U.S. scientists found that rising rates of childhood obesity could be behind a troubling new phenomenon -- a girl will reach puberty by Grade 4, media reported on Tuesday.
Obese girls
They who followed 354 girls from age three to 12 found that those who were fatter at age three and who gained weight during the next three years reached puberty, as defined by breast development, by age nine.
The scientists said that 168 of the girls were classified as being "in puberty" by the age of nine and nearly two dozen reported having their first menstrual period by two years later.
The study from the University of Michigan's Mott Children's Hospital is published in the journal Pediatrics.
"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 Dr. Joyce Lee, the lead author.
"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," she added.
"Our study offers evidence that it is the latter," Lee said.
Early puberty in girls carries a higher risk of a wide variety of health and social problems. Other studies have shown they have higher rates of psychiatric disorders such as depression and anxiety, as well as behaviour problems such as bullying and truancy.
They're more likely to start drinking alcohol and have sex at an earlier age, and run an increased risk of teenaged pregnancy. They also have higher rates of obesity and breast cancer as adults.
Obesity rates in children have doubled over the last two decades in the west.
