Introduction:
The research study investigated whether drinking coffee or tea is associated with changes in the oral microbiome. The oral microbiome contains hundreds of bacterial species, and while many are harmless or beneficial, an unhealthy shift in their balance, called dysbiosis, can contribute to problems such as cavities or gum disease. Coffee and tea were of interest because they contain bioactive compounds, such as caffeine and polyphenols, that may influence bacterial growth and inflammation. The researchers wanted to determine whether people who drank different amounts of coffee or tea also had different types or amounts of oral bacteria.
Methods:
The researchers studied 938 adults from two large U.S. health studies. Participants reported how much coffee and tea they usually drank using food-frequency questionnaires. They also provided oral samples by using mouthwash, which collected bacteria from different areas of the mouth. Researchers then used 16S rRNA gene sequencing, a method that identifies bacteria by analyzing a specific part of their genetic material. Across all participants, the study generated about 9.9 million bacterial DNA sequences and identified 681 bacterial groups, called operational taxonomic units (OTUs). An OTU is a group of bacteria with very similar DNA and is often used as an estimate of a bacterial type or species. The researchers compared bacterial richness, diversity, and overall community composition between people with different levels of tea and coffee intake. Richness refers to how many different bacterial types are present, while diversity also considers how evenly those bacteria are distributed. The analysis also adjusted for factors such as age, sex, body mass index, smoking, alcohol use, and calorie intake that could otherwise affect the oral microbiome.
Results:
The strongest finding was that tea consumption was associated with noticeable changes in the oral microbiome, while coffee showed much weaker effects. For every additional cup of tea consumed per day, participants had an average of about 1.47 additional bacterial groups. Tea consumption was also significantly associated with greater Shannon diversity, with a P-value of 0.006, and greater community evenness, with a P-value of 0.009. The overall composition of the oral bacterial community also differed with tea intake, with a P-value of 0.002, and the differences were especially noticeable in people drinking three or more cups of tea per day compared with people who drank none. Tea was associated with increases in bacterial groups such as Fusobacteriales, Clostridiales, and Shuttleworthia satelles, while other bacteria, including Lactobacillales, Bifidobacteriaceae, and Kingella oralis, decreased. These findings show that tea was associated with a shift in the bacterial ecosystem rather than simply causing more bacteria to grow. Coffee, in contrast, was not significantly associated with overall bacterial richness, diversity, or community composition and affected only a small number of bacterial groups.
Limitations:
One major limitation is that this was a cross-sectional observational study. Because of this, the study can identify an association but cannot prove direct causation. In other words, it shows that people who drank more tea tended to have different oral bacteria, but it cannot prove that tea directly caused those differences. Tea drinkers may also have different diets, oral hygiene habits, or lifestyles that influence the oral microbiome. The researchers adjusted for several of these factors statistically, but it is impossible to remove every possible influence. Another limitation is that relatively fewer participants drank large amounts of tea, so there was less data available for frequent tea drinkers.
Conclusion:
Overall, the researchers concluded that tea consumption was associated with greater bacterial diversity and changes in the overall composition of the oral microbiome, while coffee had relatively little effect. However, greater bacterial diversity should not automatically be interpreted as healthier because some bacterial groups that increased with tea can also be associated with oral disease, while others that decreased may have different health effects. Therefore, the study mainly demonstrates that tea drinking is connected to a different oral bacterial environment, not that tea necessarily improves or harms oral health. Future controlled studies would be needed to determine whether tea directly causes these changes and whether the changes are beneficial or harmful.
