Developmental changes in the relationship between IGF-I and body composition during puberty.

To examine the hypothesis that anthropometric measures and physical fitness influence circulating insulin-like growth factor-I (IGF-I) during puberty, we measured IGF-I, free IGF-I, IGFBP-1, and IGFBP-3 concentrations in 156 healthy girls (9-16 years old) characterized by aerobic capacity (VO2max), fat-free mass (FFM), percent fat mass and pubertal development. IGF-I, free IGF-I and IGFBP-3 increased with pubertal development while IGFBP-1 declined. Percent fat mass correlated inversely with IGFBP-1 (r = -0.57) and directly with insulin (r = 0.50), while VO2max correlated inversely with percent fat mass (r = -0.63), body mass index (BMI, r = -0.57), and FFM (r = -0.40). When subdivided by Tanner stage, IGF-I correlated directly with weight, height, BMI, and FFM in pre-pubertal girls, but these relationships all diminished or disappeared completely by late puberty. Inverse correlations between IGF-I and percent fat mass, and direct correlations between IGF-I and VO2max as observed previously in adults, were not seen until late puberty. These data suggest that in pre-pubertal and early pubertal girls, IGF-I concentrations in blood reflect overall somatic size. This relationship between IGF-I and body size diminishes with sexual maturation, while correlations between IGF-I and both fitness and fatness emerge.