Leptin: A Link Between Energy Imbalance and Exercise-Induced Amenorrhea in Female Athletes
Up to a quarter of female athletes may experience exercise-induced amenorrhea, depending on the type of sport and the level of competition. This amenorrhea is a component of the Female Athlete Triad, a term used to describe three interrelated conditions commonly seen together in the elite female athlete: chronic dieting and/or disordered eating, amenorrhea, and decreased bone mass. Leptin, a hormone secreted by adipose tissue and believed to play a central role in eating behaviors and energy balance, is frequently diminished in athletes with exercise-induced amenorrhea. Increasing evidence points to this hormone as a critical "messenger" that enables the body's nutritional and energy status to influence its reproductive axis. One proposed model suggests that low levels of insulin, a direct effect of low glucose levels, may inhibit leptin synthesis and secretion. This decrease in leptin levels, combined with a fall in T3 thyroid hormone, may serve to suppress the reproductive axis and decrease basal metabolic rate. In the case of the amenorrheic athlete, then, falls in leptin levels may serve as neuroendocrine adaptation to insufficient energy intake, shutting down the energy-costly reproductive system (2). in a situation of perceived energy deficiency.