African American (AA) and Caucasian (C) children have many differences in body composition, including greater bone mineral density in AA. In adults, conflicting results of growth hormone secretion have been described in AA and C males and females. However, the molar ratio of IGF-1/IGF BP3 appears greater in AA than C. To examine the hypothesis that differences in IGF's may be an important determinant of racial differences in body composition during childhood, when differences in bone mineral density first become apparent, we measured IGF's and related binding proteins in 60 normal AA (N=34, age 8.6± 1.2 y) and C (N=35, age 8.6 ± 1.2 y) girls, who were matched for weight, body mass index, socioeconomic status and for Tanner breast stage, and related them to measures of body composition as determined by dual emission xray absorptiometry (DXA). AA girls had a significantly lower waist:thigh ratio (1.52 ± 0.08 vs 1.58 ± 0.09, p < 0.001), and significantly greater total body bone mineral density (0.831 ± 0.054 vs.792 ± 0.43 g/cm2, p < 0.005), IGF-1 (278.5 ± 139.7 vs 189.2 ± 85.4 ng/mL, p < 0.001) and free IGF-1 (9.57 ± 5.4 vs 4.0 ± 2.0 ng/mL, p < 0.01) than C girls. IGF-BP3 (3.0 ± 0.7 vs 3.3 ± 1.1), IGF-2 (256.7 ± 50.1 vs 307.7 ± 74.9), and GHBP (1279.1 ± 410.9 vs 1204.3 ± 540.4 pmol/L) were all similar in AA and C. IGF-1 and free IGF-1 concentrations were positively correlated with bone mineral content in both AA and C.

We conclude that both IGF-1 and free IGF-1 are greater in AA than C prepubertal and early pubertal girls. Greater IGF-1 production may be one of the factors contributing to the greater bone mineral density and other body composition differences found in AA and C girls.