Alcohol promotes disease by altering oral bacteria

Drinking alcohol can heighten the risk of many ills, such as heart disease. But what are the harmful underlying mechanisms set in motion by alcohol consumption? One study shows that alcoholic drinks may drive changes in the mouth's microbiome that end up affecting the entire body.

Alcohol consumption is a risk factor for several diseases and conditions, such as cancer, heart disease, and — as it has recently been founddementia.

Some of the reasons why alcohol overuse can impair health are fairly straightforward.

For example, alcohol acts on receptors in the central nervous system that help to regulate blood pressure.

This can eventually produce an imbalance that may lead to hypertension. But drinking also impacts other sensitive biological mechanisms, which may, in turn, facilitate the body's vulnerability to disease.

Jiyoung Ahn and other researchers from the New York University School of Medicine in New York City have recently focused on how alcohol impacts the bacterial microbiome of the mouth.

Their findings, now published in the journal Microbiome, indicate that although a nightly drink may delight the palate, it will likely promote the growth of harmful bacteria in the mouth while at the same time stunting the development of helpful, probiotic bacteria.

"Our study offers clear evidence that drinking is bad for maintaining a healthy balance of microbes in the mouth and could help explain why drinking, like smoking, leads to bacterial changes already tied to cancer and chronic disease."

Jiyoung Ahn

More harmful bacteria, fewer helpful ones

The researchers worked with 1,044 adult participants, aged 55–87, who were based in the United States. All were recruited through the American Cancer Society (ACS) Cancer Prevention Study II and the National Cancer Institute (NCI) Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial.

All of the participants were healthy at the time of enrolment, and they provided samples of their oral bacteria as well as information about their drinking habits. Of them, 270 did not drink, 614 qualified as moderate drinkers, and 160 indulged in heavy drinking.

The researchers then analyzed the biological samples and combined these results with the data on the participants' drinking habits in order to understand which bacteria thrived in the oral microbiota of people who don't drink and those who do. They also explored which bacteria were prevented from developing.

Ahn and team found that alcohol consumption led to more consistent development of certain harmful bacteria in the mouth — namely, those belonging to the species Bacteroidales, Actinomyces, and Neisseria.

At the same time, healthy bacteria — such as those from the species Lactobacillales — that can help to prevent the certain diseases from taking hold could not develop properly in the oral microbiomes of drinkers.

"Drinkers," the study authors write, "had decreased abundance of order Lactobacillales [...] Other taxa [bacterial species], some of which are potentially pathogenic, were enriched with higher alcohol consumption."

Future research to investigate specific drinks

The abundance of harmful bacteria, as the researchers note, can lead to the development of heart diseases, as well as cancers of the head and neck and gastrointestinal cancer.

"Evidence indicates that oral microbiota dysbiosis [imbalance] is related to local oral diseases, such as periodontitis and dental caries and potentially to systemic diseases, including gastrointestinal cancers and cardiovascular disease," they explain.

Ahn suggests, therefore, that cutting down on the number of alcoholic drinks that we indulge in could help to reverse or even prevent the damage caused by unhealthy oral microbiota.

She also notes, however, that further research is now needed to understand how different types of alcoholic drinks independently influence the development of oral bacteria. Those who only drink wine, or only beer, or only strong liquors may have completely different oral microbiota.

"Future studies," the authors add, "should also investigate the impact of alcohol drinking on the metagenomic (functional) content of the oral microbiome."

"Improved understanding of the causes and health impacts of oral dysbiosis [bacterial imbalance] can lead to microbiome-targeted approaches for disease prevention," they conclude.