running might reduce the risk of breast cancer in women. However, it is not clear how hard or long do women need to exercise. Researchers from the University of Southern California in Los Angeles said exercise might reduce the risk of breast cancer through changes in metabolism and the immune system, and by reducing weight gain. The study involved 110,599 women in California whose health records were tracked from 1995 onward. A total of 2,649 of the women were diagnosed with invasive breast cancer, and 593 with early-stage forms of the disease, till 2002. Women who said they engaged in strenuous activity for more than five hours a week had a 20 percent lower risk of invasive breast cancer and a 31 percent lower risk of early stage breast cancer, compared to women who participated in less than 30 minutes of such activity every week. The study looked at the cumulative effect of exercise over time, as opposed to women's reports of whether they had exercised shortly before being diagnosed with breast cancer. The findings provide additional evidence supporting a protective role for long-term strenuous exercise on risk of breast cancer, whereas the beneficial effects of moderate activity are less clear.
Archives of Internal Medicine,
February 2007