The Association Between Smoking and Both Types of Microscopic Colitis: A Systematic Review and Meta-Analysis

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Background and study aims: It has been suggested that smoking may be associated with microscopic colitis (MC) in some studies; however, there are conflicting results in the current literature with many of these studies having significant limitations. Our study aims to offer a meta-analysis evaluating the association between MC, including both its subtypes, and smoking. Patients and methods: A systemic review was conducted in PUBMED, Embase, PubMed Central, and ScienceDirect databases from inception through December 2019. Effect estimates from the individual studies were extracted and combined using the random effect, generic inverse variance method of DerSimonian and Laird and a pooled odds ratio (OR) was calculated. Forest plots were generated, and publication bias was assessed for using conventional techniques. Results: Eight observation studies with a total of 1461 patients with MC were included in this study, 383 of whom were active smokers (26.2%). Current smoking was significantly associated with MC (OR 3.58, 95% CI, 2.51–5.11), lymphocytic colitis (LC) (OR 3.64, 95% CI, 2.46–5.38), and collagenous colitis (CC) (OR 4.43, 95% CI, 2.68–7.32). Gender-specific subgroup analysis showed a significant association with smoking was found for CC in men (OR 4.53, 95% CI, 1.59–12.85), CC in women (OR 3.27, 95% CI, 2.35–4.54), LC in women (OR 2.27, 95% CI, 1.27–4.06) and MC in women (OR 2.93, 95% CI, 2.09–4.10). We found no publication bias as assessed by the funnel plots and Egger's regression asymmetry test. Conclusion: Our meta-analysis found a statistically significant association between smoking and both subtypes of MC.