By DAVID WILLIAMSON UNC-CH News Services
CHAPEL HILL -- Girls in the United States appear to be entering puberty earlier than they did in the past, according to a new American Academy of Pediatrics study, but researchers are not sure why.
Black girls begin puberty shortly before age 9 on average, while white girls begin just before age 10, the study shows. Before age 8, 27 percent of blacks and almost 7 percent of whites already have begun developing breasts, growing pubic and underarm hair or both. Why racial differences occur also is unknown.
"No adequate studies have been done in the United States on puberty norms," said Dr. Marcia E. Herman-Giddens of the University of North Carolina at Chapel Hill School of Public Health. "When I was in clinical practice examining children, colleagues and I noticed that an unusually large number of them already were developing sexual characteristics. We found no North American standards for normal development, and we did this work to determine average ages when puberty begins in young girls in this country."
A report on the study, which analyzed information from 17,077 girls seen in doctors' offices nationwide, appears in the April issue of Pediatrics, a medical journal. Herman-Giddens, adjunct professor of maternal and child health and medical director of the N.C. Child Fatality Prevention Team, was principal investigator.
Researchers studied girls seen for physical examinations at 225 pediatrics practices involved in the Pediatric Research in Office Settings Network, a collaborative program of the American Academy of Pediatrics that studies large groups of patients. About 90 percent of subjects were white; the rest were black.
Analysis revealed that by their ninth birthday, 48 percent of black girls and slightly less than 15 percent of white girls had begun breast or secondary hair development or both. Average ages for beginning menstruation were about 12 years and two months for blacks and 12 years and 10 months for whites.
Three percent of black girls and 1 percent of whites already show some sexual development at age 3.
"All of us in pediatric practice had a sense that girls were developing earlier, but we were still somewhat surprised at how young many of them were," Herman-Giddens said. "Quite a significant number of girls in the second and third grades are beginning puberty and may not learn anything about it through health classes until much later."
Educating children early about how their bodies change would spare many of them psychological and social difficulties associated with sexual maturity, she said. Possible explanations for the earlier onset of puberty include better nutrition, especially among blacks, and more estrogen-related products in the environment such as certain plastics, insecticides and certain hair products.
"Children who show early signs of sexual development sometimes can get very detailed and expensive medical evaluations to make sure they don't have some serious illness, and it may be that some of these children are being treated unnecessarily," Herman-Giddens said. "This work could cause standards for such evaluations and treatment to be re-evaluated."
Knowing that girls enter puberty earlier also will allow parents to better prepare them, she said.
Besides Herman-Giddens, authors of the Pediatrics report are Dr. Eric J. Slora, Cynthia M. Hasemeier and Dr. Richard C. Wasserman of the American Academy of Pediatrics; Dr. Carlos J. Bourdony of the University of Puerto Rico; and Manju V. Bhapkar and Dr. Gary G. Koch of biostatistics at UNC-CH.
Genentech Inc. and the U.S. Maternal and Child Health Bureau supported the study.
Note: Herman-Giddens can be reached at (919) 966-2253 (w) or 542-5573 (h). She also may be reached via her cell phone, (919) 215-5418.
Contact: David Williamson