Background: Conclusive data on the risk factors that modify bronchial hyperresponsiveness after airway exposure to modulating triggers (histamine, methacholine and exercise) are lacking. In recent years some risk factors such as air pollution or infection have been questioned and even considered protective.
Objectives: To assess the prevalence of bronchial hyperresponsiveness to exercise among schoolchildren and its association with different risk factors.
Methods: Three thousand thirty-three schoolchildren aged 13-14 years were studied. Participants answered a questionnaire on respiratory symptoms. A total of 2,842 children underwent exercise challenge testing for bronchial hyperresponsiveness. This study was part of the International Study of Asthma and Allergies in Childhood (ISAAC).
Results: A fall in peak expiratory flow rate of (15 % after exercise was found in 324 children (11.4 %), of whom 29 (9 %) also presented symptoms of asthma. Bronchial hyperresponsiveness to exercise was significantly associated with lower age, female sex, high socioeconomic level and attending a private school. No association was found between bronchial hyperresponsiveness and obesity, tobacco or viral infections.
Conclusions: These findings are not completely consistent with those of other studies, suggesting that local environmental factors may influence the prevalence of bronchial hyperresponsiveness. Further studies are required to clarify these conflicting data.