Background: The association between smoking and inflammatory bowel disease has long been recognized, but its role in the development of microscopic colitis is less well defined. This systematic review and meta-analysis was conducted with the aims to identify all available studies on the association between smoking and risk of microscopic colitis and to synthesize their results.
Methods: The MEDLINE and EMBASE databases were searched from inception to May 2018 for cohort studies and case-control studies that compared the risk of microscopic colitis among current/former smokers vs individuals who have never smoked. Odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were extracted from the included studies and pooled together using a random-effects model, generic inverse variance method of DerSimonian and Laird. Between-study heterogeneity was quantified using the Q statistic and I2. Publication bias was assessed using funnel plots.
Results: Seven studies (2 cohort studies and 5 case-control studies) with 262,312 participants met the eligibility criteria and were included in the meta-analysis. Relative to never-smokers, current smokers had significantly increased odds of microscopic colitis, with a pooled OR of 2.99 (95% CI, 2.15-4.15; I2, 64%). Former smokers also had significantly higher odds of microscopic colitis compared with never-smokers, with a pooled OR of 1.63 (95% CI, 1.37-1.94; I2, 0%). Funnel plots were symmetric and did not provide suggestive evidence of publication bias for both analyses.
Conclusions: The current systematic review and meta-analysis found a significantly higher risk of microscopic colitis among current smokers compared with never-smokers. The risk attenuated among former smokers but remained significantly higher among never-smokers.
Keywords: cigarette smoking; meta-analysis; microscopic colitis.
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