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Résumé (anglais)

Highlights * Exposure to traffic related air pollution may affect childhood asthma onset timing. * We modelled NO2 exposure and asthma onset using survey data on Canadian children. * Children exposed to NO2 are more than twice as likely to have early onset asthma. * Risk is higher even when NO2 is well within World Health Organization guidelines. Abstract Although NO2, a major traffic related air pollutant, has been associated with onset of childhood asthma, young children may be more susceptible to traffic related air pollution exposure compared to other individuals. We linked data from National Longitudinal Survey of Children and Youths Cycle 1–5 (1994–2003) and the National Air Pollution Surveillance Program to determine the association between NO2 exposure and either early or late onset childhood asthma phenotypes. Children diagnosed with asthma from age 0–3 were defined as having early onset asthma. Children diagnosed with asthma from age 4–9 were defined as having late onset asthma. Mean NO2 exposure for each quartile was 6.31 ppb, 9.45 ppb, 11.83 ppb, and 17.9 ppb. Higher levels of NO2 exposure were more strongly associated with early childhood asthma (Quartile 3 OR: 2.11, 95% CI: 1.29, 3.44, Quartile 4 OR: 2.16, 95% CI: 1.27, 3.68) compared to the lowest level of NO2 exposure (Quartile 1). No such association was observed with risk of late childhood asthma onset. Asthma susceptibility to NO2 exposure may vary with the childhood developmental stage, and young children may be susceptible to NO2 exposure at levels well below national and international guidelines. Our study emphasizes the importance of considering the timing of childhood asthma onset in future studies and confirms the increased risk of early onset of childhood asthma associated even with relatively low NO2 exposure levels.