There is growing evidence that asthma symptoms can be aggravated or events triggered by exposure to indoor nitrogen dioxide (NO(2)) emitted from unflued gas heating. The impact of NO(2) on the respiratory health of children with asthma was explored as a secondary analysis of a randomised community trial, involving 409 households during the winter period in 2006 (June to September). Geometric mean indoor NO(2) levels were 11.4 μg · m(-3), while outdoor NO(2) levels were 7.4 μg · m(-3). Higher indoor NO(2) levels (per logged unit increase) were associated with greater daily reports of lower (mean ratio 14, 95% CI 1.12-1.16) and upper respiratory tract symptoms (mean ratio 1.03, 95% CI 1.00-1.05), more frequent cough and wheeze, and more frequent reliever use during the day, but had no effect on preventer use. Higher indoor NO(2) levels (per logged unit increase) were associated with a decrease in morning (-17.25 mL, 95% CI -27.63- -6.68) and evening (-13.21, 95% CI -26.03- -0.38) forced expiratory volume in 1 s readings. Outdoor NO(2) was not associated with respiratory tract symptoms, asthma symptoms, medication use or lung function measurements. These findings indicate that reducing NO(2) exposure indoors is important in improving the respiratory health of children with asthma.
Trial registration: ClinicalTrials.gov NCT00489762.