The purpose of this study was to investigate the role of leptin on reproductive hormones and ovulation.

The BioCycle Study (2005-2007) followed 259 healthy premenopausal women not using hormonal contraceptives for ≤2 menstrual cycles (n = 509 cycles). Serum leptin, estradiol, progesterone, luteinizing hormone (LH), follicle-stimulating hormone, and testosterone were measured ≤8 times per cycle. The association of time-varying leptin and reproductive hormones over the cycle was estimated with the use of linear mixed models that were adjusted for percent body fat and age with inverse probability weighting for time-varying physical activity, caloric intake, and other reproductive hormones. The odds ratio for sporadic anovulation (n = 42 cycles) was estimated with the use of generalized linear models that were adjusted for percent body fat and age.

Geometric mean serum leptin levels increased from menses to the late luteal phase (16.7-20.4 ng/mL; P < .01), with a mid-cycle peak (21.7 ng/mL) at the time of the LH surge (P < .01). A 10% higher leptin level across the menstrual cycle was associated with higher estradiol levels (2.2%; 95% CI, 1.5–3.0), luteal progesterone levels (2.1%; 95% CI, 0.5–3.7), ovulatory LH levels (1.2%; 95% CI, 0–2.3), testosterone levels (0.6%; 95% CI, 0.3–0.9), and lower follicle-stimulating hormone levels (–0.7%; 95% CI, –1.1 to –0.4). Leptin at the time of the expected LH surge was moderately inversely associated with sporadic anovulation (per log increase in leptin; adjusted odds ratio, 0.58; 95% CI, 0.28–1.22).

The association that was observed between leptin level and reproductive function points to a possible relationship between serum leptin level and enhanced fertility.