Is the level of pollutants a risk factor for exercise-induced asthma prevalence?

Increased prevalence of asthma is commonly though to be associated with increased air pollution and with lifestyle changes. This study evaluates a possible relationship of levels of exposure to outdoor pollutants and exercise-induced asthma prevalence. Two groups of students (age 14-17) in distant urban areas were randomly selected (n = 649): Group I (n = 430), Vancouver, B.C., Canada; Group II (n = 219), Prague, Czech Republic. The free running asthma screening test was performed at both locations; self-report questionnaires were distributed to all participants. Peak expiratory flow rates were used to evaluate baseline and postexercise spirometry. A 15% decrease was considered a positive response to exercise challenge. The information on ambient air quality (SO2, NO2, O3, PM10) was obtained from appropriate institutions. Of 649 subjects tested [Group I: n = 430, F = 251 (58.4%,) M = 179 (41.6%) and Group II: n = 219, F = 112 (51.6%), M = 107 (48.4%)], 81 of the participants (13.2%) responded positively to the exercise challenge [Group I: n = 55 (12.8%) and Group II: n = 26 (11.8%)]. Of the population tested, 150 (23.6%) participants self-reported a history of allergic disease [Group I: 94 (21.9%) and Group II: 56 (25.6%)]. The levels of air pollutants obtained for Group II significantly exceeded those obtained for Group I. This study reports a prevalence of 12.3% of exercised-induced asthma among high school students, when free running asthma screening test and peak expiratory flow rate are used. Significantly different levels of common pollutants do not correlate with asthma prevalence. Although it is recognized that air pollution is a well-known asthma trigger, it cannot be a simple explanation for the continued problem of rising asthma prevalence.