1 Instituto Nutrición y Tecnología de los Alimentos, Universidad de Chile, Chile; 2 Instituto de Investigaciones Materno Infantil, Universidad de Chile, Chile; 3 División de Pediatría, Facultad de Medicina, Pontificia Universidad Católica de Chile, Chile.
Introduction: There is a secular trend in the decline of age at puberty onset in girls, but the evidence is controversial in the relation between adiposity and thelarche onset. Biro 2013 reported that Hispanics had thelarche onset at 9.3and there were differences by Body Mass Index (BMI) measured at 7y. Thus our aim is to assess if adiposity at different ages during childhood is related to age at thelarche onset in Chilean girls. Methods: This study includes 510 girls born in 2002-2003 who had thelarche onset by December 2014 and for whom we have every year anthropometry (weight, height) since birth until puberty onset. We estimated BMI z-score (BAZ; WHO 2007 standards); overweight was defined as 1-2 SD and obesity =2 SD. At age 7 a trained nutritionist evaluated appearance of breast bud via inspection and palpation every 6 months. Linear regression models were carried out to assess the relationship between BAZ and overweight/obesity and age at thelarche onset. Results: mean age of thelarche onset was 9.1+/-1.2 years. We did not observed associations between age at thelarche and BAZ from 0 to 4y; thereafter , BAZ was inversely related to age of thelarche onset(BAZ at 5y:ß=- 0.1, 95%CI:-0.2;-0.01; BAZ at 7y:ß=-0.1, 95%CI:-0.2;-0.03; BAZ 2y prior thelarche onset ß=-0.1, 95%CI:-0.2;-0.01; BAZ at age of thelarche onset: ß=-0.1, 95%CI:-0.2;-0.03). Overweight girls had earlier thelarche onset compared to normal counterparts; however no differences were observed in obese girls. Discussion: in Chilean girls age at thelarche is similar to Hispanics in USA. We observed inverse association between age at thelarche and BMI z-score as a continuous variable, but results were not consistent after categorizing the variable in overweight and obese. Further analyses are needed to better understand this association considering other markers of puberty onset and duration. (Funding FONDECYT:3130532/ 1120326, WCRF2010/245)