June 16 (HealthDay News) -- A method for predicting which teenage female athletes are at risk to stop menstruating -- an important factor in causing the bones to lose mass -- may have been found, according to a preliminary study.

Up to 25 percent of female high school athletes develop amenorrhea, or absence of menstruation, compared with 2 percent to 5 percent in the general population, researchers from Massachusetts General Hospital in Boston found.

The report was expected to be presented Monday at The Endocrine Society's annual meeting in San Francisco.

Intense exercise and caloric restriction, which cause an energy deficit in the body, are thought to cause the menstrual irregularities in athletes.

Amenorrhea can cause infertility and early onset of low bone density, which may increase the risk of broken bones.

The researchers measured levels of various hormones in females aged 12 to 18. In particular, levels of ghrelin were examined. Ghrelin is a hormone that can cause reduce secretion of hormones that regulate ovarian and menstrual function. People with anorexia nervosa, another condition of severe energy deficit, have elevated ghrelin levels.

The scientists found that ghrelin levels were higher in athletes who were not menstruating than in those who were having their periods or were non-athletic females. The athletes with higher ghrelin levels also 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," the study's presenter, Dr. Madhusmita Misra, a pediatric endocrinologist at Massachusetts General Hospital, said in a prepared statement.

"In addition, ghrelin may be an important link between an energy deficit state and the hormones that regulate menstrual function."

More information

The National Institute of Child Health and Human Development has more about  amenorrhea.

SOURCE: The Endocrine Society, news release, June 16, 2008