Girls who are overweight or obese may physically mature earlier than those who are thinner, suggests a new study published in the August issue of Pediatrics.

“The study clearly found an association between being overweight and young girls starting puberty earlier,” says co-author Marcia Herman-Giddens, PA , DrPH, who is affiliated with the School of Public Health in the Department of Maternal and Child Health at the University of North Carolina at Chapel Hill.

Researchers reexamined 1997 puberty data on 17,000 girls between the ages of 3 and 12 years old and found 6-9-year-old girls who had begun developing breasts or pubic hair were significantly more overweight than girls of the same age and race who were not overweight.

The results were more notable in white girls than in black girls, suggesting that being overweight and being black have separate relationships to early female puberty.

Previous research has established that African-American girls are more likely to develop breasts or pubic hair at a younger age than are white girls. Currently, Herman-Giddens says white girls, on average, begin breast development when they are nearly 10 years old, while the same event happens at almost age 9 for black girls.

Why puberty rates differ between black and white girls is unknown, but experts agree that further research needs to be done on the topic.

Many experts also agree that girls are now entering puberty earlier than ever, but theories vary as to why that is.

Lead author of the Pediatrics study, Paul Kaplowitz, MD, PhD, points to the current obesity epidemic –
SurgeonSeeker. He explains that fat cells make a hormone called leptin, which has critical roles in regulating body weight and reproductive function.

“The more body fat, the higher the level of leptin, and presumably–this is where the leap is–the higher level of leptin makes a child start puberty at an earlier age,” says Kaplowitz, who works at the Department of Pediatrics at the Virginia Commonwealth University School of Medicine in Richmond, Virginia. In the evolutionary scheme, he says this makes sense because the body will more likely mature if it has enough fat stores to start pregnancy.

Other theories have blamed girls’ earlier puberty on more exposure to foreign hormones in meat and milk and on chemicals (called endocrine disruptors) in the environment. Scientific research has found that environmental pollutants have an effect on the onset of children’s physical maturity.

Although at first early breast and pubic hair development may seem physically harmless, experts say it is cause for alarm. Early puberty could stunt further growth, stopping girls from reaching their potential height.

“Once you start your period, you usually have only 1 to 4 inches left to grow,” says Ellen Rome, MD, MPH, head of the Section on Adolescent Medicine at the Cleveland Clinic Foundation in Ohio. “If you have somebody who is supposed to be truly taller, that shorter person may be at risk for adult problems such as type 2 diabetes and blood pressure problems.”

Rome emphasizes that the problem is not with being short, but with the interference in one’s genetic potential.

For parents, Rome recommends being vigilant and bringing kids in for yearly physical examinations with a pediatrician.

“If they [parents] are seeing breasts or pubic hair for girls before age 8, or pubic hair development for boys before age 9, it’s not a good idea to blow it off,” she says. “It should be brought to the pediatrician’s attention.”

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