Girls are developing breasts at younger and younger ages, a new study confirms. And upward trends in childhood obesity seem to be playing a major role.
Researchers found African American girls started getting breasts just before they turned nine, on average. Among white girls the average age was about nine and a half - a few months earlier than in the 1990s.
The findings "confirm an ongoing downward trend in pubertal timing among U.S. girls," said Dr. Anders Juul.
"It's been worrying for the U.S. as well as the rest of the world," Juul said. He heads the Department of Growth and Reproduction at Rigshospitalet in Copenhagen, Denmark, and wasn't involved in the new report.
The data come from a long-term study of more than 1,200 girls in and around San Francisco, Cincinnati and New York City. Girls were enrolled in the study between ages six and eight and followed with annual or semi-annual visits.
At each visit, staff assessed breast development using Tanner stages, which measure how far along a young person is in puberty.
African American girls first showed signs of breast development at eight years, 10 months, on average. That compared to nine years, four months among Hispanic girls and nine years, eight months among white and Asian girls.
For white girls, puberty hit about four months earlier than in a 1997 study that also measured breast development. That study concluded girls were entering puberty earlier than in the past.