Increasing rates of childhood obesity may be contributing to an earlier onset of puberty in girls, researchers say.

A team at the University of Michigan C.S. Mott Children's Hospital said that a higher body mass index score in girls as young as 3 are linked to breast development by age 9.

"Our finding that increased body fatness is associated with the earlier onset of puberty provides additional evidence that growing rates of obesity among children in this country may be contributing to the trend of early maturation in girls," said lead author and pediatric endocrinologist Dr. Joyce Lee.

Studies have suggested that girls in the United States are entering puberty at younger ages today than they were 30 years ago, just as obesity rates have risen.

Lee said her research starts to answer the question of whether increased weight causes early puberty, or the other way around. She said it looks more likely that obesity is the cause.

Lee's team studied at 354 girls from diverse socioeconomic backgrounds in 10 regions.

Studies have shown that earlier onset of puberty can lead to higher rates of behavioral problems, including earlier initiation of alcohol use, sexual intercourse and increased rates of adult obesity and reproductive cancer.

The study was published in the March issue of the journal Pediatrics.