NO2, as a marker of air pollution, and recurrent wheezing in children: a nested case-control study within the BAMSE birth cohort

Aims: To investigate the association between air pollution, including with NO₂, and recurrent wheezing during the first two years of life.

Methods: A birth cohort (BAMSE) comprised 4089 children, for whom information on exposures, symptoms, and diseases was available from parental questionnaires at ages 2 months, and 1 and 2 years. NO₂ was measured during four weeks in and outside the dwellings of children with recurrent wheezing and two age matched controls, in a nested case-control study (540 children).

Results: Conditional logistic regression showed an OR of 1.60 (95% CI 0.78 to 3.26) among children in the highest quartile of outdoor NO₂ exposure in relation to those in the lowest quartile, adjusted for potential confounders. The corresponding OR for indoor NO₂ was 1.51 (95% CI 0.81 to 2.82). An interaction with environmental tobacco smoke (ETS) was indicated with an OR of 3.10 (95% CI 1.32 to 7.30) among children exposed to the highest quartile of indoor NO₂ and ETS. The association between NO₂ and recurrent wheezing appeared stronger in children who did not fulfil the criteria for recurrent wheezing until their second year.

Conclusions: Although the odds of increased recurrent wheezing are not statistically significantly different from one, results suggest that exposure to air pollution including NO₂, particularly in combination with exposure to ETS, increases the risk of recurrent wheezing in children.