NEW YORK (Reuters Health) – Bone health may be at risk when young female athletes stop menstruating, study findings suggest.

Researchers found that among 57 athletic and non-athletic teenage girls, athletes who had stopped getting their periods had lower bone density than their peers.

The findings underscore the importance of proper nutrition in athletic teenage girls, the researchers report in the journal Pediatrics.

Inadequate calorie intake and low body fat are believed to be the prime culprits in amenorrhea, or absence of menstrual periods, in female athletes.

“There is a critical window in time through the pubertal period when bone mass is optimized,” Dr. Madhusmita Misra, the senior researcher on the new study, told Reuters Health.

Amenorrhea indicates that the body is not making enough of the hormones necessary to optimize bone mass. This leads to a decreased rate of bone mass accrual at the age when bone mass should be moving toward peak levels, explained Misra, of Massachusetts General Hospital and Harvard Medical School in Boston.

Among non-menstruating young athletes, Misra said, “subsequent peak bone mass could be suboptimal and may impact bone health in later life.”

For their study, Misra and her colleagues assessed bone density in two groups of athletes between the ages of 12 and 18 — mostly runners — and a group of non-athletes of similar age and body composition.

Twenty-one of the athletes had stopped menstruating, while 18 of the athletes had regular menses — as did the 18 non-athletes.

Misra’s team found that compared with both the non-athletes and athletes who were menstruating, amenorrheic athletes had lower overall bone density.

Moreover, a much larger proportion of the non-menstruating athletes (38 percent) had lower bone density at the spine compared with the other two groups (11 percent in each).

While more studies are needed to see how athletes’ amenorrhea affects their long-term bone health, the current findings emphasize “the importance of optimizing nutritional and menstrual status in athletes,” Misra’s team writes.

“It is very important for athletes to maintain their menstrual cycles, and this is even more important for the adolescent athlete,” Misra noted.

Among the potential benefits of exercise, she and her colleagues point out, is that it can build bone mass. Amenorrhea, however, may negate that.

SOURCE: Pediatrics, June 2008.