Longitudinal assessment of growth velocity in relation to pubertal timing, IGF-I, fasting insulin and fat mass in healthy boys.

Background: Age at puberty determines timing of pubertal growth spurt. Whether the intensity of the peri-pubertal growth velocity is also affected by pubertal timing in boys remains to be elucidated. Objective: To study changes in growth velocity in relation to pubertal timing, Insulin-like Growth Factor-I (IGF-I) and fasting insulin in healthy boys. Design, setting and participant: Longitudinal study with biannual assessment of testicular volume (TV), growth velocity, IGF-I and fasting insulin levels. Peak height velocity (PHV) was calculated. 105 boys (947 examinations) were included. Pubertal onset was available in 62 boys - the rest remained prepubertal throughout the study period or were in puberty at baseline. Results: Age at pubertal onset (TV > 3 ml) was negatively correlated with PHV (ρ = -0.48; p < 0.001). The early (age of onset < 33,3 percentile) tertile of maturing boys had significantly higher growth velocity (mean Δ 0.48 (0.14 - 0.82) cm/year; p < 0.006) than late maturing boys (> 66,7 percentile) over the 6 years peri-pubertal period. However, the late maturing boys remained significantly taller throughout the study (p < 0.05). IGF-I levels were similar between the 3 groups of boys. In all boys, the increase in growth velocity was associated with a larger increase in IGF-I (p < 0.001) during the first 2 years of puberty. Conclusion: Early maturation was associated with increased growth velocity and PHV in healthy boys. However, it was not sufficient to compensate for the shorter total growth period. IGF-I was positively associated with growth velocity.