Impact of cigarette smoking on gut microbial dysbiosis: a structured literature review

The gut microbiota (GM) comprises microorganisms in the human gastrointestinal tract (GIT). Lifestyle choices like smoking lead to gut dysbiosis. This review assessed the effect of cigarette smoke (CS) on gut microbial dysbiosis (GMD) in active smokers compared to non-smokers, as well as the resulting public health implications. A comprehensive search was conducted using the Cumulative Index to Nursing and Allied Health Literature (CINAHL), Medline, and PubMed. The search result was reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. The Critical Appraisal Skills Programme (CASP) tool was used to evaluate the recruited studies. There were 468 articles found, with 17 of them qualifying for full-text screening. Five of these studies were included in the review. Smoke harmed gut microbe proportions; smokers had more Bacteroidetes and less Firmicutes than non-smokers, affecting their Firmicutes/Bacteroidetes (Fir/Bac) ratio. This has significant public health implications. Organisms enriched in the smokers such as Bacteroidales eggerthii (B. eggerthii), Bacteroidales bacterium (B. bacterium) pH 8, Ruminococcus bromii (R. bromii), and Ruminococcus albus (R. albus) were found to be positively correlated with inflammatory biomarkers. Other organisms, such as Eubacterium eligens (E. eligens), Eubacterium ramulus (E. ramulus), Eubacterium rectale (E. rectale), Eubacterium ventriosum (E. ventriosum), Roseburia hominis (R. hominis), Ruminococcus torques (R. torques), and Roseburia inulinivorans (R. inulinivorans), were negatively correlated with inflammatory markers and were more in non-smokers.