Effects of Smoking and Smoking Cessation on the Intestinal Microbiota

Introduction We evaluated associations of smoking heaviness markers and the effects of smoking cessation on the intestinal microbiota and cardiovascular disease risk factors in current smokers undertaking a quit attempt. Methods and Results Participants were current smokers enrolled in a randomized clinical trial of smoking cessation therapies with visits, risk factor measurements, and fecal collections at baseline, 2, and 12 weeks after starting a quit attempt. Genomic DNA was extracted from fecal samples followed by 16S rRNA gene sequencing and analysis using the QIIME2 software workflow. Relative abundances of bacterial taxa and alpha- and beta-diversity measures were compared. Longitudinal changes in bacterial taxa abundances were compared using analysis of covariance (ANCOVA). The 36 smokers were (mean [standard deviation]) 51.5 (11.1) years old (42% male) and smoked 15.1 (6.4) cigarettes per day for 22.7 (11.9) pack-years. Their exhaled carbon monoxide (CO) levels were 17.6 (9.3) ppm. At baseline, relative abundances of the phylum Actinobacteria were correlated inversely with pack-years (rho=-0.44, p=0.008) and Cyanobacteria were correlated positively with CO levels (rho=0.39, p=0.021). After 12 weeks, abundances of the phyla Bacteroidetes increased (p ANCOVA =0.048) and Firmicutes decreased (p ANCOVA =0.036) among abstainers compared to continuing smokers. Increases in alpha-diversity were associated with lower heart rates (rho=-0.59, p=0.037), systolic blood pressures (rho=-0.58, p=0.043), and C-reactive protein levels (rho=-0.60, p=0.034). Conclusions Smoking cessation leads to minor changes in the intestinal microbiota. It is unclear if the proven health benefits of smoking cessation lead to salutary changes in the intestinal microbiota and if such changes affect cardiovascular disease risk. Implications In the largest prospective study of current smokers making a quit attempt to date, we showed that smoking cessation has minor effects on the composition of the gut microbiome. In successful abstainers, relative abundances of the phyla Bacteroidetes increased and Firmicutes decreased, a pattern of uncertain clinical significance. We did not observe significant changes in alpha- or beta-diversity with smoking cessation. It is unclear if the proven health benefits of smoking cessation lead to salutary changes in the intestinal microbiota and if such changes affect cardiovascular disease risk.