The effects of aerobic exercise on premenopausal levels of endogenous sex hormones and urinary estrogen metabolism

Abstract

The purpose of this doctoral project was to investigate the effects of aerobic exercise on breast cancer risk biomarkers such as endogenous sex hormone levels and urinary estrogen metabolites in premenopausal women. In this study, 391 healthy, sedentary, young eumenorrheic women were randomized to either an exercise intervention of 30 minutes of moderate-to-vigorous aerobic exercise five times a week for approximately 16 weeks (n = 212) or a usual-lifestyle sedentary control group (n = 179). Outcome measures were taken at baseline and follow-up.The study described in Chapter 2 evaluated changes in serum levels of estradiol, estrone sulfate, testosterone, progesterone, and sex hormone-binding globulin (SHBG) via radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) methods. As expected, the intervention resulted in significant increases in aerobic fitness, lean body mass, and decreases in percent body fat in women in the exercise group. No significant changes in body weight were observed between or within groups. The major finding of this study was a significant decrease in progesterone in the exercise group, albeit this change was similar to that of the control group. The lack of significant changes in sex hormone or SHBG levels due to the intervention (without a concomitant weight change) between or within groups suggest this may not be a plausible mechanism by which physical activity decreases breast cancer risk in premenopausal women.The second study described in Chapter 3 measured changes in urinary levels of estrogens (estrone [E1], and estradiol [E2]), and ten estrogen metabolites via liquid chromatography/tandem mass spectrometry (LC-MS/MS). In addition, the ratios of 2-hydroxyestrone to 16α-hydroxyestrone (2-OHE1/16α-OHE1) and 2-hydroxyestrone to 4-hydroxyestrone (2-OHE1/4-OHE1) were calculated. Although no significant changes in urinary estrogens or their metabolites were found between groups, the 2-OHE1/16α-OHE1 ratio in exercisers increased significantly (P = 0.043) compared to the control group (P = 0.045), even after adjustment for baseline values.Collectively, the results of this doctoral project suggest the positive effects aerobic exercise allegedly has on premenopausal breast cancer risk may be mediated through hormonal mechanisms that involve changes in estrogen metabolism but not necessarily changes in endogenous sex hormone levels.