Those protective parents that cram their beloved girls should know that this is exactly what will break the girls away from home.

A new research showed that childhood obesity and overweight in the US could be linked to an earlier onset of puberty in girls. The team from the University of Michigan C.S. Mott Children's Hospital pointed out that a higher body mass index (BMI) score in girls as young as age 3, and large increases in BMI between 3 years of age and first grade are linked to earlier puberty, defined as the presence of breast development by age 9.

Previous researches did not investigate girls younger than 5. "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, pediatric endocrinologist Joyce Lee, a member of the Child Health Evaluation and Research (CHEAR) Unit in the U-M Division of General Pediatrics, and assistant professor in the Department of Pediatrics and Communicable Diseases at the U-M Medical School. "Studies have suggested that girls in the US are entering puberty at younger ages today than they were 30 years ago," said Lee.

As childhood obesity rates also have significantly risen during the same time period, researchers have supposed that childhood obesity could be linked to a trend of earlier puberty in girls. "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," said Lee.

The research team investigated a pool of 354 girls from various socioeconomic backgrounds in 10 regions of the US employing data from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development study.

The researchers focused on BMI and weight status recordings from ages 3 to 12, but also puberty symptoms like breast development and the ages of the onset of menstrual periods.

Girls were considered at risk for overweight if their BMI was between the 85th and 95th percentiles, and defined as overweight if their BMI was greater than the 95th percentile for average weight for their age and height. By fourth grade, 30 % of the girls were at risk for overweight or even already overweight and 47 % were considered "in puberty".

About 7 % of the girls were reported having their first menstrual period by the sixth grade. Higher BMI at all ages, even between 3 and first grade (well before the onset of puberty), were discovered to be heavily linked to an earlier onset of puberty in girls.

Earlier onset of puberty is connected to higher rates of psychological and behavioral problems, like earlier initiation of alcohol use and sexual intercourse, but also higher rates of adult obesity and reproductive cancer. "Beyond identifying how obesity causes early puberty, it's also important to determine whether weight control interventions at an early age have the potential to slow the progression of puberty," notes Lee.