Childhood BMI is inversely associated with pubertal timing in normal-weight but not overweight boys

Abstract

BackgroundAn inverse association between childhood body mass index (BMI; in kg/m2) and pubertal timing is well established for girls. Among boys, studies are scarce and the results inconclusive.ObjectiveWe aimed to determine the association between childhood BMI and age at peak height velocity (PHV) in boys.DesignWe collected height and weight measurements between 6.5 and 22 y of age for boys born 1945–1961 (original cohort; n = 31,971; mean ± SD childhood BMI: 15.74 ± 1.41; age at PHV: 14.06 ± 1.11 y) and 1981–1996 (replication cohort; n = 1465; childhood BMI: 16.47 ± 2.06; age at PHV: 13.71 ± 1.08 y) attending schools in Gothenburg, Sweden, and examined at mandatory military conscription. Age at PHV was obtained from curve-fitting of measured heights with the use of a modified Infancy-Childhood-Puberty model.ResultsIn the original cohort, childhood BMI was inversely associated with age at PHV (P < 0.001) and a significant quadratic term for childhood BMI (P < 0.001) indicated the nonlinearity of this association. Via piecewise linear regression, we identified a threshold for the association at a childhood BMI of 18.42. A significant inverse association was observed below (β: −0.17 y/BMI unit; 95% CI: −0.18, −0.16 y/BMI unit) but not above (β: 0.02 y/BMI unit; 95% CI: −0.03, 0.06 y/BMI unit) this childhood BMI threshold. For every unit increase in childhood BMI, age at PHV was ∼2 mo earlier up to the childhood BMI threshold. Similar results were observed in the replication cohort, demonstrating a significant inverse association below (β: −0.16; 95% CI: −0.21, −0.11) but not above (β: −0.03; 95% CI: −0.11, 0.05) the childhood BMI threshold. The identified threshold was close to the cutoffs for overweight at 8 y of age, and childhood BMI was inversely associated with age at PHV below but not above the overweight cutoffs.ConclusionsThe present findings establish an inverse association between childhood BMI and pubertal timing in normal-weight but not overweight boys.

Early puberty and risk for type 2 diabetes in men

“…We used a modified Infancy-Childhood-Puberty model [20] to calculate age at peak height velocity (PHV), an objective assessment of pubertal timing, in men. Using these data, we have recently demonstrated an inverse association between prepubertal BMI at age 8 and age at PHV [19], and we also observed a clear secular trend towards earlier age at PHV in males from the 1940s up to the present [21].…”

“…Age at PHV is the age at the time of the maximum growth spurt, which occurs approximately 2 years after pubertal onset in boys [32]. Using age at PHV we recently reported a secular trend for pubertal timing from the 1940s onwards [21] and we have also demonstrated an inverse association between prepubertal childhood BMI and age at PHV [19]. In the current study we demonstrate that early age at pubertal timing is associated with increased risk of adult type 2 diabetes, independent of childhood BMI, in Swedish men.…”

“…Retrospective studies of male puberty are limited by the lack of easily available pubertal indicators, therefore, less is known regarding the determinants and the consequences of male pubertal timing. We have collected retrospective growth data, calculated age at PHV according to a modified infancy-childhood-puberty model [20] and used it as an objective assessment of pubertal timing in boys, as previously described [19,21,25]. Age at PHV is the age at the time of the maximum growth spurt, which occurs approximately 2 years after pubertal onset in boys [32].…”

“…The following subjects were excluded before study start: (1) subjects with an incomplete PIN; (2) subjects lacking childhood BMI, young adult BMI or age at PHV; (3) To adequately calculate age at PHV in an unbiased manner, height measurements before, during and after the pubertal period are required. We calculated age at PHVaccording to the infancychildhood-puberty (ICP) model [20] that we had further developed (using R [24]) as previously described [19,25]. Age at PHV was defined as age at the maximum growth velocity during puberty and was estimated by the curve-fitting program.…”

“…Age at voice breaking when reported by recall in adult life has not been validated [18]. Importantly, the analyses in the UK Biobank study could not be adjusted for prepubertal BMI, which is known to influence pubertal timing in men [19]. Therefore, the association between pubertal timing and type 2 diabetes, independent of prepubertal BMI, is unknown in men [5].…”