The Effect of Cigarette and Alcohol on Intestinal Flora: A Population-Based Cross-Sectional Study

Background: Human intestinal flora is affected by the exogenous microenvironment. This study aims to figure out the effect of cigarette and alcohol drinking on gut microbiota in health adults. Methods: 170 health subjects were enrolled and divided into four groups including none smokers and drinkers (group A), smokers (group B), drinkers (group C), and smokers and drinkers (group D). Fecal samples were collected and sequenced by 16S rRNA to analyze the microbial composition and KEGG predicted functional pathways. Short chain fatty acids (SCFAs) levels in feces were determined by gas chromatography. Findings: We observed lower diversity and evenness indicated by Simpson and Heip indexes in smokers or drinkers when compared as control group A (p<0.05). The smokers only group had lower diversity and evenness compared with group C and group D (p＜0.01 and p＜0.05, respectively). The overall bacterial profiles had no difference among different groups. Smokers only (group B) or both smokers and drinkers (group D) showed significant increase of phylum Bacteroidetes, as well as higher Bacteroidetes: Firmicutes ratio by nearly 3- and 2- fold change respectively compared with group A(p<0.05). In contrast, the abundance of ‘beneficial’ bacteria, including butyric-producing bacteria Ruminococcaceae_UCG-005, Flavonifractor and Bacillus was significantly decreased in smoker or drinker populations, especially in smokers. We found that immunity-related, bacterial metabolism and disease-associated pathways were more abundant in group smoker or drinker populations. There is no difference in SCFAs among all groups. Interpretation: Human intestinal flora was affected by cigarette and alcohol, especially by cigarette in microbial diversity and composition. Our results indicated that the intestinal flora played potential role in cigarette/alcohol-related diseases. However, when two factors considered, the effect on the intestinal flora and diseases maybe counteract by each other. Funding Statement: This work was supported by the Public Welfare Technology Application Research Plan of Zhejiang Province for Laboratory Animals (2017C37149), Science and Technology Plan of Medicine and Health of Zhejiang Province (2018KY474), Natural Science Foundation of Zhejiang Province (LY18H160011). Declaration of Interests: All authors claim that there is no competing interest between them. Ethics Approval Statement: This study was conducted under the guide of Ethics Committee of Sir Run Run Shaw Hospital and the China Association for Clinical Research.