Overweight and lower age at menarche: Evidence from the Italian HBSC cross-sectional survey 11 Medical and Health Sciences 1117 Public Health and Health Services

Background: A unique standardized national dataset on adolescent girls (21 regions) participating in the Italian Health Behaviour in School-aged Children Study (HBSC) was used to investigate the correlation between body mass index (BMI) and age at menarche. Methods: Two independent nationally representative survey datasets: one on 15-year-olds (n = 6907, in 21 regions, year 2013/2014) and one on 11-year-olds (n = 10,128, in 20 regions, year 2009/2010) were analysed. The survey instrument was a self-report questionnaire. Median age at menarche and 95% confidence intervals (CIs) were estimated by means of Kaplan-Meier analysis. Hierarchical models were used to assess the relationship between BMI and age at menarche (months). "Region-level obesity" was measured as the prevalence of overweight/obesity (%) in each region. Results: Region-level median age at menarche ranged between 12 years/3 months and 13 years/4 months. Region-level prevalence of overweight among 15-year-old girls ranged between 4 and 19%. Age at menarche was inversely associated with individual BMI (unstandardized regression coefficient beta = - 0.70; 95% CI, - 0.84 to - 0.56). Individual- and class-level measures of BMI accounted for 50% of the region-level variance in age at menarche. Conclusions: The results show that overweight in childhood is in relation with the early puberty in girls. Future surveys may take into account this report to clarify if overweight is the cause or consequence of early menarche.