From morning coffee and tea to beer, wine, and fruit juice, researchers examined how everyday drinking habits relate to the complex bacterial communities living in our mouths.
Study: Associations between commonly consumed beverages and the oral microbiome in three US cohort studies. Image Credit: Stockah / Shutterstock
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
In a recent study posted to the medRxiv preprint* server, researchers evaluated associations between commonly consumed beverages and the oral microbiome. The analysis pooled data from three large United States prospective cohorts (total sample n = 5,598) and examined relationships between habitual beverage intake and oral microbial diversity and composition.
The results suggest that alcohol consumption was more strongly associated with differences in the oral microbiome than the other beverages examined. Higher alcohol intake was associated with greater overall bacterial richness and increased occurrence of certain bacterial genera linked to periodontal disease. Coffee showed a few significant genus-level associations, while tea, sugar-sweetened beverages (SSBs), artificially sweetened beverages (ASBs), and fruit juice showed none after correction for multiple testing.
The US-based research team was primarily affiliated with the National Cancer Institute (NCI), part of the National Institutes of Health (NIH) in Bethesda, Maryland. Collaborators represented the University of South Carolina, Frederick National Laboratory for Cancer Research in Maryland, and the National Institute of Environmental Health Sciences in North Carolina.
Background
The oral microbiome comprises a complex microbial community whose members support metabolic and immune functions in the oral cavity.
In health, these microbial communities help maintain oral homeostasis. Changes in oral microbial composition have been linked to dental caries and periodontitis (inflammatory gum disease) and to systemic conditions, including cardiovascular disease (CVD), diabetes, and certain gastrointestinal cancers.
Because beverages are frequent dietary exposures that come into direct contact with the oral cavity, researchers have proposed that beverage intake may influence its microbial composition. Earlier investigations have often assessed broad dietary patterns or selected beverages rather than examining several beverage categories together.
Prior studies have yielded conflicting results regarding potential microbiome-associated effects of common beverages. Evidence remains limited for artificially sweetened beverages and fruit juice, while comparisons among individual alcoholic beverage types have produced mixed findings.
About the preprint
The present study aimed to address these knowledge gaps by investigating associations between beverage intake and oral bacterial diversity and composition. The sample cohort comprised a pooled dataset from 5,598 adults enrolled in nested case-cohort investigations within the United States (US) Agricultural Health Study (AHS), the NIH-AARP Diet and Health Study, and the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. Participants were selected for cancer risk studies, and the analyses accounted for the sampling design.
The study quantified participants’ dietary intake using the validated 124-item Diet History Questionnaire (DHQ), which assessed usual consumption over the preceding 12 months. Beverage intake was adjusted for total energy intake and expressed in grams per 1,000 calories. The researchers examined coffee, tea, alcoholic beverages (beer, wine, and liquor), SSBs, ASBs, and 100% fruit juice.
The researchers analyzed bacterial DNA from participants’ oral wash samples to characterize their oral microbial communities.
Taxonomy was assigned using the SILVA database. The researchers assessed alpha diversity, which describes bacterial diversity within individual samples, and beta diversity, which compares microbial communities between samples.
Preprint findings
Alcoholic beverages accounted for 25 of the 28 statistically significant genus-level associations across the six overall beverage categories. The researchers also identified associations for individual alcohol types, particularly beer and liquor.
Alcohol intake was positively associated with all three measures of alpha diversity. Individuals in the highest consumption tertile (T3) had approximately 10 more observed amplicon sequence variants (ASVs), a measure of bacterial richness, than non-consumers. Greater diversity alone does not establish whether an oral microbial community is healthier or less healthy.
Liquor showed the largest estimated association with bacterial richness, at approximately 15 additional ASVs compared with non-consumers. Wine and beer were each associated with approximately seven additional ASVs. Among individual alcohol types, only liquor showed associations across all three diversity measures, and the study did not establish that the richness estimates differed significantly between alcohol types.
In one analysis of differences between bacterial communities, alcohol was found to explain less than 1% of variation, the largest share among the beverages examined. Smoking status, age, and education each explained more variation than alcohol, while all beverages together accounted for approximately 4% of variation on this measure.
Higher alcohol intake was associated with greater model-estimated occurrence of Megasphaera and Peptostreptococcus, bacterial genera previously linked to poor oral health. The study did not measure whether participants had periodontal disease.
The highest alcohol-consumption tertile was associated with 23% lower expected abundance of Lautropia, a commensal genus often found at lower levels in dental disease, and lower relative abundance of Streptococcus.
Coffee had only three statistically significant genus-level associations, including higher relative abundance of Atopobium, whereas tea, SSBs, ASBs, and fruit juice had none after correction for multiple statistical comparisons. The absence of significant associations does not rule out smaller or more specific microbial effects.
Conclusions
The findings suggest that habitual alcohol consumption is associated with differences in oral microbial communities, including greater occurrence of some disease-associated genera and lower abundance of certain commensal bacteria. The authors suggest that these patterns could affect oral and systemic health, but the study did not test whether the microbial differences caused disease or contributed to cancer risk.
The authors emphasize that the study was cross-sectional, precluding causal inference, and that it relied on 16S rRNA sequencing, which limits species-level resolution. Dietary intake was self-reported, and the timing of dietary assessment and oral sampling differed across cohorts. The researchers also did not report oral hygiene practices or medication use, leaving room for residual confounding. Participants were predominantly non-Hispanic White, which may limit the generalizability of the findings. Longitudinal and mechanistic studies are needed to clarify whether these microbial associations have consequences for health.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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