Adiposity and sex hormones across the menstrual cycle: the BioCycle Study

Objective To investigate the influence of adiposity on patterns of sex hormones across the menstrual cycle among regularly menstruating women. Subjects The BioCycle Study followed 239 healthy women for 1–2 menstrual cycles, with up to 8 visits per cycle timed using fertility monitors. Methods Serum estradiol (E2), progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and sex hormone binding globulin (SHBG) were measured at each visit. Adiposity was measured by anthropometry and by dual energy x-ray absorptiometry. Differences in hormonal patterns by adiposity measures were estimated using nonlinear mixed models, which allow for comparisons in overall mean levels, amplitude (i.e. lowest to highest level within each cycle), and shifts in timing of peaks while adjusting for age, race, energy intake, and physical activity. Results Compared to normal weight women (n=154), obese women (BMI≥30 kg/m2, n=25) averaged lower levels of progesterone (−15%, P=0.003), LH (−17%, P=0.01), FSH (−23%, P=0.001) and higher free E2 (+22%, p=0.001) across the cycle. To lesser magnitudes, overweight women (BMI: 25–30, n=60) also exhibited differences in the same directions for mean levels of free E2, FSH, and LH. Obese women experienced greater changes in amplitude of LH (9%, p=0.002), and FSH (8%, p=0.004), but no differences were observed among overweight women. Higher central adiposity by top compared to bottom tertile of trunk-to-leg fat ratio by DXA was associated with lower total E2 (−14%, p=0.005) and FSH (−15%, p=0.001). Peaks in FSH and LH occurred later (~0.5 day) in the cycle among women with greater central adiposity. Conclusion Greater total and central adiposity were associated with changes in mean hormone levels. The greater amplitudes observed among obese women suggest compensatory mechanisms at work to maintain hormonal homeostasis. Central adiposity may be more important in influencing timing of hormonal peaks than total adiposity.