U.S. Girls Are Hitting Puberty Earlier, And Our Obesity Epidemic May Be To Blame

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Girls are entering puberty much earlier than they used to, according to a new study published in the journal Pediatrics, and some begin maturing when they’re just eight years old. Researchers believe the trend is linked to the national obesity epidemic, since girls with a higher Body Mass Index (BMI) are more likely to develop breast tissue at an early age.

Those conclusions are the culmination of a long-term study that tracked more than 1,200 girls between the ages of six and eight. Researchers monitored the participants’ BMI and physical maturation from 2004 to 2011, and found that many of the girls began developing breast tissue in second grade. The average age for breast development was eight years and ten months for African-American girls; nine years and four months for Hispanic girls; and nine years and eight months for white and Asian girls. Heavier girls tended to be on the earlier end of that range, around eight years old, while girls with lower BMIs didn’t show signs of puberty until around age ten.

The study’s lead researcher, Dr. Frank Biro, concluded that obesity appears to be a “prime driver” behind early breast development. “BMI is, we found, the biggest single factor for the onset of puberty,” Biro told NBC News. Biro suggests that extra weight might trigger puberty because it leads the body to believe it already has enough energy and resources to sustain that process.

Breast development signals the beginning of female puberty. Girls typically get their periods about two to four years after their breast tissue begins to develop. Biro didn’t track the girls’ periods for this study, so he and his colleagues aren’t sure if obesity is also linked to earlier menstruation.

An estimated 12.5 million kids in the U.S. are considered to be obese, according to the Centers for Disease Control. The obesity epidemic continues to take a outsized toll on Americans’ health, although there are some slow signs of progress in this area. Public schools have been attempting to tackle the issue by mandating healthier school lunches and banning junk food from vending machines in cafeterias. Nonprofit groups are also working to get more fresh produce in urban stores. Those approaches may be working: The obesity rate among low-income children is currently dropping.

Campaigns to raise awareness about obesity walk a fine line, however. Some attempts to take on childhood obesity end up placing too much emphasis on weight, ultimately shaming kids about what their bodies look like. That dynamic has fueled the rise of disordered eating among U.S. youth.

Biro is wary of that dynamic, and cautions parents against taking a negative approach to heavier girls who may be developing at an early age.

“Parents of these early maturing kids have to be more watchful,” he told NBC News. “But I don’t want to have a nation of patients with eating disorders. We need to figure out what are healthy weights for our kids. We want them to be comfortable with their bodies.”