Bone mineral density and the risk of incident nonspinal fractures in black and white women.
BACKGROUND
Black women have a lower rate of fracture than white women, but whether bone mineral density (BMD) predicts fracture risk as well in black women as it does in white women is not established.


OBJECTIVE
To examine the association between BMD and incident nonspinal fractures in older black and white women.


METHODS
Prospective cohort study of baseline data collected from 1986 through 1990 (7334 white women aged 67-99 years) and from 1996 through 1998 (636 black women aged 65-94 years) at 4 US clinical centers in the Study of Osteoporotic Fractures; mean (SD) follow-up of 6.1 (1.5) years until October 1, 2004.


METHODS
Incident nonspinal fractures were confirmed by radiograpic report. Total hip and femoral neck BMD and bone mineral content were measured by dual energy x-ray absorptiometry.


RESULTS
A total of 58 black women had a combined total of 61 fractures and 1606 white women had a combined total of 1712 fractures. In age-adjusted proportional hazard models, a 1-SD decrease in femoral neck BMD was associated with a 37% increased risk of fracture in black women (relative risk [RR], 1.37; 95% confidence interval [CI], 1.08-1.74) and a 49% increase in fracture in white women (RR, 1.49; 95% CI, 1.40-1.58). Adjustment for body weight and other risk factors for fracture weakened the association between BMD and fracture, especially among black women (multivariable adjusted RR per 1-SD decrease in femoral neck BMD for black vs white women: RR, 1.20 [95% CI, 0.93-1.55] vs RR, 1.42 [95% CI, 1.32-1.52]). The absolute incidence of fracture across the pooled BMD distribution was 30% to 40% lower among black women at every BMD tertile. The lower risk of fracture among black compared with white women was independent of BMD and other risk factors (RR, 0.48; 95% CI, 0.36-0.64).


CONCLUSIONS
Decreased total hip and femoral neck BMD is associated with an increased risk of fracture in both older black and white women, but this relationship was largely explained by other risk factors in black women. Black women have a lower fracture risk than white women at every level of BMD. Race-specific normative databases may be appropriate for the densitometric definition of osteoporosis.
Cauley
Jane A
JA
Department of Epidemiology, University of Pittsburgh, Pittsburgh, Pa 15261, USA. jcauley@pitt.edu
Lui
Li-Yung
LY
Ensrud
Kristine E
KE
Zmuda
Joseph M
JM
Stone
Katie L
KL
Hochberg
Marc C
MC
Cummings
Steven R
SR
D000368:Aged; D000369:Aged, 80 and over; D044383:Black People / Q000706:statistics & numerical data*; D015519:Bone Density; D005260:Female; D050723:Fractures, Bone / Q000453:epidemiology / Q000208:ethnology*; D006801:Humans; D010024:Osteoporosis / Q000208:ethnology*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012306:Risk; D014481:United States / Q000453:epidemiology; D044465:White People / Q000706:statistics & numerical data*; D001741:Black or African American