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Effect of ambient air pollution on development of childhood asthma Clark, Nina Annika


Asthma prevalence is increasing worldwide and the causes of this increase are largely unknown. There is increasing recognition of the importance of early environmental exposures in childhood asthma development. Outdoor air pollution has been shown to trigger asthma symptoms but its role in incident disease remains controversial. To address these questions, I investigated the effect of in utero and first year of life exposure to ambient air pollution on risk of asthma diagnosis in a nested case-control study. All children born in Southwestern British Columbia in 1999 and 2000 (N=37,401) were assessed for incidence of asthma diagnosis at age 3 - 4 years using hospitalization and primary physician records. Exposure to ambient air pollution was estimated for the gestational period and first year of life using high-resolution pollution surfaces derived from government monitoring station data as well as land use regression models adjusted for temporal variation. Conditional logistic regression analyses were used to estimate effects of CO, NO, NO₂, PM₁₀, PM₂.₅, O₃, SO₂, black carbon, wood smoke and proximity to roads and point sources on asthma diagnosis. Elevated risks of asthma diagnosis were observed with increased early life exposure to CO, NO, NO₂, PM₁₀, SO₂, black carbon and proximity to point sources. Effects were generally larger for first year exposures than in utero exposures, and larger for girls than boys. The results indicate that early life exposure to air pollution is associated with increased risk of asthma diagnosis in early childhood. Although the effect sizes are small, air pollution exposure in urban areas is ubiquitous so may have significant effects at the population level. These results should be confirmed when children are older and asthma diagnosis is more robust.

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