Aug. 9, 2010 -- The age of puberty is declining for girls, with more girls developing breasts by age 7 than in years past, according to a new study.
Ethnicity plays a role in earlier puberty, says researcher Frank M. Biro, MD, director of the division of adolescent medicine at Cincinnati Children's Hospital Medical Center, Cincinnati. So does body composition.
"We found that girls who are African-American matured before whites, and that's been shown in several studies," Biro tells WebMD. "White girls are maturing earlier than they had before, compared to 20 years earlier."
In his study of 1,239 girls, 10% of whites, 23% of African-Americans, and 15% of Hispanic girls had breast development indicating onset of puberty by age 7, Biro found.
Biro can't give an average age of puberty at this time, he says, because many girls in the study have not yet developed breasts. Over time, further analysis is expected to provide that and other information.
The study is published online in the journal Pediatrics.
Age of Puberty Study: Details
Biro and his colleagues took a ''snapshot in time'' or cross-sectional look at girls who were recruited at three sites when they were aged 6 to 8 in 2004-2006. They lived in East Harlem, New York, Cincinnati, or the San Francisco Bay area.
The researchers assessed the onset of puberty by a standard measurement of breast development.
They compared the findings to a 1997 study of age of puberty. They found that:
- 10.4% of white girls in the current study had breast development, compared to 5% in the 1997 study.
- 23.4% of African-American girls had beat development, compared to 15.4% in the 1997 study.
Besides ethnicity, body mass index or BMI was found to play a role in onset of puberty, Biro's team found. Girls who had breast development at age 7 were more likely to have a higher BMI. Body fatness has been linked with onset of puberty in girls, other research by Biro and others has shown.
The study was conducted within the Breast Cancer and the Environment Research Centers (BCERC), established in late 2003 as a partnership with the National Institute of Environmental Health Science and National Cancer Institute, which funded the research. Research suggests that women with breast cancer started their periods earlier, and that those with earlier onset of periods have an increased breast cancer risk.
Earlier Puberty: Explaining the Findings
The researchers also collected urine and blood specimens from the girls to look at levels of compounds called endocrine-disrupting chemicals, Biro says, to see what role these environmental exposures might play in early puberty.
''It appears that some of the endocrine-disrupting chemicals are interacting with body composition and this may be the reason some girls are going into puberty earlier and others later," Biro tells WebMD. "That would have to be speculation," he says of the interaction idea. "But we do know BMI is doing it."
Among 6- to 11-year-olds, obesity has increased from 6.5% in 1976-1980 to 19.6% in 2007-2008, according to the CDC.
Endocrine-disrupting compounds or EDCs are found in a host of consumer products, ranging from personal care products such as antibacterial soaps to furniture and anti-stain fabrics.
Earlier Puberty Study: Other Thoughts
Although further research is likely to pinpoint the cause of earlier puberty in girls, the focus now should be on more practical matters, says Warren Seigel, MD, a member of the American Academy of Pediatrics' Committee on Adolescence and chair of the department of pediatrics at Coney Island Hospital in Brooklyn.
"Instead of debating the cause only, let's talk about what we can do right now, and [that is], we have to be on guard," Seigel tells WebMD.
Earlier Puberty: Tips for Parents
Until more is known about what drives earlier puberty in girls, Biro suggests families try ''living greener, trying to minimize exposure to chemicals in the environment, and part of that might be using safer personal care products."