We have known for a long time that regular aerobic exercise lowers the risk of breast cancer and now we have some wonderful science that shed some powerful light on how regular physical activity benefits breast health.
For this study, researchers assigned 391 healthy, but sedentary pre-menopausal women to one of two groups. One group engaged in 30 minutes of moderate to vigorous aerobic activity five times a week, while the control group remained sedentary and did not exercise. The scientists measured urine levels of estrogen metabolites in all study participants before and several times after the 16-week study period. The urine estrogen metabolites from the exercise group changed over the study period and were different from the sedentary group.
Specifically, the estrogen metabolites in the exercise group were of the type that are breast cancer protective. The researchers concluded that regular aerobic activity like brisk walking alters estrogen metabolism favoring the formation of estrogen metabolites that lower breast cancer risk.