Energy expenditure and plasma F2-isoprostanes across the menstrual cycle

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.

We investigated the relation between energy expenditure and plasma free F2-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. F2-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.

Habitual energy expenditure was positively associated with F2-isoprostane concentration (adjusted difference in median F2-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 F2-isoprostane concentration (category trend, P=0.50 and P=0.18, respectively).

These results suggest that higher habitual energy expenditure may be associated with higher concentration of F2-isoprostanes in healthy, reproductive-aged women. Estradiol concentration changes during the menstrual cycle do not seem to influence this relationship.