Higher Peak Height Velocity in Early Maturing Girls Depends on Insulin rather than Fat Mass or IGF-I.

OBJECTIVE Age at pubertal onset has decreased over the recent decades. Early maturing girls have longer puberty duration, and higher peak height velocity (PHV) than late maturing girls. To what extent this is generated by increased insulin-like growth factor-I (IGF-I), fat mass or fasting insulin levels is currently unknown. DESIGN, SETTING, PARTICIPANTS A population-based study - part of the COPENHAGEN puberty study - longitudinal part. Eighty-one girls evaluated biannually for a median of 10 (2-15) visits for a total of 815 evaluations. METHODS Pubertal staging, anthropometric measures, PHV, skin fold thickness (SFT) and IGF-I and fasting Insulin levels were measured. RESULTS Early maturing girls achieved similar final height compared to late maturing girls (166.1 vs 167.1 cm, p = 0.36). Early pubertal onset was associated with significantly greater PHV (8.7 vs. 7.4 cm/year, p < 0.001) and a longer puberty duration (age at onset of breast development to age at PHV [1.8 vs. 1.1 years, p < 0.001]) compared with late maturation. After correcting for age at pubertal onset, neither BMI, SFT nor IGF-I levels differed between early versus late maturing girls. By contrast, fasting insulin levels were significantly higher in early compared with late maturing girls 1.5, 2.0 and 3.0 years after pubertal onset (all p = 0.039). CONCLUSION Growth velocity was higher and more prolonged in early compared with late maturing girls and associated with higher insulin levels. Thus, the higher insulin levels may compensate for the shorter total growth period by intensifying the pubertal growth period.