Risk factors for bronchial hyperresponsiveness in teenagers differ with sex and atopic status

Background Sex-related differences in bronchial hyperresponsiveness (BHR) have been reported in adolescents, but the mechanisms remain obscure. Objective To investigate the risk factors for BHR in the Raine Study, a community-based longitudinal birth cohort. Methods At 14 years of age, children underwent a respiratory assessment including a questionnaire, lung function testing, methacholine challenge, and determination of atopic status. Results A total of 1779 children provided data for assessment, with 1510 completing lung function and methacholine challenge testing. Current asthma was present in 152 (10.4%), 762 (50.5%) were atopic, and 277 (18.6%) had BHR. BHR was more common in girls, whereas atopy was more common in boys, with no sex differences in asthma or current wheeze. Independent risk factors for BHR were being female (odds ratio [OR], 3.45; P < .001), atopy at 14 years (OR, 1.27; P = .004), and current asthma (OR, 2.15; P = .005). Better lung function was protective against BHR (forced expiratory flow between 25% and 75% of forced vital capacity/forced vital capacity, OR, 0.09; P < .001). Risk factors differed with sex and atopic status. Early-life factors were generally not independent risk factors for BHR at 14 years of age, with the exception of being smaller at birth in boys (birth length, OR, 6 × 10−9 ; P = .017) and maternal asthma in girls (OR, 1.84; P = .041). Current asthma was not a risk for BHR in nonatopic children. Conclusion Bronchial hyperresponsiveness was more common and more severe in girls. These differences could not be explained by differences in lung function or atopic status.