MONDAY, Aug. 9, 2010 (HealthDay News) -- The onset of puberty is continuing to drop among American girls, with many girls as young as 7 and 8 now showing the beginnings of breast development, new research shows.
Rising rates of childhood obesity -- long linked to earlier sexual development -- may be to blame, experts say.
In the study, more than 1,200 girls ages 6 to 8 from Cincinnati, East Harlem, N.Y. and San Francisco were examined on two occasions between 2004 and 2006 by two different female pediatricians or nurse practitioners who felt for the presence of breast tissue.
"We wanted to be careful not to mistake fatty deposits for actual breast tissue," explained study author Dr. Frank Biro, director of adolescent medicine at Cincinnati's Children's Hospital.
Among 7-year-olds, about 10.4 percent of white girls, 23.4 percent of black girls and almost 15 percent of Hispanic girls had started developing breasts, the team report in the September issue of Pediatrics. Among 8-year-olds, 18.3 percent of white girls, about 43 percent of black girls and just under 31 percent of Hispanic girls showed evidence of breast development.
The figures suggest a rise in early-onset puberty compared to similar studies conducted earlier.
For 7-year-old white girls, especially, they show a doubling of the rate from as recently as a decade ago, Biro said. One study found that about 5 percent of white 7-year-old girls and 10.5 percent of 8-year-olds were showing breast development.
For black girls, the rate of breast development in that study was 15.4 percent for 7-year-olds and 36.6 percent for 8-year-olds.
The earlier data did not include information on Hispanic girls.
Experts called the findings alarming. In terms of women's health, early puberty, including younger ages at menarche, or first menstrual cycle, is associated with a higher risk of breast cancer throughout the life span, Biro said.
In addition, developing early is associated with psychological and social pressures that young girls may be ill-equipped to handle, including sexual advances from older boys and men, said Dr. Marcia Herman-Giddens, adjunct professor of public health at the University of North Carolina, Chapel Hill.
Girls may look older than their age, but mentally, they are much the same as other 7-and 8-year old girls, said Herman-Giddens, who led the earlier study.
"They really miss out on a good part of their childhood," she said. "When my study came out, I received very sad, poignant letters and e-mails from young women who had been early developers, how horrible it was to have older boys and young men hitting on them and sexual feelings they didn't understand."
What's driving the earlier maturation? Increasing weight at a young age seems to be a main culprit, Biro said. Girls who developed breasts early tended to have a higher body-mass index (BMI) than those who didn't. Though much is still unknown about how high BMIs kick start puberty, fat cells produce leptin, a hormone involved in the onset of pubertal maturation, Biro noted.
Biro and his colleagues are also conducting analyses of the girl's blood and urine to determine if environmental exposures to chemicals could be contributing, but those results have yet to be completed.
And even if environmental exposures are found to play a role, the association between excess weight gain and early onset of puberty is very strong, Biro said.
"Girls who go into puberty earlier have a higher BMI than those who go into it later, and studies have shown that they typically persist in having a higher BMI throughout life," Biro said.
If a child is showing early signs of puberty, experts recommend an evaluation by a pediatrician or an endocrinologist to rule out medical problems.
Parents and pediatricians can also help girls maintain a healthy weight through proper nutrition and exercise, Herman-Giddens said.
Even with those steps, some girls will simply be predisposed to developing earlier than others and that's perfectly normal, the experts said. And while early development poses risks for girls, parents can help their girls by talking with them, Herman-Giddens said.
"Whatever they do, parents cannot just ignore it," she said. "Women have told me that their parents completely shut down and did not know how to cope or help them at all. That is very hard on the child. They have to reassure the child they are normal, they are just early."
A second study published in The Lancet, led by Mildred Maisonet of Emory University, Atlanta, examined at the histories of 4,000 British girls aged 8 to 14. Her team found that girls whose mothers had experienced menarche before age 12, who smoked during pregnancy or who were firstborn children were more likely to experience early onset of puberty compared to other girls.
Daughters of obese mothers were also more likely to be overweight themselves, and were more likely to show breast development at an early age, the study found. Birth weight or birth length did not influence the timing of puberty, yet a rapid increase in BMI during infancy was associated with earlier onset of puberty.
There's advice on talking to children about puberty at the Nemours Foundation.