The role of exposure to ambient air pollution has been a topic of interest as a potential risk factor for respiratory symptoms and asthma. We expected that the prevalence rates would vary in Norway between the capital, Oslo, the mountainous area Hallingdal and the industrial area Odda. Surveys were conducted in school children, aged 6-16 years, in; Oslo (n = 2577), Hallingdal (n = 1177) and Odda (n = 831). The parent-reported prevalence of wheeze in past year was almost similar in Oslo (13.1 (95% CI 11.7-14.5)) and Upper Hallingdal (14.2 (13.1-15.3)), but lower in Odda (9.0 (7.0-11.0)). The findings for severe respiratory symptoms were almost equal. The age patterns within each area differed. The risk of wheeze ever (p < 0.001) and wheeze in past year (p = 0.04) decreased with increasing age in Odda, while there was an increase in the risk of exercise induced wheeze in Oslo (p = 0.02) and Hallingdal (p < 0.001). The lifetime prevalence of asthma was lowest in Odda (5.4 (3.8-7.0)) compared to Oslo (9.4 (8.2-10.6)) and Hallingdal (8.5 (6.8-10.2)). There was a positive association between physical activity and wheeze in past year. The results do not support the hypothesis that respiratory morbidity is more common in urban than rural areas, age and physical activity can influence the prevalence rates of respiratory symptoms in school children.

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The aim of this study was to assess prevalence of asthma and allergy in the non-polluted mountain area of Upper Hallingdal, Norway. All schoolchildren (7-16 years) who in a previous questionnaire survey (n = 1177) reported 'sometime' asthma were enrolled in group I (n = 80), the 59 who reported asthma-like symptoms in the past 12 months formed group II, and 77 of the healthy controls were randomly selected as group III. All 216 children underwent clinical examination, skin prick test, spirometry, bronchial provocation (PD20 metacholine) and treadmill exercise test. Subsequently they were reclassified as (1) healthy, never had asthma or symptoms, (2) symptoms not confirmed as asthma, (3) previous asthma, now healthy, (4) current asthma. Lifetime asthma prevalence was 10.2%. Based upon clinical examination, the specificity and sensitivity of the questionnaire for asthma diagnosis were 88 and 74%, respectively. Forced vital capacity was significantly higher among the asthmatics (group 4 versus 1), whereas forced expiratory volume in one second (FEV1) and forced expiratory flow at 50% of vital capacity were similar in all groups. More than 10% reduction in FEV1 following treadmill-run was found in 20% of children. Children with current asthma compared to controls had significantly; lower mean values of PD20 (9.1 versus 16.5 micromol), higher eosinophil cationic protein (13.4 versus 7.7 micromol) and more frequent sensitization to animal dander (56% versus 10%). In conclusion, despite a favorable climate, little mite sensitization and low outdoor pollution, asthma prevalence was surprisingly high in Upper Hallingdal. Sensitization to animal dander was the most important contributing factor for current asthma.