THE EFFECT OF POSTMENOPAUSAL ESTROGEN THERAPY ON BONE-DENSITY IN ELDERLY WOMEN

Background. Estrogen therapy prevents bone loss in postmenopausal wome n who take it early in the postmenopausal period. The risk of fracture is highest much later in life, however. We studied whether bone mass in elderly women was affected by earlier estrogen use and how long wom en needed to take estrogen for it to have a beneficial effect on bone density later in life. Methods. In 1988 and 1989, we measured bone min eral density at the femur, spine, shaft of the radius, and ultradistal radius in 670 white women in the Framingham Study cohort (mean age, 7 6 years; range, 68 to 96). These women had been followed prospectively through menopause and had been asked repeatedly about estrogen therap y. After excluding women who began taking estrogen after a fracture, w e investigated whether postmenopausal estrogen therapy affected bone d ensity; in these analyses we adjusted for age, weight, height, cigaret te smoking, physical activity, and age at menopause. Results. A total of 212 women (31.6 percent) had received estrogen therapy (mean estima ted duration of treatment, 5 years). Only women who had taken estrogen for 7 to 9 years or for 10 or more years had significantly higher bon e mineral density than women who had not taken estrogen (7 to 9 years of treatment, P<0.05 at sites in the femur and the spine; greater-than -or-equal-to 10 years, P<0.05 at all sites except the spine). In the w omen less than 75 years of age who had taken estrogen for seven or mor e years, the bone density was, averaging all sites, 11.2 percent great er than in women who had never received estrogen. Among women 75 years of age and older in whom the duration of therapy was comparable, bone density was only 3.2 percent higher than in women who had never taken estrogen. Conclusions. For long-term preservation of bone mineral den sity, women should take estrogen for at least seven years after menopa use. Even this duration of therapy may have little residual effect on bone density among women 75 years of age and older, who have the highe st risk of fracture.