Public Release: 

Research: U.S. boys also reaching puberty earlier than in past years

University of North Carolina at Chapel Hill

(Embargoed) CHAPEL HILL -- U.S. boys appear to reach puberty earlier than in past decades, a new study suggests, but why that happens is not clear and neither are the health consequences. Researchers say possible effects on health are more likely to be negative than positive, however.

"We analyzed data from the third National Health and Nutrition Examination Survey, which were collected in two phases between 1988 and 1994 on 2,114 boys aged 8 to 19 in this country," said Dr. Marcia Herman-Giddens, a researcher affiliated with the University of North Carolina at Chapel Hill. "We found that all three groups -- white, African-American and Mexican-American boys -- were significantly taller and heavier for their age than boys in previous studies, which is consistent with earlier puberty."

A report on the findings appears in the Sept. 14 issue of Archives of Pediatric and Adolescent Medicine, an American Medical Association journal. Other authors are Dr. Gary G. Koch, professor of biostatistics at the UNC School of Public Health, and biostatistics graduate student Lily Wang.

Herman-Giddens is adjunct professor of maternal and child health, also at the School of Public Health, and a senior fellow at the N.C. Child Advocacy Institute. She first made national news four years ago as author of a study indicating that U.S. girls of both white and black race appeared to enter puberty earlier than they did in years past. For unknown reasons, black girls on average start maturing about a year before whites do, that study showed.

The new research focused on information on the first signs of puberty in boys -- appearance of pubic hair and growth of the testes gathered through the federal survey, she said. The survey collects a wide variety of health and nutrition-related information to uncover positive and negative trends.

"For pubic hair, we found the average age of onset was 12.0 years for white boys, 11.2 years for African-American boys and 12.3 years for Mexican-American boys," Herman-Giddens said. "For the beginning of genital growth, the average ages were 10.1, 9.5 and 10.4 years, respectively."

Examining clinicians found that between their ninth and 10th birthdays, 4.3 percent of white boys, 21 percent of black boys and 3.3 percent of Mexican-American boys showed pubic hair development, she said. Like genital growth, pubic hair development results from the natural, genetically programmed boost in production of male hormones, but environmental factors may play a role.

The analysis suggests U.S. boys overall may be beginning puberty up to a half year earlier than previous research indicated, Herman-Giddens said. The estimate is based on the onset of pubic hair growth, assessment of which is less subjective than that of testicular growth. The difference could be greater if the genital findings are accurate.

Further studies are needed to confirm or refute the new findings on boys, the scientist said.

"Is this real, and is it healthy or not?" she said. "It's probably not healthy since earlier studies have shown that the sooner a boy starts puberty, the higher his risk is of developing testicular cancer, just as early-maturing girls are at greater risk of developing breast cancer. Then there are implications for sex education and preparing children for the psychosocial challenges of puberty, as well as the consequences of earlier sexual activity."

Changes in when children as a group begin the physical maturation of puberty are important to understand since they could reflect, in part, harmful environmental conditions such as exposure to chemical contaminants, the scientist said. Dietary and other lifestyle changes in society also could play a role. Unfortunately, staffers with the national survey project have stopped collecting data on pubertal development.

Physicians and others may dispute the genital findings since such measurements are imprecise, Herman-Giddens said, but she believes few will dispute the findings on pubic hair growth. Differences between the races remained even after researchers controlled for height and weight.

NHANES data are considered good because subjects are selected to be representative of the entire U.S. populations and because information is gathered in a standard way across the country.

"Personally, I believe changes in when puberty starts in boys and girls is an important public health issue in this country," Herman-Giddens. "It's good that these findings get attention because they stimulate research into the health implications, which we really do need to know about."


Genentech Inc. supported the new study.

Note: Herman-Giddens can be reached at (919) 542-2529 or 542-5573. E-mail:
UNC News Services Contact: David Williamson, (919) 962-8596
UNC School of Public Health Contact: Lisa Katz, (919) 966-7467

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