We measured fasting serum levels of
type I procollagen C-terminal propeptide (
PICP),
insulin-like growth factor-I (
IGF-I), and IGF binding protein-3 (IGFBP-3) in obese children and adolescents (obese subjects [OS]) to evaluate their relationship to growth, gender, pubertal stage, and weight excess (WE). The influence of
insulin,
growth hormone (GH), and
weight loss was also studied. The study population consisted of 244 OS and 236 normal-weight subjects (NWS) matched for age, gender, and pubertal stage. At stage I, OS had a higher standard deviation score (SDS) for height than NWS of both genders. During the prepubertal phase, growth velocity (GV) was greater in OS than in NWS of both genders, but it was lower in female OS at stage II and male OS at stage III.
PICP increased in puberty, with a more rapid decrease later in female OS and NWS; prepubertal values were higher in OS but were reduced at pubertal stage IV to V in comparison to NWS. Stepwise multiple regression analysis demonstrated that GV was the only anthropological variable correlating with
PICP.
IGF-I serum values increased significantly in puberty and were higher in OS than in NWS at stage I for both genders.
IGFBP-3 values of OS exceeded those of NWS at stages I to III in males and I to II in females. No difference was observed for males versus females in each group, nor was any difference observed for the
IGF-I/
IGFBP-3 molar ratio between the two groups. Using stepwise analysis, a positive correlation between
IGF-1 and
IGFBP-3 was observed in prepubertal but not in pubertal NWS. Fasting
insulin values correlated with
IGFBP-3 in OS, accounting for 24.8% of the variation in prepubertal subjects and 17.1% in pubertal subjects. No such correlation was observed in NWS. In prepubertal NWS,
PICP and SDS of body mass index (BMI) correlated with
IGF-I, accounting for 12.9% of the variation, and SDS of BMI correlated with
IGFBP-3, explaining 27.8% of the variation. In prepubertal OS, no such correlations could be observed, but
PICP and SDS of BMI accounted for 14.3% of the variation in the
IGF-I/
IGFBP-3 molar ratio. A significant reduction of
IGFBP-3 and an increase of the
IGF-I/
IGFBP-3 molar ratio were detected after
weight loss in 40 OS. In conclusion, we demonstrated that
IGF-I and
IGFBP-3 are influenced by age, gender, sexual development, and nutritional status. Also, an influence of
insulin on
IGFBP-3 serum levels was observed in OS. The relations of
IGF-I to
PICP in NWS and of the
IGF-I/
IGFBP-3 molar ratio to
PICP in OS support the concept of
IGF-I influence on skeletal growth. The increased
IGFBP-3 serum values in OS suggest a possible role in controlling the growth stimulus induced by nutritional status.