Effect of air pollution on prevalence of chronic bronchitis symptoms-a cross-sectional analysis of 5 cohort studies

Background : Chronic bronchitis symptoms are associated with COPD and overall mortality. This study aims to assess effects of outdoor air pollution on prevalence of chronic bronchitis in five cohort studies (E3N, ECRHS, NSHD, SALIA, SAPALDIA) participating in the European Study of Cohorts for Air Pollution Effects (ESCAPE) project. Methods: Annual average concentrations of particulate matter (PM) and NO 2 /NO x and road traffic measures 2008-11, were assigned to home address at follow-up 2000-2011. Chronic bronchitis symptoms (³3 months for 2 or more years) were assessed as chronic cough and phlegm, chronic cough and chronic phlegm respectively. Cross-sectional multivariable logistic regression analyses were conducted at each cohort, adjusting for a confounder set common to all studies (age, sex, smoking, interview season, education) followed by random-effect meta-analysis. Results: 13,758 and 8784 participants respectively were included in NO 2 and PM analyses.No consistent associations were observed between any exposure and prevalence of chronic bronchitis.Combined effect estimates for chronic cough and phlegm were (shown as OR (95%CI) per10ug/m 3 ): NO 2 0.96 (0.89-1.04) and PM 10 0.85 (0.53-1.39).Corresponding results for never smokers were: NO 2 0.99 (0.84-1.18) and PM 10 1.34 (0.93-1.93).Similar null associations were seen for chronic cough alone or chronic phlegm. Conclusions: In contrast to some previously published European studies, this study did not find consistent effects of current air pollution exposures level on chronic bronchitis symptoms. Further investigations including use of back-extrapolated air pollution values to actual year of questionnaire are needed.