Aerobic exercise and breast cancer risk

Women who engage in regular aerobic exercise before menopause metabolize the hormone estrogen more effectively, and probably drive down their risk for breast cancer, a new study finds. (Eric Santucci)

There's a fair amount of circumstantial evidence that regular exercise reduces a woman's risk of developing breast cancer. But contradictory findings, and lingering questions as to how physical activity would work to ward off breast cancer, have clouded the picture, apparently leaving some women on the couch, waiting for that scientific fog to lift.

C'mon ladies, get up and take the girls to the gym. A new study shows that without making any other changes in their lifestyles, young women who got an average of 30 minutes of moderate-to-vigorous aerobic exercise five days a week showed significantly improved estrogen metabolism after just 16 weeks. And the measure of estrogen metabolism that changed most was the same one that past studies have shown is most associated with breast cancer risk.

A woman's risk of developing breast cancer is closely tied to her lifetime exposure to estrogen, a hormone that rises through a woman's years of peak fertility, and whose presence in the body can be boosted by certain medications and medical conditions, and, researchers surmise, by excess fat deposits, sedentary behavior, or both. The current study takes a key step in parsing out the role of exercise in moderating estrogen's effects.

Compared with similar women who made no changes in their exercise routines, the premenopausal women (average age of 25) who achieved an average weekly tally of 127 minutes of aerobic exercise also saw significant increases in lean muscle mass, loss of fat mass and better body composition. 

But the principal strength of the latest study, published Tuesday in the journal Cancer Epidemiology, Biomarkers & Prevention, is that it uses new techniques and measurements to provide "the most comprehensive analysis on the effects of exercise on estrogen metabolism to date." Among exercising women, it finds an increase in "good" estrogen metabolites, which in other studies have been closely linked to decreases in breast cancer risk.

Mindy Kurzer, a University of Minnesota professor of food science and nutrition and lead author of the study, said there's still more work to be done to understand the mechanisms that link aerobic exercise and breast cancer. But there's no shortage of evidence already that it can drive down the risk of heart disease--a far more probable threat to a woman as she ages. 

So why wait?