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Kicking the habit: Oral microbiota bounces back five years after quitting smoking

In a recent study published within the journal Scientific Reports, researchers examined the changes in oral microbiota composition as a result of smoking.



Smoking is a risk factor for cardiovascular diseases, oropharyngeal cancers, periodontitis, and respiratory diseases, amongst others. Oral microbiota alterations have been reported in smokers and cases of periodontitis, cardiovascular diseases, and squamous cell carcinoma. Thus, smoking-related oral microbiota changes may contribute to chronic conditions. Oral microbiota has several functions and is involved within the nitrate reduction pathway.

Study: Smoking and salivary microbiota: a cross-sectional evaluation of an Italian alpine population. Image Credit: Lightspring / Shutterstock

Nitrate-rich diets elevate the abundance of nitrate-reducing bacteria (NRB). Whether tobacco modifies the relative abundance of NRB stays unclear. The composition of the salivary microbiota varies by smoking behavior. A meta-analysis noted that smokers had increased Actinobacteria, lower Proteobacteria, and reduced proportion of aerobes in comparison with never or former smokers.

Although associations between salivary microbiota composition and smoking status have been characterised in American populations, no study has examined the associations between salivary microbiota and metabolic potential with years since smoking cessation or smoking intensity in Europeans.

The study and findings

The current study investigated associations between salivary microbiota composition and smoking status, history, and intensity in an Italian cohort of 1,601 individuals. Participants were aged 45, on average, with nearly 53% of the cohort being female. Most subjects (72%) had ≥ 20 natural teeth, and 45% were former or current smokers. The first tobacco source was cigarettes for all except five individuals.

Former and current smokers aged 41-60 with the next cumulative smoking exposure had fewer teeth than those with lower exposure. DNA sequencing of oral microbiota from select samples yielded nearly 36 million reads, with 22,308 median reads per sample. The dataset contained 627 amplicon sequence variants from 82 genera. Firmicutes and Prevotella were probably the most dominant on the phylum and genus levels, respectively, within the cohort.

The microbiota composition was related to smoking, age group, sex, and variety of teeth. There was no significant association between alpha diversity and smoking status. Former and never smokers had highly similar microbiota composition. Forty-four genera significantly differed between never and current smokers, adjusted for the variety of teeth, sex, and age.

Further, the relative abundance of aerobes was consistently reduced in smokers in favor of anaerobes. Next, the team found a positive association between Fretibacterium and increases in day by day smoking intensity (grams of tobacco per day). Furthermore, nine genera were differentially abundant between current and never smokers.

The typical relative abundance of aerobic taxa significantly reduced with increasing smoking intensity, adjusted for variety of teeth, age, and sex, whereas that of anaerobes increased barely. Besides, the researchers explored associations between the microbiota of former smokers and years since quitting.

The microbiota profile of participants who quit smoking ≥ five years ago was more prone to resemble that of never smokers. The relative abundance of aerobic taxa showed a gentle increase within the 20 years since quitting smoking. Finally, there have been 21 differentially abundant pathways between never and current smokers.

Conclusions

To summarize, the study explored associations of salivary microbiota composition with smoking status, intensity, and years since quitting in an Italian cohort. Aerobes varied by the intensity and frequency of smoking exposure. Further, the salivary microbiota composition was generally similar between former and never smokers, particularly amongst those that quit smoking greater than five years ago.

Multiple aerobic microbial pathways were reduced in smokers, including the ubiquinol synthesis and nitrate reduction pathways. Moreover, pathways requiring oxygen or those generating an excess reducing power were reduced, suggesting that smoking ends in a hypoxic environment within the oral cavity. The lower abundance nitrate reduction pathway in smokers may also explain the effect of smoking on the chance of periodontal and cardiovascular diseases, which needs to be tested in future studies.

The study’s limitations are the cross-sectional design and the shortage of assessment of gum health or the variety of missing, filled, or decayed teeth. Furthermore, residual confounding was possible despite controlling for the variety of teeth, sex, and age as a result of alcohol intake, eating regimen, and drugs usage. Taken together, the study revealed an association between salivary microbiota changes and smoking. Aerobic taxa were probably the most sensitive to exposure to smoke, whatever the phylogeny. Individuals who quit smoking five years ago had microbiota profiles much like those of never-smokers.

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