The relationship between low level nitrogen dioxide exposure and child lung function after cold air challenge

Background: Nitrogen dioxide (NO₂) or home gas appliance use has been inconsistently associated with adverse respiratory outcomes in childhood. Objectives: (i) To examine the contribution of home gas appliance type and personal NO₂ exposure. (ii) To examine the relationship between NO₂ exposure and child lung function and respiratory history. (iii) To assess whether these relationships vary by house dust mite sensitization status. Methods: A cross-sectional survey of 344 children (71% of the eligible group) with a mean age of 9.1 years from four randomly selected schools in the Australian Capital Territory from July to September 1999. Study measurements included a parental questionnaire, NO₂ exposure by passive gas samplers, skin prick testing for 10 aeroallergens and lung function at rest and after cold air challenge. Results: Total NO₂ exposure was low with a mean concentration of 10.1 ppb. No associations were found between NO₂ exposure or gas appliance use and asthma, wheeze or baseline lung function. Personal NO₂ exposure was associated with a reduction in forced expiratory volume in one second (FEV₁)/forced vital capacity (FVC) after cold air challenge (adjusted difference - 0.12% (- 0.23% to - 0.01%) per 1 ppb increase). After exclusion of children who had home heating changed because of asthma, gas heater use was also significantly associated with a reduction in this measure (adjusted difference - 2.0% (- 3.7% to - 0.2%)). There was some evidence that these reductions were greater among the non-mite-sensitized children. Conclusions: The effect of low-level NO₂ exposure on these respiratory outcomes was not marked. The possible effect of low-level NO₂ exposure on non-specific bronchial reactivity requires confirmation. Future studies on NO₂ and respiratory health should include measures of house dust mite sensitization and bronchial hyper-responsiveness.