Are boys also beginning puberty earlier than before?

Girls have been the focus of stories looking at the early onset of puberty, but a new study from Sweden indicates that some boys also may have been undergoing early puberty.

Researchers used school records to find the heights and weights for boys who were born in Gothenberg, Sweden, from January 1, 1947, and onward and then every 5 years from 1951 to 1996: each birth cohort from 1947-1991 had 375 boys, the 1996 birth cohort had 340 boys, and the total cohort included 4090 boys. For each participant, they estimated childhood body mass index (BMI), maximum growth velocity during puberty, and peak height velocity (PHV) using the data.

Most of the participants were white and the average age at PHV was 13.9 years. Linear regression showed that a significant link between the year of birth and age at PHV existed. For every decade increase in birth, the age at PHV was found to be 1.5 months earlier. After considering BMI, the age at PHV was 1.2 months earlier for each decade increase in birth year. When the researchers looked at a subset of the data, which included only boys born in Sweden to parents who also had been born in Sweden, they found similar results, indicating that their results weren’t predicated on the demographic changes in Sweden’s population.

When discussing the strengths of their study, the researchers pointed to the long period of time studied, which allowed them to distinguish between trends and temporary changes. Using PHV provided them with an objective measurement for pubertal timing. They also said that the small range of prepubertal BMI in the cohort may have cause an underestimation of the importance of it on prepubertal timing.