Age of puberty among boys dropping in US, study finds

October 22, 2012
Boys in the United States appear to be entering puberty much earlier than in the past – a trend researchers caution may have important medical, psychosocial, public health and environmental implications, according to a new study released at the American Academy of Pediatrics National Conference & Exhibition in New Orleans and published online Oct. 20 in Pediatrics.
Dr. Herman-Giddens

Dr. Herman-Giddens

“Pubertal data are an important part of monitoring the health of our nation’s children,” said Marcia Herman-Giddens, DrPH, adjunct professor of maternal and child health at The University of North Carolina Gillings School of Global Public Health and the study’s lead investigator. “Our findings suggest we need to reevaluate anticipatory guidance provided to boys – the famous ‘birds and bees’ talk may need to happen earlier – and examine what contributing factor(s) might be behind this phenomenon.”

On average, boys now begin puberty at around 9 or 10 years of age, depending on race or ethnicity – a full six months to 2 years earlier than ages documented by data several decades ago. Researchers assessed pubertal onset through visual inspection (Tanner staging) of genitalia and pubic hair growth and physical measurement of boys’ testes – tell-tale signs that sexual development has started. Unlike in prior studies, researchers included the latter measure – testicular enlargement – which is a key physical marker of puberty.
Overall, African-American boys were more likely to enter puberty earlier than white or Hispanic boys (p<0.0001). The earliest stage of puberty was found to occur at 9.14, 10.14 and 10.4 years in African-American, non-Hispanic whites and Hispanic boys, respectively. Researchers say they don’t know why these racial/ethnic differences exist.
“It may be largely genetic, as it is well known that different races have different timing in puberty, other factors being equal. But the variation also may be influenced by environmental factors,” Herman-Giddens said. “One thing that concerns me about our overall findings is the expanding gap between the onset of physical development in boys and the maturity of the brain.”She explains these two maturation processes rarely stay in sync, and early physical maturation only extends the period during which only one area of the person has developed. It’s not until late adolescence or early 20s before individuals develop mature judgment and cognitive abilities.
“Based on our study, boys are undergoing sexual development at an earlier age – earlier than in previous generations — yet they are in no way equipped to deal with the issues that come with it,” she said.The study results underscore the need for parents, medical providers, public health officials, environmental researchers, school personnel and others to recognize the apparent shift to earlier puberty and how that may impact health. In particular, she says, clinicians may consider the findings when making decisions about further evaluation or referral of boys for apparent early or late onset of development.

Researchers studied secondary sexual characteristics in 4,131 boys at well-child visits in 144 pediatric offices in 41 states between 2005 and 2010. Boys ranged in age from 6 to 16 years of age. Boys with chronic conditions or medications that could affect puberty were excluded from the cross-sectional study.

Future research should continue to include puberty studies both for validation (or refutation) and because age of onset of puberty is not static, according to Herman-Giddens. Subsequent studies also should consider potential factors causing or influencing the decreasing age of puberty in boys (e.g., nutrition, environmental disruptors, stress, maternal factors, modern lifestyle or epigenetics).The study was conducted through the AAP Pediatric Research in Office Settings (PROS) practice-based research network, a system of hundreds of pediatricians nationwide who contribute data to AAP-led scientific studies on children’s health.

A 1997 PROS study by Herman-Giddens and colleagues was the first large study to document earlier pubertal onset in U.S. girls. Until now, little information has been available about contemporary boys’ onset of puberty because boys are harder to study and there has been less interest in boys. To insure accurate data, measurement of early testicular growth is required, which is both invasive and not normally part of a well-child exam.

Co-authors of the Pediatrics report, “Secondary Sexual Characteristics in Boys: Data from the Pediatric Research in Office Settings Network,” are Michael Hussey, MS, doctoral student in biostatistics at UNC Gillings School of Public Health; Jennifer Steffes, MSW, Donna Harris, MA, and Eric Slora, PhD, from the American Academy of Pediatrics (AAP); Steven A. Dowshen, MD, from the Alfred I. DuPont Hospital for Children; Richard Wasserman, MD, MPH, from AAP and University of Vermont; Janet R. Serwint, MD, from Johns Hopkins University School of Medicine and the Academic Pediatric Association; Lynn Smitherman, MD, from Wayne State University School of Medicine and the National Medical Association; and Edward O. Reiter, MD, of Tufts University School of Medicine.



UNC Gillings School of Global Public Health contact: Linda Kastleman, communications editor, (919) 966-8317 or