Objective habitual physical activity and estradiol levels in obese Latina adolescents.

BACKGROUND Lifetime physical activity (PA) is associated with decreased breast cancer (BC) risk; reports suggest that PA during adolescence contributes strongly to this relationship. PA lowers production of sex hormones, specifically estradiol, or decreases insulin resistance (IR), thereby lowering risk. Overweight Latina adolescents are insulin resistant and exhibit low levels of PA, potentially increasing their future BC risk. METHODS 37 obese Latina adolescents (15.7 ± 1.1 yrs) provided measures of PA using accelerometry; plasma follicular phase estradiol, sex-hormone binding globulin, total and free testosterone, dehydroepiandrosterone-sulfate (DHEAS); IR using HOMA-IR; and body composition via DEXA. Partial correlations and stepwise linear regressions assessed cross-sectional relationships between sex hormones, IR and PA. Body composition, and age were included a priori as covariates. RESULTS Estradiol was negatively associated with accelerometer counts per minute (CPM; r = -0.4; P = .02), percent time spent in moderate PA (%MPA; r = -0.5; P = .006), and percent time in moderate or vigorous PA (%MVPA; r = -0.5; P = .007). DHEAS was positively associated with CPM (r = .4, P = .009), %MPA (r = .3, P = .04), and %MVPA (r = .3, P = .04). Other sex hormones and IR were not associated with PA measures. CONCLUSION This study is the first to show that higher habitual PA was inversely associated with estradiol in obese adolescents.