Puberty occurring at younger ages among white girls

Biro FM. Pediatrics.2010;126:e1-e8.

Since 1997, the percentage of 7-year-old white girls who reached pubertal maturation has nearly doubled, according to data from a recent study.

Data published in a 1997 issue of Pediatrics demonstrated that at age 7, 5% of white participants had reached breast stage >2. Recent results from a multicenter study demonstrate an increase in that statistic: 10.4% of white girls attained breast stage >2 at 7 years (P<.001). In addition, the proportion of black non-Hispanic girls who reached breast stage >2 by age 7 was also higher compared with the 1997 results (23.4% vs. 15.4%; P=.09).

As part of the National Institute of Environmental Health Science and National Cancer Institute’s Breast Center and the Environment Research Centers, researchers examined assessment methods and maturation status for a multisite cohort of girls as old as 8 years. Together, they developed a pubertal maturation assessment, which defined onset of maturation as breast stage 2.

The study enrolled 1,239 girls aged 6 to 8 years from East Harlem, the greater Cincinnati metropolitan area and the San Francisco Bay area. The researchers measured baseline characteristics by interviewing caregivers and taking anthropometric measurements. Using logistic regression, they identified factors associated with pubertal maturation; they used linear regression to study factors associated with height velocity.

According to the researchers, 10.4% of white girls, 23.4% of black non-Hispanic girls and 14.9% of Hispanic girls reached breast stage >2 by age 7. By age 8, 18.3% of white girls, 42.9% of black non-Hispanic girls and 30.9% of Hispanic girls had reached breast stage >2. A higher BMI percentile, older age, black race and being from the New York or Cincinnati site were all associated with breast stage >2, according to the logistic regression model. In addition, pubertal status was the strongest predictor for height velocity, according to the linear regression model (P<.0039); Asian race was the only other significant predictive factor (P=.017).

“The ability to capture with reasonable accuracy the timing and tempo of pubertal breast maturation in this prospective study … should allow us to pool data for detecting associations between specific factors, including diet and environmental chemicals, with variations in patterns of pubertal maturation,” the researchers wrote.

Though various racial/ethnic and socioeconomic statuses were represented, the researchers acknowledge that this is not a nationally represented sample. In addition, site-specific differences in maturation at baseline suggest varying dietary patterns, chemical exposures and racial/ethnic differences. Therefore, further examinations using longitudinal observations and more information on exposure and diet are needed, the researchers noted.

The study by Biro and colleagues is old wine in new skins. We have known for a long time that obesity will influence the advent of puberty. As obesity is more prevalent in minority children, the fact that they may have earlier thelarche is not surprising. As the pandemic of childhood obesity reaches white children, it is not surprising that they also have earlier thelarche. This may lead to prolonged estrogen exposure with its attendant possible effects on increasing the risk for breast cancer. Menarche, the key event in female puberty, has not changed at all; it is still at 12.8 years, on average, in normal-weight white children and a couple months earlier in minority children. Although this study is less flawed than the 1997 study by Herman-Giddens and colleagues (Pediatrics. 1997;99:505-512), it does not provide the much-needed correlation of breast development with BMI. Environmental chemicals have been postulated to have an effect in studies conducted in Denmark; however, no U.S. studies have identified any environmental causes, except the well-known 'golden double arches.' It would be difficult to conceive an environmental toxin that has racial predilection anyway. The more important clinical question is: What to do with the overweight girl who shows breast development at age 6? We still have to evaluate children of any race or weight who presents with breast development at age 6 or 7, lest we miss significant pathology such as endocrine or brain tumors, as the excellent study by Midyett and colleagues has shown (Pediatrics. 2003;111:47-51). We should steer clear from any racial profiling in pediatric endocrinology. Puberty at age 6 or 7 is not the new 'normal.'

– Paul Saenger, MD

Endocrine Today Editorial Board member

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