Relationship between smoking status and ulcerative colitis: a meta-analysis based on a case-control study

Prior research has revealed an association between smoking, reduced ulcerative colitis (UC) risk, and improved disease severity among individuals with existing UC. Herein, we analysed the interaction between smoking habits and UC and its potential complexity, focusing on associations between smoking, incidence of UC, and therapeutic outcomes, via a meta-analysis of data from case-control studies. The PubMed, China Knowledge, WanFang, Web of Science, China Science and Technology Journal, Embase, and Scopus databases were searched, yielding nine case-control studies investigating the association between smoking and UC progression for inclusion. Compared to non-smoking or smoking cessation, smoking had a protective effect against UC, indicating that it may reduce the risk of developing UC; specifically, smoking was associated with a significant protective effect against UC compared to smoking cessation (pooled odds ratio (OR): 0.26, 95% confidence interval (CI): 0.21-0.32; P = 0.067, I² = 45.2%). Non-smoking was also protective compared with smoking cessation (pooled OR: 1.84, 95% CI 1.13-3.30; P = 0.935, I² = 0%). Further, smoking was significantly more protective than non-smoking (pooled OR: 0.48, 95% CI 0.40-0.56; P = 0.002, I² = 66.4%). These results indicate that smoking offers some protection against UC onset and may reduce disease severity in patients with existing UC.