Sources of interracial variation in bone mineral density

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Abstract
Many studies have demonstrated significant differences in bone mineral density between various racial groups. Although it has been suggested that differences in body weight contribute to such interracial variation, the artifactual effect of the skeletal size inherent in projectional absorptiometry methods has been largely ignored. We have measured bone mineral density by dual‐energy X‐ray absorptiometry in the lumbar spine and at three femoral sites in 200 premenopausal women of Chinese, Indian, European, or Polynesian origin (50 of similar mean age in each group). In the Chinese and Indian women the measured bone mineral density measurements (g/cm) were similar, but significantly less, at all sites, than those of European women (p ≤ 0.005). The European women were, however, significantly taller than both the Chinese and Indian women (p < 0.0001), and when the scale artifact of absorptiometry was removed by dividing the measured bone mineral density either by the height of the subject, or by the square root of the area over which the X‐ray beam was projected, then the differences in mean bone mineral density between the Chinese, Indian, and European women were almost completely eliminated. The Polynesian women were significantly more obese (as judged from mean body mass index) than all the other groups (p < 0.0001) and had significantly greater bone mineral density at all sites than all the other groups both before (p < 0.0001) and after (p < 0.0001) correcting for the scale artifact. Analysis of covariance suggested that 10–40% of the remaining increase in bone density could be accounted for by their greater obesity, the balance representing a true interracial difference. This effect was most obvious in the lumbar spine and least evident at the femoral sites. We conclude that there is a true interracial difference in bone mineral density between Polynesians and the other races studied, and that this is increased further by the greater body weight of Polynesians. The differences between Europeans and Asians are substantially attributable to a measurement artifact arising from the smaller skeletal dimensions of Asians. This needs to be borne in mind by clinicians assessing bone density in Asian patients.
Funding Information
  • Health Research Council of New Zealand, the New Zealand Lottery Board
  • Arthritis and Rheumatism Foundation of New Zealand

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