Smoking significantly changes the mouth’s microbiome, with potential implications for tooth decay and the ability to break down toxins, according to results published in the ISME (International Society for Microbial Ecology) Journal.
Smokers’ mouths have lower levels of the bacteria that break down smoking-related toxins.
Cigarette smoking is the number one cause of preventable disease and mortality in the US, leading to 480,000 deaths annually, or 20% of all deaths.
Over 16 million people live with a smoking-related illness in the US, according to figures from the Centers for Disease Control and Prevention (CDC).
In 2014, the CDC estimated that 16.8% of Americans aged 18 years and over were cigarette smokers or around 40 million adults.
Much recent research has focused on imbalances in the gut microbiota and how they relate to immune disorders such as Crohn’s disease and gastrointestinal cancers.
There are around 600 species of bacteria in the human mouth. Over 75% of oral cancers are thought to be linked to smoking, but it remains unclear whether microbial differences in the mouth affect the risk for cancer.
Researchers from New York University Langone Medical Center and its Laura and Isaac Perlmutter Cancer Center have been using precise genetic tests to investigate the impact of smoking on the composition and action of oral microbiota.
The team used mouthwash samples from 1,204 American adults who are registered in a large, ongoing study into cancer risk, funded by the National Institutes of Health (NIH) and the American Cancer Society (ACS).
Participants were all aged 50 years or over. Among them were 112 smokers and 521 individuals with no history of smoking. There were also 571 people who had quit smoking, 17% of them having stopped within the past 10 years.
Using genetic tests and statistical data, the researchers analysed the thousands of bacteria residing in the mouths of volunteers.
Results suggest that the oral microbiome of smokers is significantly different from that of people who have never smoked or are no longer smoking. In the mouths of smokers, the levels of 150 bacterial species were significantly higher, while levels of 70 other species were distinctly lower.
Proteobacteria made up 4.6% of overall bacteria in the mouths of smokers, compared with 11.7% in nonsmokers. Proteobacteria are thought to play a part in breaking down the toxic chemicals introduced by smoking.
By contrast, 10% more species of Streptococcus were found in the mouths of smokers, compared with nonsmokers. Streptococcus is known to promote tooth decay.
On quitting smoking, however, the oral microbiome appears to return to its previous state. In people who had smoked previously, but not in the last 10 years, the microbial balance was the same as in the mouths of nonsmokers.