Defining the end of puberty in boys: INSL3 and the acute determinants of adult Leydig-cell functional capacity.
Level 3 - non-randomized controlled study
Longitudinal prospective cohort study tracking endocrine development over time
PubMed 40496564 · doi:10.3389/fendo.2025.1574760
What was done
Analyzed circulating insulin-like peptide 3 (INSL3)—a constitutive biomarker reflecting the total population and differentiation status of testicular Leydig cells—in young men from the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. The authors evaluated INSL3 trajectories across late adolescence and young adulthood (including measurements at 17 and 24 years) to estimate when adult Leydig-cell capacity is established and assessed associations with contemporary body mass index (BMI), smoking status, and inflammatory markers.
What was found
At 17 years, mean INSL3 was not yet maximal and exhibited high variance. Maximal INSL3 concentration (peak puberty) was calculated to occur at approximately 22 years of age. By 24 years, circulating INSL3 stabilized into its final adult status, showing a slight decreasing trend with age. Contemporary BMI and smoking status contributed to INSL3 concentrations, while inflammatory parameters did not. The major source of variance in young men was already established at 17 years. The abstract reports no specific numerical concentrations, effect sizes, or participant counts.
Why it matters
This study indicates that male pubertal development and full adult Leydig-cell capacity culminate around 22 years of age, demonstrating that the biological capacity for adult testosterone production is largely determined by early-life factors established prior to age 17.
Limits
The abstract does not report sample size (n), absolute numerical values, effect sizes, or confidence intervals. Findings are derived from a single regional UK birth cohort (ALSPAC), and the specific early-life causal factors operating before age 17 were not resolved in this report.
Cited by
- supports In men, testosterone levels continue to increase through their teenage years and into their 20s after puberty has ended.