Abstract
BACKGROUND: Low concentrations of leptin secondary to low body fat or other modulators are thought to be a key signal whereby an energy deficit suppresses the reproductive axis in exercising women resulting in functional hypothalamic amenorrhea (FHA). The purpose of this study was to first examine leptin concentrations in exercising women with and without FHA to address whether there is a threshold concentration of leptin below which reproductive function is suppressed. Secondly, we examined the role of adiposity and other possible modulators of leptin to ascertain whether leptin regulation differs depending on reproductive status.
METHODS: This study assessed 50 exercising, premenopausal women (aged 18-30 years) over the course of one menstrual cycle (eumenorrheic women) or one 28-day monitoring period (amenorrheic women). Quantification of daily urinary ovarian steroids and menstrual history were used to determine menstrual status. Body composition was assessed using dual energy X-ray absorptiometry, and leptin was determined by enzyme-linked immunoassay. Key modulators of leptin such as serum insulin concentration, carbohydrate intake, glucose availability, indirect indices of sympathetic nervous activity and other factors were assessed using linear regression.
RESULTS: Percentage body fat (%BF) (21.0 +/- 1.0 versus 26.8 +/- 0.7%; P < 0.001) and leptin concentration (4.8 +/- 0.8 versus 9.6 +/- 0.9 ng/ml; P < 0.001) were lower in the exercising women with amenorrhea (ExAmen; n = 24) compared with the exercising ovulatory women (ExOvul; n = 26). However, the ranges in leptin were similar for each group (ExAmen: 0.30-16.98 ng/ml; ExOvul: 2.57-18.28 ng/ml), and after adjusting for adiposity the difference in leptin concentration was no longer significant. Significant predictors of log leptin in ExAmen included %BF (beta = 0.826, P < 0.001), log insulin (beta = 0.308, P = 0.012) and log glycerol (beta = 0.258, P = 0.030), but in ExOvul only %BF predicted leptin.
CONCLUSIONS: These data suggest that leptin concentrations per se are not associated with FHA in exercising women, but the modulation of leptin concentrations may differ depending on reproductive status.