Early menopause, number of reproductive years, and bone mineral density in postmenopausal women.

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Abstract
Previous studies have reported positive associations of age at menopause with bone density and inverse associations of age at menarche with bone density. This study examined the relationships of early age at menopause and number of reproductive years (defined as age at menopause minus age at menarche) with bone density in postmenopausal women. The subjects were 555 women aged 60 to 89 years who had had either natural menopause (n = 391) or hysterectomy with bilateral oophorectomy (n = 164). Bone density was measured at the ultradistal wrist, midshaft radius, lumbar spine, and hip. Women who had had early menopause and those with the fewest reproductive years had significantly lower bone density at all sites. After adjustment for covariates, both age at menopause and number of reproductive years had significant positive associations with bone density at every site, and total number of reproductive years explained more of the variance in bone mineral density than did either age at menarche or age at menopause. Elderly women reporting early menopause or fewer reproductive years have more osteoporosis. The number of reproductive years may be more helpful than age at menopause in identifying women at increased risk of osteoporosis.