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 do not 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% 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.
The work, conducted at the University of British Columbia in Vancouver, was published last week in the New England Journal of Medicine.