There is growing evidence of pubertal maturation occurring at earlier ages, with many studies based on cross-sectional observations. This study examined age at onset of breast development (thelarche), and the impact of BMI and race/ethnicity, in the 3 puberty study sites of the Breast Cancer and the Environment Research Program, a prospective cohort of >1200 girls.
Girls, 6 to 8 years at enrollment, were followed longitudinally at regular intervals from 2004 to 2011 in 3 geographic areas: the San Francisco Bay Area, Greater Cincinnati, and New York City. Sexual maturity assessment using Tanner staging was conducted by using standardized observation and palpation methods by trained and certified staff. Kaplan-Meier analyses were used to describe age at onset of breast maturation by covariates.
The age at onset of breast stage 2 varied by race/ethnicity, BMI at baseline, and site. Median age at onset of breast stage 2 was 8.8, 9.3, 9.7, and 9.7 years for African American, Hispanic, white non-Hispanic, and Asian participants, respectively. Girls with greater BMI reached breast stage 2 at younger ages. Age-specific and standardized prevalence of breast maturation was contrasted to observations in 2 large cross-sectional studies conducted 10 to 20 years earlier (Pediatric Research in Office Settings and National Health and Nutrition Examination Survey III) and found to have occurred earlier among white, non-Hispanic, but not African American girls.
We observed the onset of thelarche at younger ages than previously documented, with important differences associated with race/ethnicity and BMI, confirming and extending patterns seen previously. These findings are consistent with temporal changes in BMI.
Comments
Earlier Onset of Breast Development Does Not Necessarily Mean Earlier Onset of Puberty
The authors of the publication "Onset of Breast Development in a Longitudinal Cohort" are to be commended for a carefully conducted and analyzed study verifying earlier appearance of breast development, associated with both race/ethnicity and BMI.
These data have been interpreted to mean that puberty itself is starting earlier and this unverified concept has led to inappropriate referrals for precocious puberty and other non indicated medical costs. Such referrals are often driven by the parents' perception that their daughters will have early menarche. But there is no evidence that this early onset of breast development is being followed by an earlier onset of menarche. Earlier onset of puberty (activation of hypothalamic-pituitary ovarian axis-HPO) would result in an earlier age of menarche, however the age of menarche has changed only minimally over the last several decades.
The age of breast development was estimated from the interval first observation and the previous visit, because of longitudinal data, interval -censoring data was used rather than the usual survival methods used for previously published cross-sectional data. This alone may have lowered the apparent age of breast development since this method differs from most previous studies.
As with previous such reports, the media has cited this as evidence of earlier onset of puberty, rather than simply an earlier physical appearance of breast development. It is then crucial that the medical community and the general public be aware that earlier appearance of breast development does not necessarily indicate an earlier onset of puberty. We have observed such minimal breast development in 7 year-old girls with no further progression over 3 subsequent years. Current evidence suggests that the stimulation for this minimal, non-progressive breast development is an increased estrogen effect independent of a pubertal HPO axis.
The authors mention that this earlier onset of breast development does not indicate pubertal HPO axis activation without further documentation. Such documentation would involve hormonal verification or at least progression of breast development. This is true both for those girls with fullness or puffiness in the area of the nipples and those with a palpable breast bud. We would encourage the authors to investigate the cause of early development and rate of progression.
In the meantime, assessment of such patients involves determination of breast tissue by inspection and palpation followed by careful clinical observation for progression. Finally, perhaps it would be better to state "early appearance" than onset of breast development since the later implies the beginning of an ongoing process.
Conflict of Interest:
None declared