Girls Going Through Puberty Earlier and Earlier

SF Gate
November 4, 2013

High schooler Rachael Cornejo, looking for clothes in her bedroom to lend sister Hannah in Berkeley, says talking about puberty and related issues needs to happen earlier in kids' lives. Photo: Raphael Kluzniok, The Chronicle.
High schooler Rachael Cornejo, looking for clothes in her bedroom to lend sister Hannah in Berkeley, says talking about puberty and related issues needs to happen earlier in kids’ lives. Photo: Raphael Kluzniok, The Chronicle.

Girls are starting puberty at younger ages – a full year earlier than previously reported in some cases – and the main factor associated with early breast development is obesity, according to a new long-term study released Monday.

Researchers in the Bay Area, New York and Cincinnati have been following the sexual maturation of more than 1,200 girls – a third of whom were recruited from Kaiser medical centers in San Francisco, Oakland and San Rafael – since 2004. At the start of the study, the girls were between 6 and 8 years old.

Breast development at younger ages is a concern among physicians and parents because early menstruation, which can accompany it, has been linked to higher risk of breast cancer. Additional research has also found other potentially detrimental health, environmental and social impacts of precocious adolescence. Health experts say obesity is the biggest factor in the early onset of puberty, but the next step is to understand the factors that lead to obesity.

“It may not just be as simple as calories in and calories out,” said Janice Barlow, executive director of Zero Breast Cancer, a San Rafael group devoted to breast cancer prevention that Kaiser brought in to help with the study. “There may be other factors in environment that may be fueling the obesity epidemic.”

Barlow said the discoveries may help breast cancer research go beyond detection and treatment. “Being able to understand what influences the onset of puberty may open some windows for prevention,” she said.

Ethnic differences

The study, which was published Monday online in the medical journal Pediatrics, found some differences among ethnic groups. White participants, for instance, showed early stages of breast development at 9.7 years, about a year earlier than was noted in a landmark 1997 study of more than 17,000 girls nationwide.

The average age for black girls did not change significantly in the two studies, but remained at 8.8 years old. In the latest study, the median age was 9.3 years for Latinas and 9.7 years for Asian girls. Neither demographic was represented in the 1997 study.

Monday’s study showed that girls with high pediatric body mass index, a measurement used to assess a child’s physical growth in relation to other kids of the same age, started developing breasts earlier. White girls with very high BMIs – in the 85th percentile – developed almost two years earlier than normal-weight girls.

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