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Passive Smoking and Inflammatory Bowel Disease: A Meta-Analysis

OBJECTIVES:Active smoking has a well-documented role in the etiology of inflammatory bowel disease (IBD), but the role of passive smoking has been unclear. This meta-analysis examined the relationship between prenatal smoke exposure and childhood passive smoke exposure and the development of IBD.METHODS:We searched the MEDLINE and EMBASE databases to identify observational studies regarding the relationship between prenatal and/or childhood passive smoke exposure and the development of Crohn's disease (CD) and/or ulcerative colitis (UC). Pooled odds ratios (OR) were calculated for each relationship.RESULTS:A total of 534 and 699 potential studies were identified from the MEDLINE and EMBASE databases, respectively, of which 13 met all of our inclusion criteria. Overall, we did not observe a positive relationship between childhood passive smoke exposure and CD (OR 1.10, 95% confidence interval [CI] 0.92–1.30) or UC (OR 1.01, 95% CI 0.85–1.20). Likewise, we did not observe an association between prenatal smoke exposure and CD (OR 1.10, 95% CI 0.67–1.80), or prenatal smoke exposure and UC (OR 1.11, 95% CI 0.63–1.97).CONCLUSIONS:Our meta-analysis suggests that there is not a strong association between childhood passive smoke exposure and the development of CD. We found no evidence that childhood passive smoke exposure exerts a protective effect against UC, as is the case in active smoke exposure. The heterogeneity among the small number of studies limited the ability to draw conclusions about prenatal smoke exposure.