The risk of breast cancer diminishes rapidly after postmenopausal women begin to exercise, even if their daily activity is no more than a half hour walk. A study from France found that women who began exercising for at least four hours a week in the four years during which the data was collected had a 10 percent lower risk of breast cancer than women who didn’t exercise during that period. The risk of breast cancer also diminished in women who spent two hours a week cycling or engaging in other sports. However, the cancer risk was not reduced among women who reported performing this amount of exercise during five to nine years before they took part in the study, but who were less active during the four years of the study itself. The researchers noted that their findings addressed the question of how rapidly exercise impacts breast cancer risk and determined that the risk remains 10 percent lower in physically active women as long as they continue to exercise, but not after they stop. Earlier studies have shown that physical activity can also boost survival rates for women who have already been diagnosed with the disease.
Agnès Fournier et al, “Recent Recreational Physical Activity and Breast Cancer Risk in Postmenopausal Women in the E3N Cohort.” Cancer Epidemiology Biomarkers & Prevention, 2014; DOI: 10.1158/1055-9965.EPI-14-0150