Physical activity, body size, and estrogen metabolism in women

Objectives: Physical activity has demonstrable effects on estrogen levels in pre- and postmenopausal women. Increased oxidation of estrone to 2-hydroxyestrone (2HE) relative to 16alpha-hydroxyestrone (16HE) has been hypothesized to reduce breast cancer risk, but little is known about the effect of physical activity and body size in relation to the ratio of 2HE and 16HE in women. We examined these relationships in cross-sectional analyses of 157 North American and Chinese women. Methods: Physical activity was assessed using validated questionnaires. Adiposity was assessed as body mass index (BMI, kg/m(2)) and by anthropometric methods (% body fat). Estrone metabolites, 2HE and 16HE, were determined from urine via ELISA. Results: Regression analyses on the 2HE/16HE ratio revealed an interaction between leisure-time physical activities and adiposity in both North American and Chinese women (p less than or equal to 0.05). Women reporting low levels of leisure-time physical activity who had higher BMI levels had 2HE/16HE ratios that were lower than their lean counterparts. In contrast, women with higher BMI levels that were physically active maintained higher 2HE/16HE ratios. Conclusion: These findings suggest that physical activity participation has the potential to modify the adverse effect of increased adiposity on estrogen metabolism in North American and Chinese women.