Epidemic obesity rates are the "prime driver" in a nationwide trend toward earlier and earlier breast development in young girls according to new research.
In a paper published Monday in the journal Pediatrics, researchers found that the average age of thelarche, or onset of breast development, was earlier than previously recorded for white girls, and that a high body mass index, or BMI, was a strong indicator of early puberty.
While the study's authors said it remained unclear whether early breast development led to early onset of menstruation, they said the trend toward earlier sexual development raised numerous clinical issues.
"Girls with earlier maturation are at risk for lower self-esteem and higher rates of depression," wrote Dr. Frank Biro, a pediatrician at Cincinnati Children's Hospital.
"They are more likely to be influenced by older peers and more deviant peers, and initiate intercourse, substance abuse and other norm-breaking behaviors at younger ages," Biro and his colleagues wrote.
The authors noted also that early maturation was associated with increased risk of breast, ovarian and endometrial cancer.
Researchers tracked the development of more than 1,200 girls in San Francisco, New York and Cincinnatti. The girls were enrolled in the study when they were between the ages of 6 and 8, and were examined periodically from 2004 to 2011.
Among other findings, the study's authors said that breast development in white non-Hispanic girls began at a median age of 9.7 years, earlier than previously reported. Black girls were found to experience breast development earlier, at a median age of 8.8 years, and Hispanic and Asian girls were found to experience development at a median age of 9.3 and 9.7 years, respectively.
The authors said that girls who were in the 50th percentile or higher for body fat content were progressively more likely to have reached early breast development than those below the 50th percentile.
The research has several possible limitations, according to authors, including the possibility that the study sample does not represent the nation as a whole.