Association between smoking and risk of primary biliary cholangitis: A systematic review and meta-analysis

Background & Aims: Studies have suggested that smokers may have a higher risk of primary biliary cholangitis (PBC) although the results have been inconsistent. This systematic review and meta-analysis aim to better characterize the risk of PBC among smokers by identifying all relevant studies and summarizing their results together. Methods: A comprehensive literature review was conducted using Embase and Pubmed/MEDLINE databases from inception to September 2018 to identify all studies which compared the risk of PBC among current, ever and former smokers to non-smokers. Effect estimates from each study were extracted and combined together using the random-effect, generic inverse variance method of DerSimonian and Laird. Results: Nine case-control studies with 21,577 participants met the eligibility criteria and were included in the meta-analysis. The risk of PBC among ever smokers was significantly higher than non-smokers with the pooled odds ratio (OR) of 1.31 (95% CI, 1.03-1.67; I² 89%). Subgroup analysis found that the risk was higher in both former smokers (pooled OR 1.36; 95% CI, 1.01-1.84; I² 75%) and current smokers (pooled OR 1.18; 95% CI, 0.94-1.50; I² 79%), although the latter did not reach statistical significance. Immunomodulatory and cytotoxic effect of cigarettes were the possible mechanisms behind this increased risk. Conclusions: A significantly increased risk of PBC among individuals who ever smoked was observed in this study, adding to the already long list of harmful health consequences of smoking.