New U.S. research has found that just one alcoholic drink a day could change the mouth's microbiome and increase the number of oral bacteria, which have previously been linked to an increased risk of certain cancers.

Led by researchers at NYU School of Medicine, the study looked at 1,044 participants between the ages of 55 and 87 who were all healthy at the start of the study.

Participants were asked to provide mouthwash samples of their oral microbiome, as well as information about their alcohol consumption.

Moderate drinkers were defined as those who drink one drink per day on average for women, and one to two drinks per day on average for men. Women and men who had greater than one or two drinks per day, respectively, were considered heavy drinkers. 

The team then used laboratory testing to genetically sort and quantify the oral bacteria among the participants.

The results showed that moderate and heavy drinkers had more of the potentially harmful Bacteroidales, Actinomyces, and Neisseria species of bacteria, and fewer Lactobacillales, bacteria commonly used in probiotic food supplements intended to prevent sickness, than non-drinkers.

Senior investigator Jiyoung Ahn, PhD, commented on the findings saying, "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." 

Cancers that have already been linked to changes in oral bacteria include head and neck cancers and gastrointestinal cancers. The oral microbiome has also been linked to the risk of periodontal disease.

However, the team noted that further research is needed to see how these alcohol-related changes could be linked to various diseases.

The researchers also added that although the study was large enough to look at the differences in bacteria between drinkers and non-drinkers, more participants would be needed to assess any bacterial changes between drinkers of different types of alcohol. For example, only 101 wine-only drinkers were included in the study, along with just 39 who drank only beer, and 26 who drank only liquor.

Ahn also explained that changes in the microbiome could be caused by the acids in alcoholic drinks, which may make the oral environment hostile for certain bacteria to grow. Another explanation is that the harmful byproducts released when alcohol breaks down could build up in the mouth, including chemicals called acetaldehydes, which are produced by certain bacteria, such as Neisseria.

The results of the study can be found online in the journal Microbiome.