When Bones Are Brittle

By ANDREW PURVIS

The crippling symptoms of osteoporosis have become almost synonymous with old age. The dowager's hump, the loss of height, the painful and often debilitating fractures of the spine and hip nearly always occur in elderly women after menopause (as well as in a smaller number of older men). And that age group has been the focus of prevention and treatment efforts.

Now a controversial report suggests the disease often begins in younger women who have no outward sign of bone problems. The findings, reported last week in the New England Journal of Medicine by a team from the University of British Columbia, raise the possibility that more than half of all healthy women in their 30s and 40s could be suffering from bone damage as a result of subtle, undetected disturbances in their menstrual cycles. But some experts doubt the conclusions and call for follow-up trials before doctors change their approach to the disease.

Bone, like many tissues, is constantly being broken down and rebuilt. In younger women this balance is thought to be maintained, at least in part, by the hormone estrogen. The sharply reduced production of estrogen after menopause, many researchers believe, upsets that balance, triggering a gradual loss of bone tissue. In about one-quarter of women, this deterioration eventually results in the porous, brittle bones characteristic of osteoporosis.

In the new study, however, the researchers were not examining older women. Instead, they were trying to find out why one group of young women -- marathon runners -- seemed to be peculiarly predisposed to osteoporosis. The researchers theorized that disruptions in the runners' menstrual cycles might be at fault. But to their surprise, when they compared the marathoners with women who ran for recreation and others who engaged in no special physical activity, the researchers found that menstrual disturbances were common in all three groups.

In fact, almost 30% of all cycles experienced by the 66 women over a 12- month span were in some way disrupted. The upset was caused either by a failure to ovulate (or produce an egg) or by a shortened "luteal phase," a critical stage of the menstrual cycle during which the hormone progesterone is produced. More important the researchers found that these disturbances were directly related to dramatic bone loss: the 20% who missed ovulation at least once, for example, suffered as much as a 4% reduction in bone density in one year.

How might menstrual problems hurt bones? Lead researcher Jerilynn Prior believes that reduced levels of the hormone progesterone -- which was suppressed in women with cycle disruptions -- may explain the damage. Some studies have indicated that this hormone helps with bone formation. Prior is not certain what causes the menstrual disturbances. The most likely candidate, she says, is stress.

But other experts are skeptical. Dr. Charles Chesnut III, director of the Osteoporosis Research Center at the University of Washington, points out that it would be premature to draw major conclusions from such a short-term study. Longer trials are needed to show whether the bone damage is permanent. Besides, several experts contend, if such dramatic bone loss were in fact occurring in so many younger women, then it would have been obvious to doctors before now. If the study was exactly right, argues Chesnut, "most women would be entering menopause with no skeletons."

Yet even if Prior's research overestimates the degree of bone damage in young women, the study is intriguing evidence that osteoporosis can at least get started at an early age. If that is confirmed, the information suggests that preventive steps -- perhaps progesterone therapy -- may help some women ward off the disease before it becomes crippling.