Press Release

New research in Pediatrics shows that obesity is the largest predictor of earlier onset puberty in girls, a phenomenon that is affecting white girls at younger ages than previously reported.

Published online Nov. 3, the multi-institutional study strengthens a growing body of research documenting the earlier onset of puberty in girls of all races.

Researchers at centers including Kaiser Permanente in the San Francisco Bay Area, as well as sites in Cincinnati and New York City, examined the ages at the onset of breast development of 1,239 girls, and the impact of body mass index and race/ethnicity. The girls ranged in age from 6 to 8 years at enrollment and were followed at regular intervals from 2004 to 2011. Researchers used well-established criteria of pubertal maturation, including the five stages of breast development known as the Tanner Breast Stages.

In this longitudinal study, we confirmed that the age and onset of puberty does seem to be occurring earlier than was found in previous observational studies, said Lawrence H. Kushi, ScD, a study co-author and principal investigator for the San Francisco Bay Area study center, known as the Cohort study of Young GirlsNutrition, Environment, and Transitions (CYGNET).

Girls with earlier maturation are at risk for a multitude of challenges, including lower self-esteem, higher rates of depression, norm-breaking behaviors and lower academic achievement. Early maturation also results in greater risks of obesity, hypertension and several cancers

The San Francisco Bay Area cohort included 444 girls recruited from Kaiser Permanente medical centers in Oakland, San Francisco and Marin County, with an average age of 7.4 years old at the time of enrollment; 22% of the girls were black, 12% Asian, 24% Hispanic and 42% white.

The girls were followed longitudinally, which involved multiple annual visits for each girl. Researchers said this method provides a good perspective on what happened to each girl and when it occurred.

Researchers found that the respective ages at the onset of breast development varied by race, body mass index (obesity) and geographic location. Breast development began in white non-Hispanic girls at a median age of 9.7 years, nearly a year earlier than previously reported. Black girls continue to experience breast development earlier than white girls, at a median age of 8.8 years. The median age was 9.3 years for Hispanic girls and 9.7 years for Asian girls in the study.

Body mass index was a stronger predictor of earlier puberty than race or ethnicity. Although the research team is still working to identify other environmental and physiological factors behind the phenomenon, they conclude that the earlier onset of puberty in white girls is likely caused by higher rates of obesity.

“The obesity epidemic is causing real changes in kids’ development,” said Louise C. Greenspan, MD, a study co-author and pediatric endocrinologist with Kaiser Permanente San Francisco.

The study was conducted through the Breast Cancer and Environment Research Program, established by the National Institute of Environmental Health Sciences and the National Cancer Institute. The lead author is Frank Biro, MD, of Cincinnati Children. Pediatrics is the journal of the American Academy of Pediatrics.

Funding support for the study came from the Breast Cancer and the Environment Research Program of the National Institute of Environmental Health Sciences and the National Cancer Institute, with additional support from other grants from the National Institute of Environmental Health Sciences, the National Center for Research Resources, and the Avon Foundation.