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 predict girls at risk of losing their monthly cycle.
A stoppage of periods, or 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 isn’t adequate to 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. The researchers find that the body’s reproductive system loses out in an evolutionary tug-of-war for calories.
In the new study, researchers studied 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. Roughly half of the athletes had amenorrhea, while the other athletes and the non-athletes still were getting periods. Ghrelin is best known for stimulating appetite and leptin for signaling satiety, but the new study suggests that they also indirectly influence estrogen manufacture and secretion.
The girls with amenorrhea 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 HarvardMedicalSchool and Massachusetts GeneralHospital in Boston. That means changes in ghrelin and leptin brought on by a negative energy balance may be important predictors of estrogen levels. Such changes may throw off production of estrogen or other reproductive hormones necessary for having regular monthly cycles, Misra says.
Girls in the amenorrhea group weighed somewhat less than those in the other two groups. After adjusting for this difference, the ghrelin effect still showed up, whereas the leptin difference didn’t, suggesting leptin levels are correlated to weight.
Meanwhile, estrogen is essential for bone growth and maintenance in women. The researchers found that the girls with amenorrhea had significantly poorer bone density than those in the other two groups.
Misra presented the findings June 16 in San Francisco at a meeting of the Endocrine Society.
In addition to further delineating the hormones underlying exercise-related amenorrhea, these findings give doctors evidence that they can use to counsel female athletes, says Nanette Santoro, a reproductive endocrinologist at the Albert Einstein College of Medicine in New York. “Athletes don’t want to stop exercising. You’re bargaining with them every step of the way,” she says. There is some suspicion that they purposefully don’t eat, either, because losing weight can make a runner faster, says Santoro, who wasn’t involved in this research.
Meanwhile, she says that while infertility caused by amenorrhea is easily reversed, the reduction in bone density poses a greater problem. “It’s not fully known whether they can correct this loss of bone,” Santoro says. “These might be girls who will be at risk later in life.”
In teenage athletes, many systems in the body compete for available energy, including cell growth, locomotion, body temperature and reproduction. Among these, reproduction is the least essential at any given moment. The results suggest that the body parcels out energy according to preset priorities. “Definitely, there is a master controller … that directs energy to other channels and keeps it away from reproduction,” Misra says.
That means that this form of amenorrhea would seem to have evolutionary underpinnings. For example, early human females who found themselves in a stressful predicament of poor nutrition and high energy expenditure would be better off not getting pregnant. “It makes all the sense in the world,” Misra says, but can have consequences for bone health.
Nowadays, she says, amenorrhea turns up most often in middle- and long-distance runners and swimmers. With the 1972 law change called Title IX that ensures girls get equal treatment to boys in educational and athletic programs, more girls have become involved in sports during adolescence. While that has been a good in general, she says, it might also explain why amenorrhea has become more prevalent in recent decades.