Plasma leptin in female athletes: relationship with body fat, reproductive, nutritional, and endocrine factors

The relationship of leptin to thyroid and sex hormones, insulin, energy int ake, exercise energy expenditure, and reproductive function was assessed in 39 female athletes. They comprised elite athletes who were either amenorrh eic (EAA; n = 5) or cyclic (ECA; n = 8) and recreationally active women who were either cyclic (RCA; n = 13) or taking oral contraceptives (ROC; n = 1 3). Leptin was significantly lower in EAA (1.7 +/- 0.2 ng/ml) than in ECA ( 2.9 +/- 0.3 ng/ml), RCA (5.8 +/- 0.9 ng/ml), and ROC (7.4 +/- 1.3 ng/ml). H ypoleptinemia in EAA was paralleled by reductions (P < 0.05) in caloric int ake, insulin, estradiol, and thyroid hormones. Leptin increased by 40-46% ( P < 0.05) in the luteal phase of the menstrual cycle in RCA and EGA. Plasma leptin was similar in the placebo and active pill phases in ROC despite a significant increase in ethinylestradiol. Leptin correlated (P < 0.05) with triiodothyronine and insulin but not with estrogen, energy intake, or exer cise energy expenditure. These data suggest that in female athletes 1) lept in may be a metabolic signal that provides a link between adipose tissue, e nergy availability, and the reproductive axis and 2) sex hormones do not di rectly regulate leptin secretion.