Insulin-like growth factors and bone mineral density in African American and white girls

Objectives: African American children have greater bone mineral density (BMD) and bone mineral content (BMC) than white children. We examined the hypothesis that differences in insulin-like growth factors (IGFs) are important determinants of BMD during childhood. Methods: We measured IGFs and IGF binding proteins in 59 African American and 59 white girls matched for age, body mass index, socioeconomic status, and pubertal stage. BMD and BMC were determined by dual emission x-ray absorptiometry, Results: African American girls had greater total BMD (P < .001), BMC (P < .01), total IGF-1 (P < .001),and free IGF-1 (P < .01) than white girls. IGFBP-1, IGFBP-2, and IGFBP-3 were similar in both groups or lower in African Americans. IGF-1 was positively correlated with IGF-2 in white girls (P = .012) but was negatively correlated with IGF-2 in African Americans (P = .015). IGF-1 and free IGF-1 were positively correlated with BMD/BMC. Multiple regression analyses showed 80% of the variance in BMC could be accounted for by the use of body weight, height, and IGF-1 in the model. When IGF-1 was included as a factor, race did not add to the model's predictive power. Conclusion: IGF-1 and free IGF-1 are greater in African American than in white girls and may contribute to the greater BMD of African Americans.