Increasing rates of childhood obesity and overweight in the United States may be contributing to an earlier onset of puberty in girls, say researchers at the University of Michigan C.S. Mott Children’s Hospital.

In a new study published in the March issue of the journal Pediatrics, the researchers reveal 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 associated with earlier puberty, defined as the presence of breast development by age 9. This longitudinal study is unique in that it included girls younger than age 5 to examine the association between weight status and timing of puberty.

“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,” says lead author and U-M pediatric endocrinologist Joyce Lee, M.D, MPH.

Studies have suggested that girls in the United States are entering puberty at younger ages today than they were 30 years ago, says Lee. Since rates of childhood obesity also have significantly increased during the same time period, researchers have speculated that childhood obesity may be contributing 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,” says 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.

To study the association between weight in early childhood and the onset of puberty, Lee and her colleagues looked at 354 girls from diverse socioeconomic backgrounds in 10 regions of the United States using data from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development study.

Along with recording BMI and weight status from ages 3 to 12, the study looked at multiple outcomes of puberty in girls, including breast development as well as children’s ages at the onset of menstrual periods.

For this study, girls were classified as 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 weight based on age and height.

The study found that by fourth grade, 30 percent of the girls were either at risk for overweight or already overweight. Additionally, 168 of the study participants were considered “in puberty” by fourth grade. Nearly two dozen of the girls in the study reported having their first menstrual period by sixth grade.

Higher BMI scores at all ages were found to have a strong association with an earlier onset of puberty in girls. Earlier onset of puberty also was associated with higher BMI change between age 3 and first grade – a period well before the onset of puberty.

Studies have shown that earlier onset of puberty can lead to higher rates of behavioral problems and psychosocial stress, as well as earlier initiation of alcohol use, sexual intercourse, and increased rates of adult obesity and reproductive cancer. That’s why Lee says it is important for future studies to identify exactly how increased body fat leads to earlier puberty in girls to prevent these adverse effects.

“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.

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In addition to Lee, co-authors are: from Boston University School of Public Health Danielle Appugliese, MPH; from the University of Michigan Niko Kaciroti, Ph.D., and Julie C. Lumeng, M.D.; and from the University of Arkansas at Little Rock Robert F. Corwyn, Ph.D., and Robert H. Bradley, Ph.D.

The study was funded by grants from the National Institute of Child Health and Human Development and the American Heart Association.

Reference: Pediatrics, Vol. 119, No. 3.

University of Michigan Health System