title: Risk factors for wheezing in early adolescence: a prospective birth cohort study in Brazil.
abstract: BACKGROUND
  Many asthma studies are available in the literature, but few investigated whether risk factors for asthma differ by sex.
  
  
  OBJECTIVE
  To evaluate risk factors for wheezing in early adolescence, with emphasis on sex differences.
  
  
  METHODS
  A prospective birth cohort study was initiated in 1993; 87.5% of the original cohort was traced at 11 years, totaling 4,452 adolescents. Current wheezing was defined as at least 1 crisis in the previous 12 months. The following independent variables were analyzed: maternal smoking during pregnancy, wheezing at 4 years, maternal wheezing, and adolescent body mass index.
  
  
  RESULTS
  Current wheezing affected 13.5% (95% confidence interval [CI], 12.4%-14.5%) of the cohort. The prevalence of current wheezing was 15.3% (95% CI, 13.7%-16.8%) in boys and 11.7% (95% CI, 10.4%-13.1%) in girls (P < .001). Maternal smoking was related to an increased risk of wheezing for boys but not for girls. There was a significant tracking of wheezing from 4 to 11 years in both sexes, although the magnitude was stronger for boys. A dose-response association between maternal wheezing and adolescent wheezing was observed in boys but not in girls. Finally, obesity was associated with an increased risk of wheezing in boys but not in girls.
  
  
  CONCLUSIONS
  The variables explored in this investigation had a stronger effect on adolescent wheezing in boys than in girls. Public health strategies aimed at minimizing the burden of wheezing should take these sex differences into account.
authors.affiliation: Programa de Pós-graduação em Epidemiologia, Universidade Federal de Pelotas, Pelotas, Brazil. anamene@terra.com.br
authors.forename: Ana M B
authors.initials: AM
authors.lastname: Menezes
authors.forename: Pedro C
authors.initials: PC
authors.lastname: Hallal
authors.forename: Adriana
authors.initials: A
authors.lastname: Muiño
authors.forename: Moema
authors.initials: M
authors.lastname: Chatkin
authors.forename: Cora L P
authors.initials: CL
authors.lastname: Araújo
authors.forename: Fernando C
authors.initials: FC
authors.lastname: Barros
mesh_terms: D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000150:complications; D015995:Prevalence; D011446:Prospective Studies; D012135:Respiratory Sounds / Q000209:etiology*; D012307:Risk Factors; D012727:Sex Characteristics; D012907:Smoking / Q000009:adverse effects