We’ve long known that regular exercise - specifically aerobic exercise - reduces the risk of breast cancer, but until now, we haven’t known how physical activity confers its benefits. A team of researchers at the University of Minnesota in Saint Paul may have solved the mystery. They have confirmed that exercise influences the way women’s bodies break down (metabolize) estrogen - more activity yields more “good” metabolites that lower breast cancer risk. For their study the researchers recruited 391 sedentary but healthy, young premenopausal women and randomly assigned them to a control group or an exercise group. The women in the exercise group worked out at moderate to vigorous intensity five times a week for 16 weeks. On three consecutive days before and after the study, the researchers collected 24-hour urine samples from all the women. Analysis of these samples showed a favorable increase in the estrogen metabolites that lower breast cancer risk in the women who exercised, and no change during the 16 weeks in the women who didn’t. Some forms of estrogen stimulate the growth of many types of breast cancer cells. The study was published in the May 2013 issue of Cancer Epidemiology, Biomarkers & Prevention.
My take? Over the years, a number of studies have shown that exercise can lower the risk of breast cancer and can also boost survival rates for women who have been diagnosed with the disease. In the past, we have assumed that regular physical activity helps limit exposure to estrogen by reducing fat stores in which estrogen is produced. While defining the mechanisms that drive cancer or help prevent it increases our understanding of the disease, the bottom line remains clear: exercise can lower breast cancer risk as well promoting fitness and reducing the risk of cardiovascular disease.
Mindy S. Kurzer, et al “The Effects of Aerobic Exercise on Estrogen Metabolism in Healthy Premenopausal Women,” Cancer Epidemiology, Biomarkers and Prevention, May 2013 doi: 10.1158/1055-9965.EPI-12-1325