Energy deficit interrupts periods: athletic girls face hormone imbalance from too few calories

Science News, July 19, 2008 by Nathan Seppa

SAN FRANCISCO -- Roughly one-fourth of high school and college female athletes stop having periods at some point, far more than the 2 to 5 percent rate in women overall, surveys have shown. A new study reveals a hormone imbalance that might help doctors identify girls at risk of losing their monthly cycle.

A stoppage of periods, amenorrhea, results in temporary infertility and can reduce bone density. Previous research indicates that amenorrhea strikes girls and young women who exercise extensively but have a calorie intake that doesn't satisfy their bodies' needs, leading to what scientists call a state of "energy deficit." Amenorrhea results from internal priorities, enforced by hormones, that allot the athletes' nutrients. Researchers say that the body's reproductive system loses out in a tug-of-war for calories.

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The new study looked at blood levels of two appetite-regulating hormones, ghrelin and leptin, in 40 female athletes and 18 non-athletic females, all 12 to 18 years old. Ghrelin is known for stimulating appetite and leptin for signaling satiety, but the study suggests they also influence estrogen manufacture and secretion.

About half the athletes had amenorrhea. These girls also had higher ghrelin levels and lower leptin levels compared with the athletes who were still having periods, says study coauthor Madhusmita Misra, an endocrinologist at Harvard Medical School and Massachusetts General Hospital in Boston. That means changes in ghrelin and leptin may throw off production of estrogen or other reproductive hormones necessary for having regular monthly cycles, says Misra, who presented the findings June 16 at a meeting of the Endocrine Society.

The researchers also found that the girls with amenorrhea had significantly poorer bone density than the others.

While the infertility is easily reversed, the reduction in bone density poses a greater problem. "These might be girls who will be at risk later in life," says Nanette Santoro of the Albert Einstein College of Medicine in New York.