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Study: Girls Entering Puberty Earlier

By Age 7, Breast Development More Common Than Reported 10 to 30 Years Ago
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WebMD Health News
Reviewed by Laura J. Martin, MD

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.

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