The reason for menstrual shutdown, particularly in athletes who are not thin enough to be diagnosed with anorexia nervosa, is not clear. Medical researchers point their fingers at hormones including leptin, an appetite suppressor made in fat cells and luteinizing hormone that pulses to jump start monthly cycles. The idea is that these and other hormones signal the body when it is experiencing an energy deficit. The body, in turn, shuts down its monthly cycles. The body knows: a woman shouldn’t be having a baby when she is starving. And so our active girls as they kick their goals or lob their jump shots are, in essence, playing with an evolutionary kill-switch that controls survival of the species.

Maybe. While the causes of athletic amenorrhea are unclear, the consequences are certain. Lack of periods leads to frightening bone loss at an age where girls need to build their bones to ward off osteoporosis late in life. The phenomenon, known as “female athlete triad,” refers to three problems that go hand-in-hand: low energy availability, menstrual disorders, and weak bones.

The Harvard researchers, led by pediatric endocrinologist Madhusmita Misra, MD, at Massachusetts General Hospital, Boston had another idea on how to tackle the problem. They focused on a new player in the world of endocrinology and reproduction: a stomach-secreted hormone called ghrelin, known to spur appetite. Researchers have found that if they give ghrelin to animals and humans, not only stirs hunger; it also blunts the production of hormones that regulate ovarian and menstrual function. Another factoid: ghrelin levels are elevated in people with anorexia nervosa, which may be why they feel a voracious appetite, constantly think about food, even dream about it. Tragically, people with anorexia will not let themselves eat the food, however.

That in mind, Misra and her colleges studied 21 teenage athletes with amenorrhea, 19 normally menstruating athletes and 18 nonathletic girls. Not surprising, body mass index, a measure of body fat, was lower in the amenorrheic girls than in the other two groups. Still, these athletes were not underweight in the range of anorexia, less than 85 percent of the ideal body weight for their ages. So why did some of the girls lose their periods while other did not?

The answer may be ghrelin. The levels of that hormone were higher in athletes that were not menstruating than in either of the other two groups. The data also showed that athletes with higher ghrelin levels had lower levels of the sex hormones estrogen and testosterone. So those, too, could be feeding into menstrual shutdown.

Whatever the mechanisms, “These findings suggest that hormonal disorders may explain why amenorrhea occurs in some but not all adolescent athletes,” Misra said. “In addition, ghrelin may be an important link between an energy deficit state and the hormones that regulate menstrual function.”

Indeed. We would welcome the information. Maybe down the road, ghrelin supplements could restore menstrual function to these young girls at risk. It’s worth a shot. Our girls should be free to pursue their athletic dreams. At the same time, we should encourage them to eat healthy while being active. For those who lose their periods, bone loss is a debilitating consequence that could plague them in years to come. For my daughter’s sake, and my own, having experienced amenorrhea until the age of 33, I applaud these studies and hope for more.

The results were presented today, June 16, 2008, at the Endocrine Society’s 90th Annual Meeting in San Francisco.