Girls are reaching puberty earlier and obesity is a major factor, study finds

(UPI) -- A recent study has found that girls in the U.S. are entering puberty at younger ages and that obesity may be a major factor.

The study, which looked at more than 1,200 girls ages 6 to 8 in the San Francisco area, the Cincinnati area and New York City, and followed up with them from 2004 to 2011, was published in the journal Pediatrics.

Obesity was strongly linked to early puberty and girls with a higher body mass index (BMI) were more likely to hit puberty at a young age.

"The influence of BMI on the age of puberty is now greater than the impact of race and ethnicity," said study researcher Dr. Frank Biro. “These girls were born and raised in the midst of an obesity epidemic. This is yet another impact of obesity epidemic in this country."

Researchers found that white girls entered puberty on average at 9.7 years old, three to four months younger than the average age that scientists recorded in 1997 and significantly younger than the age recorded in the 1960s.

Black girls started puberty at 8.8 years old on average, on par with the 1997 study. Hispanic girls reached puberty at the average age of 9.3 years and the average age for Asian girls was 9.7 years.

The results of the study are similar to what researchers in other countries have found. A 2009 Danish study found that girls experienced breast development nearly a year earlier than those born 15 to 16 years prior.

The early growth of breasts does not necessarily change the age of first menstruation, the authors noted.

"With each new study in the past two decades, we hope the age of 'early puberty' has bottomed out," wrote researcher Marcia Herman-Giddens in an editorial that accompanied the study. "When each 'new study' has been published, however, we find the trend toward early puberty has continued."

"Each individual girl is exposed to multiple factors in today’s environment, many not present decades ago, that may potentially influence her pubertal onset," she wrote.

Herman-Giddens points out that meat and dairy-heavy diets, insulin resistance, hormone-laced body and hair care products and high-stress families are all factors that may contribute to earlier puberty.

Biro said that early onset of physical maturation has social consequences, too. "There's a greater mismatch now between how [girls] look, and how they behave and how they interact with other people."