Abstract
Background: Exposure to air pollution in early life contributes to the burden of childhood asthma, but it is not clear whether lifetime exposure to air pollution can lead to asthma onset or progression in adulthood. We studied the effect of exposure to traffic-related air pollution over 35 years on the risk for hospitalization for asthma in elderly.
Methods: We followed 57 053 participants in the Danish Diet, Cancer and Health cohort, aged 50-65 years at baseline (1993-1997), for first hospital admission for asthma until 2006. Annual levels of nitrogen dioxide (NO2) were estimated at all residential addresses since 1971. We modelled the association between NO2 and hospitalization for asthma using Cox regression in people with and without previous hospitalizations for asthma, and assessed effect modification by co-morbid conditions.
Findings: During 9.9 years' mean follow-up, 977 of 53 695 eligible people (1.9%) were admitted to hospital for asthma: 821 (1.5%) admissions were among 53 143 people who had not and 176 (31.9%) among 552 people who had been hospitalized for asthma before baseline. NO2 levels were positively associated with risk for asthma hospitalization in the full cohort (hazard ratio and 95% confidence interval per inter-quartile range, 5.8 μg/m3: 1.12; 1.04-1.22), and in people without previous asthma hospitalization (1.10; 1.01-1.20), with the strongest effects for people with a history of asthma hospitalization (1.41; 1.15-2.07). Enhanced associations between NO2 and admissions for asthma were observed for people with COPD (1.30; 1.07-1.52).
Interpretation: Air pollution is a risk factor for progression and/or onset of asthma in late adulthood.
- © 2011 ERS
