Physical activity does not alter prolactin levels in post-menopausal women: results from a dose-response randomized controlled trial

Increased circulating levels of prolactin have been associated with increased risk of both in situ and invasive breast cancer. We investigated whether or not physical activity had a dose-response effect in lowering plasma levels of prolactin in postmenopausal women. Four hundred previously inactive but healthy postmenopausal women aged 50-74 years of age were randomized to 150 or 300 min per week of aerobic physical activity in a year-long intervention. Prolactin was measured from fasting samples with a custom-plex multiplex assay. A high compared to moderate volume of physical activity did not reduce plasma prolactin levels in intention-to-treat (Treatment Effect Ratio (TER) 1.00, 95% Confidence Interval (CI) 0.95 - 1.06) or per-protocol analyses (TER 1.02, 95% CI 0.93 - 1.13). It is unlikely that changes in prolactin levels mediate the reduced risk of breast cancer development in post-menopausal women associated with increased levels of physical activity. clinicaltrials.gov identifier: NCT01435005.