Boys are entering puberty earlier, large study shows

BMJ 2012; 345 doi: (Published 31 October 2012) Cite this as: BMJ 2012;345:e7331
  1. Janice Hopkins Tanne
  1. 1New York

A study of 4131 boys in the United States and Canada showed that puberty is beginning six months to two years earlier than in previous studies. Researchers from the University of North Carolina at Chapel Hill and other leading medical schools and research institutions published the report online in Pediatrics.1

Recent studies of US girls have indicated that they are entering puberty about a year earlier than 40 years ago, but data on US boys entering puberty are 20 years old.

In the new study boys showed secondary sexual characteristics earlier than in previous US studies and in the 1969 British study that was commonly used for pubertal norms,2 the researchers said.

They wrote, “Our data suggest that US boys are beginning genital and pubic hair growth earlier than several decades ago, in concordance with recent reports on girls. These data are consistent with recent reports from other countries, such as Denmark, Sweden, Great Britain, Italy, and China.”

Assessment of boys’ pubertal status used Tanner staging, a five stage visual method that looks at development of sexual characteristics such as genital and pubic hair growth. Stage 1 is prepubertal, while stage 5 is fully mature. The study also used orchidometry to measure testicular volume by comparing testicle size with standardized plastic beads.

African American boys entered stage 2 genital development at 9.14 years, while Hispanic boys entered it at 10.04 years and white boys at 10.14 years. African American boys were more likely than white and Hispanic boys to have genital and pubic hair development at any given age.

In the current study white US boys entered puberty 1.5 years earlier than the boys in the landmark study of institutionalized London boys by British researchers 40 years ago: 10.14 versus 11.6 years.

However, comparisons with earlier data were limited, the researchers said, because of lack of early data on ethnic minorities and because of differences in study methods, socioeconomic status, age at enrollment, and small numbers of participants. Very few European or US studies have included testicular volume.

The authors said that they didn’t know what might cause early puberty. However, they commented that environmental factors such as exposure to chemicals, changes in diet, less physical activity, and perhaps overweight and obesity may be related to early puberty “and may not reflect healthy conditions.”

Their study was not designed to report hormonal changes.

Boys were seen in “well child” examinations by 212 practitioners from 41 US states and one Canadian province between 2005 and 2010. The office based reporting clinicians were mostly pediatricians, but they also included one family medicine doctor and 15 nurse practitioners.

Assessing male puberty is difficult because there is no clear marker like menarche. “Male pubertal stages are harder to assess visually than girls’ stages, and orchidometry, an intrusive procedure, is not part of well-child exams,” the report says.


Cite this as: BMJ 2012;345:e7331