Women Athletes Warned of Premature Bone Loss : Health: Researcher says females who exercise a lot while eating a little should beware if menstrual cycles become irregular or cease.
Eating very little while exercising a lot can keep a woman thin, but overdoing it may damage her reproductive ability and her bones, a researcher says.
The lack of enough available calories to meet a hard-working body’s needs sets up a cascade of hormonal changes that results in physical changes similar to those of anorexia, said Ann Loucks, an associate professor of physiology at Ohio University in Athens.
Women with this caloric deficit tend to have irregular or missing menstrual cycles, and this could keep them from conceiving, Loucks said. They also can lose bone minerals, which may lead later in life to the brittle-bone disease, osteoporosis, she said. She reported on her research recently at a National Institutes of Health workshop in Bethesda, Md.
On the other hand, Loucks’ work indicates that exercise itself is not the entire problem, so female athletes could prevent trouble by eating more and by being less concerned about whether they are thin enough.
A big imbalance between energy demand and the amount of calories available to meet it seems to drive down levels of luteinizing hormone. This hormone, which is made by the pituitary gland, sends chemical signals that result in the release of the female hormones estrogen and progesterone, Loucks said.
In one study, Loucks created deficits of more than 1,000 calories by putting women on diets, having them exercise, or both. She and her colleagues took blood samples every 10 minutes for 24 hours. The women she studied had fewer pulses of luteinizing hormone when the energy gap was greater than 1,000 calories, the study found.
But this doesn’t indicate that 1,000 calories is some kind of cutoff, Loucks said. She doesn’t yet know exactly the minimum caloric level needed to allow enough luteinizing hormone to continue the menstrual cycle, she said.
The researchers also don’t know whether the deficit affects luteinizing hormone production directly or whether it affects another part of the body’s hormonal systems, which then trigger fewer pulses of this hormone.
But it is clear that a shortage of luteinizing hormone affects a woman’s periods, and thereby her ability to conceive, Loucks said.
Because estrogen also affects the level of calcium in the bone, a shortage of luteinizing hormone could create a chain of hormonal events that robs bones of calcium, Loucks said. The result in its worst cases mimics the effects of menopause, bringing the bone density loss of midlife to women still in their reproductive years.
“She’s carefully built her case,” said Barbara L. Drinkwater, a leading researcher in the effects of exercise on bone density and menstruation. “I think she is on the right track.”
Female athletes should be concerned if they start missing periods, said Drinkwater of Pacific Medical Center in Seattle. Women who go six months without a normal menstrual cycle can have measurable bone loss, Drinkwater said.
Assuming Loucks is right, calcium supplements or estrogen replacement therapy to fight the loss of bone is only a partial solution to what is really a nutritional problem, Drinkwater said.
“The women have a red flag, so to speak,” Drinkwater said. “If their menses become irregular or actually cease, then they know it’s time to do something.”
But for many athletes, the power to act is largely out of their control, Drinkwater said. A ballet dancer may have to stay ultra-thin or lose her place in the company, she said. And a collegiate athlete on a scholarship may have to follow her coach’s wishes exactly or lose the money that keeps her in college, the researcher said.
And some women see the interruption of the menstrual cycle as a form of birth control, Drinkwater said: “It’s not an occasion for them to be happy about, as too many athletes are.”