Exposure to nitrogen dioxide and the occurrence of bronchial obstruction in children below 2 years

Background The objective of the investigation was to test the hypothesis that exposure to nitrogen dioxide (NO2) has a causal influence on the occurrence of bronchial obstruction in children below 2 years of age. Methods A nested case-control study with 153 one-to-one matched pairs was conducted within a cohort of 3754 children born in Oslo in 1992/93. Cases were children who developed ≥2 episodes of bronchial obstruction or one episode lasting >4 weeks. Controls were matched for date of birth. Exposure measurements were performed in the same 14-day period within matched pairs. The NO2 exposure was measured with personal samplers carried close to each child and by stationary samplers outdoors and indoors. Results Few children (4.6%) were exposed to levels of NO2 ≥30 μg/m3 (average concentration during a 14-day period). In the 153 matched pairs, the mean level of NO2 was 15.65 μg/m3 (± 0.60, SE) among cases and 15.37 (± 0.54) among controls (paired t = 0.38, P = 0.71). Conclusions The results suggest that NO2 exposure at levels observed in this study has no detectable effect on the risk of developing bronchial obstruction in children below 2 years of age.