Recent changes in pubertal timing in healthy Danish boys: associations with body mass index.

CONTEXT: In the 1990s, the American population-based study NHANES III renewed the focus on possible secular trends in male puberty. However, no conclusions could be made on pubertal onset due to the lack of compatible data.

OBJECTIVE: The aim of the study was to evaluate secular trends in pubertal onset during the recent 15 yr and their relation to body mass index (BMI) in boys.

DESIGN AND SETTING: We conducted a cross-sectional study in 1991-1993 and a combined cross-sectional and longitudinal study in 2006-2008 (The Copenhagen Puberty Study) at a tertiary center for pediatric endocrinology.

PARTICIPANTS: A total of 1528 boys aged 5.8 to 19.9 yr participated (n = 824 in 1991-1993, and n = 704 in 2006-2008). Genital and pubic hair stages as well as testicular volume by orchidometry were evaluated. Blood samples were analyzed for LH, FSH, testosterone, and SHBG.

MAIN OUTCOME MEASURES: We measured age at onset of pubertal markers.

RESULTS: Onset of puberty, defined as age at attainment of testicular volume above 3 ml, occurred significantly earlier in 2006-2008 [11.66 yr (11.49-11.82); mean (95% confidence interval)] than in 1991-1993 [11.92 yr (11.76-12.08); P = 0.025]. Significantly higher LH, but not testosterone, levels were found in the 11- to 16-yr-old boys from 2006-2008 compared to 1991-1993 (P = 0.020). BMI Z-score increased significantly from 1991-1993 [0.044 (-0.016 to 0.104)] to 2006-2008 [0.290 (0.219-0.361); P < 0.001]. Interestingly, pubertal onset and LH levels were no longer significantly different between study periods after adjustment for BMI.

CONCLUSIONS: Estimated mean age at onset of puberty has declined significantly during the recent 15 yr. This decline was associated with the coincident increase in BMI.