Effects of Exercise and Cardiorespiratory Fitness on Estrogen Metabolism in Postmenopausal Women.

BACKGROUND: Lowering endogenous estrogen levels is one mechanism whereby physical activity may lower postmenopausal breast cancer risk. Several prospective studies have suggested that increased 2-hydroxylation of estrogens may also reduce postmenopausal breast cancer risk, but whether or not exercise alters estrogen metabolism through this mechanism is unclear.
METHODS: We measured total circulating concentrations of parent estrogens (estrone and estradiol) and 13 estrogen metabolites, including glucuronidated, sulfated, and unconjugated forms, by stable isotope dilution LC/MS-MS in 153 postmenopausal women randomized to 12 months of moderate-to-vigorous exercise and 153 controls. We also explored associations with cardiorespiratory fitness measured by treadmill.
RESULTS: Although women randomized to exercise averaged 178 minutes/week of exercise over 12 months, their cardiorespiratory fitness was 13% greater than controls at 12 months (P = 0.0001), and total estradiol was reduced by 10% (P = 0.04); there were no statistically significant effects of exercise on circulating concentrations of estrogen metabolites in the 2-, 4-, or 16-pathways, or on the 2-pathway/parent estrogens ratio. However, we observed a statistically significant association between increased fitness and reduced concentration of 2-pathway metabolites (P < 0.05).
CONCLUSIONS: We found no evidence that 12 months of moderate-to-vigorous exercise or increased fitness changed estrogen metabolism in a way that might reduce breast cancer risk. IMPACT: The protective effect of exercise on postmenopausal breast cancer is unlikely to be mediated by changes in estrogen metabolism. ©2018 American Association for Cancer Research.

RCT Entities:   Population Interventions Outcomes