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There are substantial inter-racial differences in hip fracture incidence. Studies in several different ethnic groups have suggested that differences in the length of the femoral neck may contribute to these. The present study assesses femoral neck and hip axis lengths in three ethnic groups in which it has not been documented previously (Chinese, Indians and Polynesians) and compares these values with those in Europeans. Lengths were measured from dual-energy X-ray absorptiometry scans of the proximal femur in normal premenopausal women (n = 225). The Polynesian (1.65 m) and European (1.64 m) women were significantly taller than the two Asian groups (mean height in each, 1.58 m). There were also differences in mean body weight, the Polynesians being the heaviest (76 kg) and the Chinese the lightest (53 kg). Femoral neck lengths were (mean +/- SD) Chinese 61.5 +/- 4.4 mm, Indian 61.5 +/- 5.1 mm, Polynesian 68.2 +/- 4.3 mm and Europeans 66.0 +/- 4.8 mm. Hip axis lengths were Chinese 98.0 +/- 5.6 mm, Indian 94.5 +/- 5.2 mm, Polynesian 106.4 +/- 5.3 mm and European 102.3 +/- 5.3 mm. Each of the other groups were significantly different from the Europeans for both variables and, in general, this remained so after height adjustment. These data suggest that shorter femoral necks are common to the major Asian racial groups. However, in contrast to all other ethnic groups studied, Polynesians have longer femoral necks than Europeans and their low incidence of hip fracture is not explicable, therefore, in terms of their femoral neck length. This suggests that either higher bone density or other more subtle differences in proximal femoral geometry must account for the low hip fracture incidence in Polynesians.

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/cm2) were similar, but significantly less, at all sites, than those of European women (p < or = 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Blacks are known to have a higher bone mass than whites and have recently been found to have significantly different levels of calcitropic hormones and other biochemical indices of calcium metabolism. To assess the possible significance of these biochemical differences to interracial differences in bone mass, we have undertaken an assessment of indices of calcium metabolism in Polynesian subjects, since they also have a higher bone mass than whites. Serum concentrations of 25-hydroxyvitamin D were slightly lower in Polynesians than in whites (65 +/- 5 vs. 95 +/- 10 nmol/L; P less than 0.02), but there were no differences between the groups in serum levels of calcium (total and ionized), phosphate, magnesium, 1,25-dihydroxyvitamin D, PTH, calcitonin, alkaline phosphatase activity, and bone gla-protein. Furthermore, urinary excretion of hydroxyproline, calcium, phosphate, magnesium, sodium, and potassium and the tubular maximum for the reabsorption of phosphate were not different between whites and Polynesians. Intestinal strontium absorption was similar in the two groups. In contrast, distal forearm bone mineral content was higher in Polynesians (P less than 0.01) and midupper arm muscle area was also increased in this group (P less than 0.005). It is concluded that the higher bone mass of Polynesians cannot be attributed to alterations in the basal levels of calcitropic hormones, but may be related to their greater muscle mass. It is probable that the previously observed black-white differences in the vitamin D endocrine system are secondary to the effects of skin color on vitamin D synthesis and are not contributory to the lower bone mass of whites.