Longitudinal study of changes in hip bone mineral density in Caucasian and African-American women

OBJECTIVES: To determine whether changes in hip bone mineral density (BMD) differ in Caucasian and African American women. DESIGN: Longitudinal study of changes in hip BMD. SETTING: Four U.S. clinical centers. PARTICIPANTS: Six thousand seven Caucasian (mean age 73) and 482 African-American (mean age 75) women enrolled in the Study of Osteoporotic Fractures. MEASUREMENTS: Total hip and femoral neck BMD were measured an average of 3.5 years apart (Caucasian) and 2.0 years apart (African American). Annual absolute and percentage changes in BMD and bone mineral apparent density (BMAD) were calculated. RESULTS: The multivariate adjusted annual percentage change in BMD was greater in Caucasian than African-American women at the total hip (-0.574%/y vs -0.334%/y) and femoral neck (-0.515%/y vs -0.203%/y) (both, P<.001). Similar findings were observed for BMAD. The average annualized rate of BMD loss was twice as high in women aged 75 and older as in women younger than 75 in both ethnic groups. The annual percentage loss in femoral neck BMD in nonusers versus hormone therapy users was (-0.57% vs -0.22%) in Caucasians and (-0.35% vs 0.64%) in African Americans (interaction P=.03). CONCLUSION: The average rate of hip BMD loss is approximately twice as great in Caucasian as African-American women and increases with age in both groups. The hormonal and biochemical factors that contribute to ethnic differences and the increase in bone loss with advancing age need to be identified.