title: Longitudinal changes in adiposity during adolescence: a population-based cohort.
abstract: OBJECTIVE
  We aimed to assess the trends in body mass index (BMI) and body fat percentage (BF%) from the age of 13 to 17 years and to evaluate how sociodemographic and behavioural characteristics at the age of 13  impact changes in BMI and BF%.
  
  
  METHODS
  Porto, Portugal.
  
  
  METHODS
  We evaluated 1451 adolescents in a community-based cohort.
  
  
  METHODS
  BMI z-scores were calculated according to CDC references. BF% was assessed by bioelectrical impedance. Variables with a significant effect in adiposity changes were identified through linear regression models. In girls, estimates were controlled for duration of follow-up, parental education, baseline BMI z-score, age at menarche and the interaction term baseline BMI z-score×age at menarche; in boys, adjustments were performed for duration of follow-up, parental education, baseline BMI z-score and the interaction term baseline BMI z-score×duration of follow-up.
  
  
  RESULTS
  On average, BMI z-score decreased from the age of 13 to 17 years (mean difference -0.20, 95% CI -0.23 to -0.16 among girls and -0.15, 95% CI -0.19 to -0.11 among boys). Accordingly, 12.4% of girls and 13% of boys moved to a lower BMI category and 2.2% of girls and 5.5% of boys to a higher category. There were sex differences in the significant determinants of adiposity trends. Among girls, BMI z-score significantly decreased with baseline BMI z-score (β=-0.163, 95% CI -0.204 to -0.122) and significantly increased with age at menarche (β=0.078, 95% CI 0.050 to 0.107). Results were similar for BF%. Among boys, BMI z-score significantly increased with higher parental BMI, and BF% decreased among those who wished to look larger at the age of 13 (β=-1.367, 95% CI -2.174 to -0.560), compared with those who were satisfied with their image.
  
  
  CONCLUSIONS
  In adolescents, ageing resulted in a decrease in BMI z-scores and BF%. BMI and BF% at the age of 13 were the major determinants of the observed trends. Our results suggest that adolescence is a possible specific time window for intervention.
authors.affiliation: Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal Cardiovascular Research and Development Unity, University of Porto Medical School, Porto, Portugal Institute of Public Health, University of Porto, Porto, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Araújo
authors.affiliation: Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal Cardiovascular Research and Development Unity, University of Porto Medical School, Porto, Portugal Institute of Public Health, University of Porto, Porto, Portugal.
authors.forename: Henrique
authors.initials: H
authors.lastname: Barros
authors.affiliation: Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal Cardiovascular Research and Development Unity, University of Porto Medical School, Porto, Portugal Institute of Public Health, University of Porto, Porto, Portugal.
authors.forename: Milton
authors.initials: M
authors.lastname: Severo
authors.affiliation: Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal Cardiovascular Research and Development Unity, University of Porto Medical School, Porto, Portugal Institute of Public Health, University of Porto, Porto, Portugal.
authors.forename: Carla
authors.initials: C
authors.lastname: Lopes
authors.affiliation: Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal Cardiovascular Research and Development Unity, University of Porto Medical School, Porto, Portugal Institute of Public Health, University of Porto, Porto, Portugal.
authors.forename: Elisabete
authors.initials: E
authors.lastname: Ramos
mesh_terms: D000273:Adipose Tissue; D050154:Adiposity; D000293:Adolescent; D000294:Adolescent Behavior; D000367:Age Factors; D015992:Body Mass Index; D005260:Female; D006801:Humans; D008297:Male; D011446:Prospective Studies; D012959:Socioeconomic Factors
keywords: Paediatrics; Public Health