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Introduction: Environmental factors related to urbanization and industrialization are believed to be involved in inflammatory bowel disease (IBD) development, but no study has looked at the association between greenspace and IBD., Methods: We conducted a retrospective cohort study using linked population-based health administrative and environmental data sets. The study population comprised 2,715,318 mother-infant pairs from hospital births in Ontario, Canada, between April 1, 1991, and March 31, 2014. We measured the exposure to residential greenspace using the normalized difference vegetation index derived using remote-sensing methods. Average greenspace was estimated for the pregnancy and childhood periods. We used mixed-effects Cox proportional hazard models to assess potential associations between residential greenspace and the risk of developing IBD before 18 years while adjusting for covariates including sex, maternal IBD, rural/urban residence at birth, and neighborhood income., Results: There were 3,444 IBD diagnoses that occurred during follow-up. An increase in the interquartile range of residential greenspace during the childhood period was associated with a lower risk of developing pediatric-onset IBD (hazard ratio [HR] 0.77, 95% confidence interval [CI] 0.74-0.81). This relationship was significant for both ulcerative colitis (HR 0.72 95% CI 0.67-0.78) and Crohn's disease (HR 0.81, 95% CI 0.76-0.87). There was a linear dose response across increasing quartiles of greenspace (P < 0.0001). No consistent association was detected between maternal intrapartum greenspace exposure and pediatric-onset IBD., Discussion: Higher exposure to residential greenspace during childhood was associated with a reduced risk of IBD, suggesting a novel avenue to prevent IBD in children., (Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of The American College of Gastroenterology.) more...