Growth hormone secretion and bone mineral density in prepubertal black and white boys

Racial differences in bone mineral density (BMD) appear to account in part for racial differences in the incidence of osteoporosis and fractures. We previously reported that the greater BMD in adult blacks compared with whites is associated with a higher serum 17 beta-estradiol and greater secretion of growth hormone (GH) in men but not women. To determine whether these racial differences occur in prepubertal boys, we measured spontaneous overnight GH secretion, serum testosterone, 17 beta-estradiol, IGF-I, and IGFBP3, IGF-I/ IGFBP3 ratio, BMD of the total body, forearm, lumbar spine, trochanter, and femoral neck, and lean body mass and body fat in 14 healthy black and 16 white boys ages 6-7 years. Measurements of GH were obtained at 20-minute intervals for 12 hours. Results were analyzed by deconvolution and are expressed as mean +/- SE. Whereas BMD of the hip (0.755 +/- 0.020 vs 0.663 +/- 0.021 g/cm(2), P = 0.0037), trochanter (0.617 +/- 0.014 vs 0.552 +/- 0.018 g/cm(2), P = 0.0102) and femoral neck (0.710+/-0.018 vs 0.6381 +/- 0.021 g/cm(2), P = 0.0157) were significantly greater in black compared with white boys, BMD of the total body (0.768 +/- 0.010 vs 0.741 +/- 0.012 g/cm(2), NS), forearm (0.405 +/- 0.010 vs 0.380 +/- 0.008 g/cm(2), NS), and lumbar spine (0.612 +/- 0.013 vs 0.609 +/- 0.021 g/cm(2), NS) was not different in the two groups. Stepwise regression analysis showed significant correlations between BMD and race at each skeletal site except the lumbar spine and trochanter. Deconvolution analysis revealed no racial difference in any of the GH measurements. Whereas serum testosterone, serum 17 beta-estradiol, and serum IGF-I were not different, serum IGFBP-3 was higher and the molar ratio of serum IGF-l/IGFBP-3 was lower in white than in black males. In summary, prepubertal BMD is higher in black than in white males at the hip, trochanter, and femoral neck, and the racial difference does not result from differences in secretion of GH.