58 - Air Pollution and Risk of Inflammatory Bowel Diseases

Background: Temporal and geographic trends in inflammatory bowel disease (IBD) incidence reveal associations with industrialization and urbanization.Air pollution has been proposed as an environmental factor that might explain these associations; however, few studies have evaluated the relationship between ambient air pollution and IBD risk.Methods: We assessed associations between long-term exposure to atmospheric particulate matter and risk of incident Crohn's disease and ulcerative colitis among 117,408 participants in the Nurse's Health Study.We used sophisticated spatio-temporal models to predict residential address level monthly average ambient concentrations of particulate pollutants for participants living within in the contiguous United States from January 1988 to June 2006.We classified particulate matter based on aerodynamic diameter in µm (PM 2.5 , PM 10 and PM 2.5-10 ).We used Cox proportional hazards models to derive risk estimates while adjusting for multiple potential confounding factors including smoking, BMI, physical activity and measures of socioeconomic status.Results: In our analysis, encompassing over 1.86 million personyears of follow-up, we documented 151 incident cases of Crohn's disease and 145 cases of ulcerative colitis.We did not observe statistically significant associations between increasing 12-month average particulate concentrations and risk of ulcerative colitis (P>0.53 for all particle size categories).For Crohn's disease, however, we found inverse associations for all particle sizes. The hazard ratios for each 10 µg/m 3 increase in particulate concentrations were 0.59 (95% CI: 0.34-1.04)for PM 2.5 , 0.57 (95% CI: 0.33-0.98)for PM 10 , and 0.69 (95% CI: 0.50-0.95)for PM 2.5-10 .Conclusions: While our results for Crohn's disease are surprising, similar inverse associations for PM 10 exposure and Crohn's disease risk in adults have been reported previously in a population-based analysis conducted using a UK primary care database.Furthermore, in a case control study nested within the EPIC cohort, overall IBD risk appeared lower among those exposed to higher PM 10 concentrations.Further studies are required to identify whether there are biologic mechanisms that might explain this seemingly paradoxical association.Nonetheless, our data do not support the hypothesis that exposure to particulate air pollution increases the risk of developing IBD.