Amenorrhea, or absence of menstruation, occurs in as many as 25 percent of female high school athletes, compared with 2 to 5 percent in the general population, according to the study's presenter, Madhusmita Misra, MD, a pediatric endocrinologist at Harvard-affiliated Massachusetts General Hospital, Boston.

Amenorrhea in athletes is known to cause infertility and early onset of low bone density and may increase the risk of breaking bones. Evidence suggests that intense exercise associated with caloric restriction, and therefore a state of energy deficit, is most responsible for menstrual irregularities among athletes.

In females ages 12 to 18, Misra and her colleagues measured levels of various hormones, including ghrelin. Giving ghrelin to animals and humans has been shown to cause impaired secretion of hormones that regulate ovarian and menstrual function, and ghrelin levels are elevated in people with anorexia nervosa, another condition of severe energy deficit, she said. Until now, ghrelin levels have not been studied in teenage athletes in relation to ovarian hormones.

The researchers studied 21 teenage athletes with amenorrhea, 19 normally menstruating athletes and 18 nonathletic girls. The body mass index, a measure of body fat, was lower in the amenorrheic girls than in the other two groups, but overall these athletes were not underweight. All girls were more than 85 percent of the ideal body weight for their ages. The amenorrheic group reported similar levels of physical activity as the normally menstruating group, and both groups of athletes reported more physical activity than the non-athletic group.

Even after controlling for BMI, the research team found that ghrelin levels 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.

"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."

They plan to further study the role of ghrelin in menstrual function in more subjects and over an extended time.

The National Institutes of Health funded this study.