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. 2019 Sep 1;173(9):860-865.
doi: 10.1001/jamapediatrics.2019.2315.

Secular Trends in Pubertal Growth Acceleration in Swedish Boys Born From 1947 to 1996

Claes Ohlsson  1 , Maria Bygdell  1 , Jimmy Celind  1 , Arvid Sondén  2 , Anders Tidblad  3 , Lars Sävendahl  3 , Jenny M Kindblom  1
Affiliations

Secular Trends in Pubertal Growth Acceleration in Swedish Boys Born From 1947 to 1996

Claes Ohlsson et al. JAMA Pediatr. .

Abstract

Importance: A secular trend for earlier menarcheal age has been established in girls but there are few studies of pubertal timing for boys.

Objective: To determine if there is a secular trend for earlier pubertal timing among boys.

Design, setting, and participants: For this population-based retrospective cohort study conducted in Gothenburg, Sweden, we collected heights and weights from school health records for boys born consecutively from January 1 and onwards in 1947 and every 5 years from 1951 to 1996 (n = 375 for each birth cohort from 1947-1991, n = 340 for the birth cohort in 1996, and n = 4090 for the total cohort). We estimated age at the peak height velocity (PHV), the maximum growth velocity during puberty, and childhood body mass index (BMI) at age 8 years for all study participants. The data were analyzed during 2018 and 2019. Boys were eligible if they had a complete personal identity number and data to calculate their age at PHV and childhood BMI. Approximately 2.4% of the original study population was excluded because they lacked a personal identity number, and in the remaining study population, 4090 (69%) had sufficient data to calculate childhood BMI and age at PHV.

Exposures: The exposure was birth year and a potential confounding factor was childhood BMI.

Main outcomes and measures: The outcome was age at PHV.

Results: Of the 4090 participants, most were white and the mean (SD) age at PHV was 13.9 (1.1) years. A linear regression model revealed a significant association between year of birth and age at PHV. Age at PHV was 1.5 months earlier for every decade increase in birth year (95% CI, -1.72 to -1.19; P < .001). After adjusting for childhood BMI, age at PHV was 1.2 months earlier per decade increase in birth year (95% CI, -1.41 to -0.89). All analyses were repeated in the subgroup of boys born in Sweden and with parents born in Sweden with similar results, indicating that the secular trend was not explained by demographic changes in the population between 1947 and 1996.

Conclusions and relevance: We provide evidence of a secular trend for earlier pubertal timing in boys that is partially explained by an increased childhood BMI, but other factors that are unknown contribute.

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Conflict of interest statement

Conflict of Interest Disclosures: Dr Ohlsson reported grants from Wallenberg Foundation, the Swedish Research Council, and Novo Nordisk Foundation during the conduct of the study. Dr Kindblom reported grants from Anna Ahrenberg foundation, the Swedish Research Council, and the Swedish state under the ALF agreement during the conduct of the study. No other disclosures were reported.

Figures

Figure 1.
Figure 1.. Mean Age at Peak Height Velocity (PHV) for Boys Included in the BMI Epidemiology Study Cohort Born From 1947 to 1996
Values are presented as mean (95% CI), and statistically significant differences vs the birth cohort in 1947 were observed from the birth cohort in 1976 and after (P < .01). The P for trend is <.001.
Figure 2.
Figure 2.. Distribution of Age at Peak Height Velocity (PHV) for Boys Included in the BMI Epidemiology Study Cohort Born From 1947 to 1996
Figure 3.
Figure 3.. Mean Age at Peak Height Velocity (PHV) Adjusted for Childhood Body Mass Index (BMI) for Boys Included in the BMI Epidemiology Study Cohort Born From 1947 to 1996
Values are presented as mean (95% CI). The P for trend is <.001.
Figure 4.
Figure 4.. Mean Age at Peak Height Velocity (PHV) Among a Subgroup of Boys Born From 1947 to 1996 in Sweden and With Parents Born in Sweden
Values are presented as mean (95% CI). The P for trend is <.001.
See this image and copyright information in PMC

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