Study: overweight more common among early-maturing girls, especially minorities

CHAPEL HILL -- American girls who mature earlier than others also are more likely to be overweight, a new University of North Carolina at Chapel Hill study shows. Early-maturing black girls faced the highest risk of obesity with 57.5 percent of them being at or above the 85th percentile of U.S. adolescent female body mass index, a measure of relative weight.

Because many health experts believe girls as a group may develop physically sooner than they did in past generations and because of rapidly increasing rates of type 2 diabetes, obesity-prevention efforts should target all U.S. girls, especially blacks, researchers said.

A report on the findings appears in the April issue of the American Journal of Public Health.

"Recent surveys show an alarming trend of increased prevalence rates of overweight in U.S. adolescents, particularly among minorities," wrote authors Drs. Linda S. Adair and Penny Gordon-Larsen, associate professor and assistant professor, respectively, of nutrition at the UNC schools of public health and medicine.

"In the 1960s, 21.1 percent of black females were overweight," the two wrote. "By the mid-1990s, the percentage had increased to 30.7 percent. Data from the Third National Health and Nutrition Examination Survey for 1988 through 1991 also showed that 23.4 percent of Mexican-American female adolescents aged 12 to 17 years were overweight."

Adair and Gordon-Larsen set out to learn whether a clear relationship existed between early maturation and obesity, a link proposed by Harvard biologist Rose Frisch in the early 1970s.

They analyzed information from 6,500 Asian-American, Hispanic, black and white girls who participated in the National Longitudinal Study of Adolescent Health and divided the girls into three groups depending on the age at which they first menstruated. On average, they found that early maturing girls were shorter by more than a half inch and heavier by more than eight pounds than those who matured later.

"Also, significantly higher proportions of African-American and Hispanic girls had their first period before age 11, and a significantly higher proportion of Asian-American girls had their first period after their 14th birthday," Adair said. "Adolescent girls who had their first period before their 11th birthday were two times more likely to be overweight than girls who begin menstruating later."

Early-maturing black girls were 2.57 times more likely to be overweight than white girls who matured neither early nor late, she said.

"Our study could not address the issue of whether having more body fat causes girls to mature earlier, but it does document a strong relationship," Adair said.

"We're interested in this question because, besides diabetes, many health problems have been linked to being overweight, including atherosclerosis, heart attacks and strokes later in life," she said. "Also, we know that earlier-maturing girls tend to become sexually active earlier than other girls."

The UNC-based National Longitudinal Study of Adolescent Health, also known as Add Health, is the largest study of U.S. adolescents ever conducted. Data from the larger study, led by Drs. J. Richard Udry, professor of maternal and child health, and Peter Bearman, now at Columbia University, came from detailed, confidential surveys of 17,666 teen-agers about their experiences, practices and attitudes.

The National Institute of Child Health and Human Development, the Carolina Population Center and numerous other agencies funded Add Health. A recent, widely reported study from Add Health data showed that teen pledges to remain virgins until marriage often succeeded in helping younger teens postpone sex. In 1997, UNC's Dr. Marcia Herman-Giddens published a widely cited paper in Pediatrics indicating that for unknown reasons, U.S. girls might reach puberty earlier than they did in the past.

Note: Adair can be reached at (919) 966-4449, linda_adair@unc.edu; Gordon-Larsen at 933-9966, pglarsen@unc.edu. Both will be attending meetings when this paper appears but will return messages as soon as possible.

School of Public Health