Serum levels of insulin-like growth factor (IGF)-I, free IGF-I, IGF binding protein (IGFBP)-1, IGFBP-3 and insulin in obese children

In simple obesity, spontaneous and stimulated growth hormone (GH) secretions are diminished. However, this diminished GH secretion does not result in decreased somatic growth in obese children. Although the increased insulin level, low insulin-like growth factor binding protein (IGFBP)-1 and the resulting increase of bioavailability of insulin-like growth factor I (IGF-I) have been suggested as being involved, the exact mechanism has not yet been established. We investigated serum IGF-I, free IGF-I, IGFBP-1, IGFBP-3 and insulin levels in 36 obese and 39 non-obese healthy children. Insulin and IGFBP-3 were significantly higher in the obese group than in the control group (p<0.05, p=0.001, respectively). IGF-I, free IGF-I, free IGF- I/IGF-I and IGFBP-1 levels in the obese children were not significantly different from those in the control group. A positive correlation was found between body mass index (BMI) and IGF-I in the obese children (r=0.30, p=0.05). IGFBP-3 levels correlated positively with IGF-I (r=0.44, p<0.005), and free IGF-I levels (r=0.37, p=0.05) in the obese children. A negative correlation was found between IGFBP-1 and insulin levels (r=0.30, p=0.05) in the obese children. We concluded that normal growth in obese children might be maintained through normal IGF-I and increased IGFBP-3 levels, which are stimulated by increased insulin levels or nutritional factors or by increased responsiveness to GH.