Background: 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.
Methods: 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.
Results: 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).
Conclusions: 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.
Trial registration: clinicaltrials.gov identifier: NCT01435005.
Keywords: Breast Cancer; Physical Activity; Prolactin; Randomized Controlled Trial.