Bone mineral density in older non-Hispanic Caucasian and Mexican-American women: relationship to lean and fat mass

Primary objective: The prevalence of osteoporotic fracture is higher in non -Hispanic Caucasian (NI-IC) than Mexican-American (MA) women in the USA. Th e present study examined bone mineral density (BMD) in these two ethnic gro ups and the association between BMD and body composition. Research design: Cross-sectional, Subjects: Sixty-two NHC and 54 MA women, aged 60 86 years, with a body mass index (kg m(-2)) of < 30. Methods: BMD (g cm(-2)) of the spine (L2-4), hip (femoral neck, trochanter, Ward's triangle) and whole body was determined by dual-energy X-ray absorp tiometry (DXA). Bone mineral-free lean mass (LM) and fat mass (FM) and seve ral ratios of body fat distribution were also assessed by DXA. Results: There was no difference in age (NHC, 69.5 +/- 0.7; MA 69.5 +/- 0.9 years; mean +/- SEM) or body mass, but MA women were shorter with a higher truncal adiposity (p < 0.001). There was no significant difference in BMD between groups, however, adjusting for height resulted in higher hip and wh ole body BMD in MA women (p< 0.01). When volumetric bone density was calcul ated (bone mineral apparent density; BMAD, g cm(-3)), a trend for higher va lues in MA women was observed at the femoral neck (p = 0.018). LM contribut ed independently to BMD at the spine and hip in NHC women, with FM also con tributing at the femoral neck. In MA women, LM was an independent contribut or to lumbar spine and trochanter BMD, and both LM and FM contributed to wh ole body BMD, However, the effects of LM and FM were removed in both groups when BMD was adjusted for body or bone size, the only exception being at t he trochanter in NHC women. Conclusions: These results indicate that MA women have higher bone density at the proximal femur than NHC women, which may partially account for their lower rate of hip fracture. Further, differences in bone density between t he two ethnic groups do not appear to be dependent on soft-tissue compositi on.