Serum concentrations of insulin, insulin-like growth factor, and insulin-like growth factor binding proteins are different between white and African American girls

Objectives: To determine whether serum insulin-like growth factor (IGF)-I a nd IGF binding protein (IGFBP) concentrations are different between African American and white girls. Study design: Serum glucose and hormone concentrations were measured in blo od samples collected after a 12-hour fast from 79 white and 57 African Amer ican healthy girls between 9 and 17 years of age. Tanner stages of pubic ha ir development were evaluated by physical examination, and body composition by dual energy x-ray absorptiometry. Results: The African American girls were older and sexually more mature and had higher fat mass, higher serum insulin and free IGF-I concentrations, h igher serum free IGF-T to total IGF-I ratio, but lower serum IGFBP-I sexual maturation and fat mass, the serum concentrations of total IGF-I, bound IG F-I, and IGFBP-3 in the white girls became significantly higher than those in the African American girls. The higher concentrations of total IGF-I in the white girls were due to a proportional increase in the concentrations o f bound IGF-I that coincided with a similar increase in serum IGFBP-3 conce ntrations. Conclusions: Higher serum insulin concentrations in the African American gi rls are associated with lower serum IGFBP-I concentrations and increased bi oavailability of free IGF-I, which may contribute to their accelerated grow th compared with their white counterparts.