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Study: Disrupted Ovulation Linked with Rapid Bone Loss

October 31, 1990

BOSTON (AP) _ Women who have outwardly normal menstrual periods may lose bone rapidly if they do not ovulate during every monthly cycle, a study concludes.

Lack of menstruation, such as occurs in women who exercise strenuously or don’t eat enough, has long been associated with weakened bones. But until now, experts assumed that women who menstruated regularly also produced hormones that kept their bones healthy.

The new research concludes that women who do not ovulate, or release an egg, every cycle lose 4 percent of the bone in their spines annually, even though they menstruate as usual.

The work also suggests that the hormone progesterone, as well as estrogen, is necessary for keeping women’s bones strong.

″There is far more variability in the normal menstrual cycle than anyone has realized, largely because it has not been looked for,″ said Dr. Jerilynn C. Prior, who directed the study.

She said stress and being too thin may cause disrupted ovulation, and women who regularly miss ovulation may need to take progesterone supplements to preserve their bones.

″It shows that some premenopausal women who have normal periods have ovulatory disturbances that are associated with bone loss. I don’t think people are aware of that,″ commented Dr. Deborah Riester of New England Medical Center in Boston.

The work, conducted at the University of British Columbia in Vancouver, was published in Thursday’s New England Journal of Medicine.

Women can have menstrual cycles that are regular in length and flow but still not ovulate. In such cycles, women produce normal amounts of estrogen but less than usual progesterone.

Some premenstrual symptoms may accompany ovulation. Prior said women can keep track of their ovulation by checking themselves for mild breast tenderness, a regular sign of the egg’s release.

In the study, doctors monitored the menstrual periods of 66 women who ranged from ages 21 to 42. One-third were runners preparing for a marathon, one-third were recreational runners and the rest were normally active non- runners.

The doctors expected to see more menstrual disruptions in the marathoners. Instead, they found that all the women had normal cycles 97 percent of the time, and ovulation disturbances occurred in 29 percent of their cycles. But the disturbances were no more common in the avid runners.

″These results suggest that the maintenance of peak bone density throughout adulthood requires normal ovarian production of both estrogen and progesterone,″ the researchers wrote. ″It is possible that a substantial percentage of premenopausal women who have apparently normal menstrual cycles may instead have asymptomatic ovulatory disturbances.″

However, since the study was conducted on a relatively small, carefully selected group, it is unclear whether ovulatory disturbances are anywhere near as common in the general population.

In an accompanying editorial, Drs. C. Conrad Johnston Jr. of Indiana University and Christopher Longscope of the University of Massachusetts called the observation important. However, they questioned whether women typically lose bone so quickly if their ovulation is disturbed.

″If such loss were to continue, these women would have very low spinal bone mass at the time of their menopause,″ they wrote, much lower than is typically seen.

They said the bone loss might not have continued beyond the one year of the study, or it might have been overestimated for technical reasons.

However, Prior said she believes a lifetime of irregular ovulation may be to blame for many of the fractures that occur in women soon after menopause.

Highly conditioned women athletes frequently stop menstruating entirely and are at high risk of losing bone and increasing their risk of fractures.

Riester, who is looking for treatments for these women, said she sees women in their 20s who have the bones of 50-year-olds.

″They think they are so healthy,″ she said, ″but they are going to run into a lot of problems with fractures.″

Riester said women who take birth control pills, which prevent ovulation, were not an issue in the study because the pills contain hormones. Therefore, women on the pill are not more susceptible to bone loss, Reister said.

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