On the rising incidence of early breast development: puberty as an adaptive escape from ectopic adiposity in mismatch girls

Epidemiological observations have led to the hypothesis that the risk of developing some chronic noncommunicable diseases in adulthood is influenced not only by genetic and adult life-style factors but also by environmental factors acting in early life. Research in evolutionary biology, developmental biology, and animal and human physiology provides support for this idea and suggests that environmental processes influencing the propensity to disease in adulthood operate during the periconceptual, fetal, and infant phases of life. This "developmental origins of health and disease" concept may have important biological, medical, and socioeconomic implications.

Has the age at onset of thelarche in girls changed within the past 4 decades? This systematic review and meta-analysis found that age at pubertal onset, with thelarche assessed by physical or clinical examination of the breast, decreased by a mean of almost 3 months per decade from 1977 to 2013. In most textbooks, thelarche among girls younger than 8 years is considered pathologic and warrants further investigations; therefore, a younger age at thelarche in girls in the general population will change current diagnostic decision-making in girls suspected to have puberty disorders. The initial clinical sign of pubertal onset in girls is breast gland development (thelarche). Although numerous studies have used recalled age at menarche (first menstruation) to assess secular trends of pubertal timing, no systematic review has been conducted of secular trends of thelarche. To systematically evaluate published data on pubertal timing based on age at thelarche and evaluate the change in pubertal onset in healthy girls around the world. A systematic literature search was performed in PubMed and Embase of all original peer-reviewed articles published in English before June 20, 2019. Included studies used clinical assessment of breast development in healthy girls and used adequate statistical methods, including the reporting of SEs or CIs. The quality of the articles was evaluated by assessing study design, potential sources of bias, main characteristics of the study population, and methods of statistical analysis. In accordance with PRISMA guidelines, all articles were assessed for eligibility independently by 2 authors. Weighted regression analysis was performed using a random-effects model. Studies examining age at thelarche (development of Tanner breast stage 2) in healthy girls. The literature search resulted in a total of 3602 studies, of which 30 studies fulfilled the eligibility criteria. There was a secular trend in ages at thelarche according to race/ethnicity and geography. Overall, the age at thelarche decreased 0.24 years (95% CI, −0.44 to −0.04) (almost 3 months) per decade from 1977 to 2013 ( P  = .02). The age at thelarche has decreased a mean of almost 3 months per decade from 1977 to 2013. A younger age at pubertal onset may change current diagnostic decision-making. The medical community needs current and relevant data to redefine “precocious puberty,” because the traditional definition may be outdated, at least in some regions of the world. This systematic review and meta-analysis evaluates published data on pubertal timing based on age at thelarche and evaluates the change in pubertal onset in healthy girls around the world.

The objective of this study was to determine the influence of birth weight and postnatal weight gain on age at menarche. This was a prospective cohort study where girls from the West Australian Pregnancy (Raine) Cohort Study were followed prospectively from fetal life (18 wk of pregnancy) to adolescence (12-14 yr). Age at menarche was the main outcome measure. Growth status at birth was judged by expected birth weight ratio (EBW; a ratio of observed infant's birth weight over median birth weight appropriate for maternal age, weight, height, parity, infant sex, and gestational age). Postnatal growth status was judged by body mass index (BMI). Both EBW (P = 0.020) and BMI in childhood (8 yr of age) (P < 0.001) were associated with age at menarche. Menarche occurred earlier in girls with lower EBW and higher BMI. We have demonstrated for the first time that both birth weight and weight gain in childhood are associated with age at menarche. Weight gain before birth and subsequent weight gain up to the age of 8 yr were found to have opposing influences on the timing of menarche. Lower EBW combined with higher BMI during childhood predicted early age at menarche, and this relationship existed across normal birth weight and BMI ranges.