For sedentary postmenopausal women, moderate to vigorous exercise for a year reduced levels of estradiol, researchers said.
The reductions, compared with those achieved by controls, were modest but significant and were consistent with a lower risk for breast cancer, according to Christine Friedenreich, PhD, of Alberta Health Services in Calgary, and colleagues.
The finding, from a randomized trial, is evidence that such women — sedentary and mostly overweight — can “achieve and sustain high levels of aerobic exercise,” the researchers reported online in the Journal of Clinical Oncology.
Observation suggests that increased physical activity is linked to lower breast cancer risk, but exactly how remains unclear, the researchers noted. One plausible mechanism, they said in the journal, is modification of the sex hormones.
To investigate the issue, they enrolled 320 postmenopausal women, ages 50 to 74, in a one-year trial; 160 women were randomly assigned to 225 minutes a week of aerobic exercise, the remaining 160 maintained their usual level of activity.