Calcitropic Hormone Levels in Polynesians: Evidence against Their Role in Interracial Differences in Bone Mass*

Abstract

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.