Energy Expenditure and Plasma F2-Isoprostanes across the Menstrual Cycle

RUDRA, C. B., J. WACTAWSKI-WENDE, K. M. HOVEY, R. W. BROWNE, C. ZHANG, M. L. HEDIGER, and E. F. SCHISTERMAN. Energy Expenditure and Plasma F-2-Isoprostanes across the Menstrual Cycle. Med. Sci. Sports Exerc., Vol. 43, No. 5, pp. 785-792, 2011. Introduction: Habitual energy expenditure seems to favorably alter oxidant/antioxidant balance. Sparse evidence suggests that hormones that fluctuate during the menstrual cycle, particularly estrogens, may influence concentrations of oxidative biomarkers and their relation to energy expenditure. Methods: We investigated the relation between energy expenditure and plasma free F-2-isoprostane concentrations in 259 healthy, regularly menstruating 18- to 44-yr-old participants of the BioCycle Study. Habitual energy expenditure was measured using a baseline International Physical Activity Questionnaire and categorized as low, moderate, or high. Women were followed for one or two subsequent menstrual cycles. Past-week and past-day physical activity were measured during follow-up using questionnaires and diaries, respectively. F-2-isoprostane concentrations were measured in blood samples collected at both menses (approximate cycle day 2; low serum estradiol concentration) and the late follicular phase (approximate cycle day 12; peak estradiol concentration). Generalized estimating equations were used to model the energy expenditure/isoprostane association, adjusting for confounders. Results: Habitual energy expenditure was positively associated with F-2-isoprostane concentration (adjusted difference in median F-2-isoprostane, high versus low energy expenditure: 17.4%; 95% confidence interval (CI) = 3.3%-31.4%). This association was not modified by cycle phase (interaction, P = 0.61) or differences in peak estradiol concentration across women (interaction, P = 0.20). Past-week and past-day physical activity measures were not associated with F-2-isoprostane concentration (category trend, P = 0.50 and P = 0.18, respectively). Conclusions: These results suggest that higher habitual energy expenditure may be associated with higher concentration of F-2-isoprostanes in healthy, reproductive-aged women. Estradiol concentration changes during the menstrual cycle do not seem to influence this relationship.