Calcium, vitamin D-endocrine system, and parathyroid hormone in black and white males.

The serum and urinary calcium, 25-hydroxyvitamin D (25OHD), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), and parathyroid hormone (PTH) were studied in healthy black and white males living in Belgium, and the results were compared to data in blacks of similar age living in Zaïre. Dietary calcium and vitamin D were estimated in a sub-sample of blacks and whites examined in Belgium. Compared to whites (9.51 +/- 0.28 mg%) serum calcium was somewhat lower in blacks (9.26 +/- 0.27 mg% in Belgium; 9.19 +/- 0.48 mg% in Zaïre). The 24 hour urinary calcium excretion averaged 215.0 +/- 16.7 mg% in whites and was higher (P less than 0.05 or less) than in blacks (115 +/- 71 mg% in Belgium; 36 +/- 33 mg% in Zaïre). The serum 25OHD levels were similar in whites and blacks evaluated in Zaïre, both being higher (P less than 0.05 or less) than in blacks living in Belgium. In the latter blacks, an inverse correlation was observed between the 25OHD level and the duration of the stay in a temperate climate. Parathyroid hormone levels were slightly higher in blacks living in Belgium than in the other two groups of subjects. The serum levels of 1,25(OH)2D3 and human vitamin D-binding protein were similar in the three groups of subjects. Dietary calcium averaged 541 +/- 152 mg/day in blacks and was significantly (P less than 0.001) less than in whites (1,203 +/- 508 mg/day), whereas no significant difference was observed in dietary vitamin D intake between blacks and whites. It is concluded that calcium intake is low in blacks but stimulation of parathyroid hormone and 1,25(OH)2D3 required to achieve normocalcemia does not occur.