The multi-institutional study published in the journal Pediatrics confirms that girls of all races are beginning puberty at a younger age, a longstanding observation in the U.S.
“The impact of earlier maturation in girls has important clinical implications involving psychosocial and biologic outcomes,” said Frank Biro, M.D., lead investigator.
“The current study suggests clinicians may need to redefine the ages for both early and late maturation in girls.”
Researchers have observed that 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.
Experts say early maturation also results in greater risks of obesity, hypertension and several cancers — including breast, ovarian and endometrial cancer .
The study was conducted through the Breast Cancer and Environmental Research Program, established by the National Institute of Environmental Health Science.
Researchers at centers in the San Francisco Bay Area, Cincinnati and New York City examined the ages of 1,239 girls at the onset of breast development 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.
The girls were followed longitudinally, which involved multiple regular visits for each girl. Researchers said this method provided a good perspective of what happened to each girl and when it occurred.
Researchers found 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 — 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 for Hispanic girls in the study was 9.3 years, and 9.7 years for Asian girls.
Body mass index was a stronger predictor of earlier puberty than race or ethnicity.
Although the research team is still working to confirm the exact environmental and physiological factors behind the phenomenon, they conclude the earlier onset of puberty in white girls is likely caused by greater obesity.