Relation of exposure to airway irritants in infancy to prevalence of bronchial hyper-responsiveness in schoolchildren

To find out whether exposure to sulphur dioxide during infancy is related to the prevalence of bronchial hyper-responsiveness (BHR), we studied schoolchildren (aged 7-13 years) from two areas of Norway—a valley containing a sulphur-dioxide-emitting aluminium smelter and a similar but non-industrialised valley. Bronchial responsiveness was assessed in 529 of the 620 participants. The median exposures to sulphur dioxide and fluoride were 37·1 μg/m3 and 4·4 μg/m3 at ages 0-12 months and 37·9 μg/m3 and 4·4 μg/m3 at 13-36 months. The risk of BHR increased with exposure to sulphur dioxide and fluoride at these ages; the odds ratio for a 10 μg/m3 increase in sulphur dioxide exposure at 0-12 months was 1·62 (95% Cl 1·11-2·35) and that for a 1 μg/m3 increase in fluoride exposure was 1·35 (1·07-1·70) at 0-12 months and 1·38 (1·05-1·82) at 13-36 months. Exposure to these low concentrations of airway irritants during early childhood is associated with an increased prevalence of BHR in schoolchildren.