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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