Risk factors for wheezing in early adolescence: a prospective birth cohort study in Brazil.

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.