Washington, (March 5) Girls who are obese at the age of three may reach puberty when they are nine, according to a study that says childhood obesity could be causing earlier puberty in girls.

Joyce Lee and colleagues at the University of Michigan Health System studied 354 girls and followed them from the age of three up to 12. Almost half (168) showed signs of puberty - breast development - by their ninth birthday, the online edition of BBC News reported.

Many of these girls had a high ‘body mass index’ - a calculation of metric weight divided by height squared, which doctors use as a measure of obesity - throughout their childhood.

The researchers found that many girls, who had been overweight as children and toddlers, reached puberty aged nine.

The “normal” age for a girl to show the first signs of puberty is generally accepted as 10 and above.

Previous studies had found that girls who have earlier puberty tend to have higher body mass index, but it was unclear whether puberty led to the weight gain, or weight gain led to the earlier onset of puberty.

“Our study offers evidence that it is the latter,” Lee said in the research published in the journal Paediatrics. (IANS)