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

TLDR

The study examined how leptin relates to thyroid and sex hormones, insulin, energy intake, exercise energy expenditure, and reproductive function in 39 female athletes. Participants included elite amenorrheic and cyclic athletes and recreationally active cyclic and oral‑contraceptive‑using women, with group sizes of 5, 8, 13, and 13 respectively. Leptin was markedly lower in amenorrheic elite athletes and correlated with reduced caloric intake, insulin, estradiol, and thyroid hormones, while it rose 40–46% during the luteal phase in cyclic groups, correlated with triiodothyronine and insulin but not with estrogen, energy intake, or exercise expenditure, indicating leptin links adiposity, energy availability, and reproduction but is not directly regulated by sex hormones.

Abstract

The relationship of leptin to thyroid and sex hormones, insulin, energy intake, exercise energy expenditure, and reproductive function was assessed in 39 female athletes. They comprised elite athletes who were either amenorrheic (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 = 13). 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). Hypoleptinemia in EAA was paralleled by reductions ( P < 0.05) in caloric intake, insulin, estradiol, and thyroid hormones. Leptin increased by 40–46% ( P < 0.05) in the luteal phase of the menstrual cycle in RCA and ECA. 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 exercise energy expenditure. These data suggest that in female athletes 1) leptin may be a metabolic signal that provides a link between adipose tissue, energy availability, and the reproductive axis and 2) sex hormones do not directly regulate leptin secretion.