Abstract and Introduction
Context: Pubertal timing in boys is associated with body mass index (BMI). Studies consistently report an inverse correlation of BMI and pubertal timing within the normal BMI range. However, observations in obese boys are conflicting with different studies reporting either early or delayed pubertal onset in obese boys.
Objective: We aimed to assess the association of male pubertal timing with age-specific BMI (zBMI) in obese boys.
Design, Setting, and Participants: A total of 218 obese boys (zBMI > +2SD, with a median age at baseline of 10.8 years (range 4.2–17.0), were recruited as part of a prospective outpatient childhood obesity intervention program at Nordsjællands Hospital, Hillerød, Denmark, between 2009 and 2017. Serving as controls, we included 660 healthy boys participating in the population-based COPENHAGEN Puberty Study (-2SD < zBMI ≤ +2SD, 2006–2014). Subanalyses were performed on overweight controls (+1SD < zBMI ≤ +2SD). The clinical assessment of pubertal development by Tanner staging, including testis volume using a Prader's orchidometer, was performed by trained physicians. The timing of pubertal milestones was estimated by probit analyses.
Main Outcome Measures: Timing of testicular volume ≥ 4 mL, genital stage ≥ 2, and pubarche.
Results: The mean (95% confidence interval [CI]) age of onset of pubertal event in obese boys was as follows: testicular volume ≥ 4 mL, 11.3 years (11.0–11.6); genital stage ≥ 2, 11.6 yrs (11.3–11.9); and pubarche, 11.9 years (11.5–12.3). Testicular volume ≥ 4 mL occurred significantly earlier in obese boys compared to controls (-2SD < zBMI ≤ +2SD) (P = 0.01). We did not observe significant differences for either the timing of pubarche nor the genital stage ≥ 2 (P = 0.06 and P = 0.94, respectively).
Conclusions: We demonstrate that testicular enlargement in obese boys occurs significantly earlier compared to a population-based normal-weight reference cohort.
The relation between obesity and male pubertal timing is an ongoing topic of debate. In contrast to consistent reports of a strong negative association of body mass index (BMI) with female puberty timing across the entire BMI spectrum, conflicting reports concerning the association of BMI with male puberty timing exist. Many studies report an inverse linear relation between BMI and male pubertal onset.[2–5] However, some studies report a delayed onset in obese boys compared to overweight boys pointing to a non-linear, J-shaped association.[6,7] While BMI is usually increasing during puberty due to changes in body composition, age-specific BMI (zBMI) remains relatively stable throughout pubertal transition. Age-specific body mass index scores represent a proxy of body fat mass and exhibits strong correlations with other readouts of body fat mass, for example, skin fold measurement or body fat assessment by dual energy x-ray absorptiometry. The strong association of pubertal timing and metabolic factors is well known. Recent large-scale genetic studies underlined a significant negative genetic correlation between BMI and male pubertal timing[10,11] and further identified a causal effect of higher BMI on earlier pubertal timing in boys. However, whether this effect is preserved at the far end of the BMI spectrum remains debated. Given the conflicting reports on the association of obesity with male pubertal timing, we compared pubertal timing in obese children to population-based controls.
J Clin Endocrinol Metab. 2020;105(4) © 2020 Endocrine Society