Aerobic Exercise, Estrogens, and Breast Cancer Risk in Pre-Menopausal Women

Abstract

PURPOSE: Currently known risk factors for breast cancer are difficult to control and modify and therefore, there is a need to identify alternative risk factors that are more suitable for intervention, especially among young women. The WISER study, Women in Steady Exercise Research, and the pilot study that proceded it investigate the effect of aerobic exercise on sex hormone levels in healthy premenopausal women. METHODS: The WISER study is a randomized, exercise-controlled clinical trial that is randomizing 320 sedentary, healthy (BMI 18-40kg/m2), eumenorrheic, premenopausal women aged 18 to 30 years old into an exercise or no-exercise control group. Intervention subjects exercise aerobically for 30 minutes, 5 times a week during 4 menstrual cycles in which the workout intensity increases every four weeks by 5% of their age-predicted maximal heart rate until it reaches 80%-85%. The effect of aerobic exercise on blood sex hormones, urinary estrogen metabolites, menstrual cycle characteristics, ovulation status, measures of fitness (time to 85% max heart rate, MET-h/week), and body composition are being measured at baseline and follow-up. The study design for the completed pilot study in 15 women was identical, except for the lack of a comparison group. RESULTS: In the WISER pilot study, after 15 weeks of aerobic exercise, there were significant reductions in body weight (-1.7 %, p <0.007), BMI (-2.4%, p< 0.01), and fat mass (-6.5%, p<0.04). In contrast, a significant 10.6% increase in submaximal fitnesss (p< 0.004) was attained through the intervention. No significant changes in endogenous estrogens were observed, though the pattern of changes was consistent with a reduction of cancer risk. Levels of estrone, 16-α-hydroxyestrone, estriol, 4-hydroxyestrogens, and the ratio of 2-to-4 hydroxyestrogens were reduced while that of 2-hydroxyestrogens and the ratio of 2-to-16-α-hydroxyestrone increased. CONCLUSIONS: Results from the pilot study showed that aerobic exercise training at the dose currently recommended for health promotion and disease prevention results in significant reductions in body fat in young eumennorheic women. Changes in estrogens were in the expected direction, though not significant. The larger, ongoing WISER trial was designed to further investigate the effects of aerobic exercise training on endogenous sex hormones and other breast cancer biomarkers. The WISER study will contribute to a better understanding of the effect of aerobic exercise on the hormonal and physiological profiles of healthy, sedentary, young women and help determine the efficacy of such an intervention on breast cancer risk prevention.