A small experiment has concluded that twice daily injections of the hormone leptin, best known to regulate appetite and weight, can jump-start an idling reproductive system. Doctors found that the treatment restored menstruation in five of eight female athletes who had become so lean they had stopped having their periods. Leptin is a naturally occurring hormone produced by fat cells, so athletes, dancers and other thin people may have less of it. Leptin is also being studied for its role in obesity.
