The mouth hosts a complex community of microorganisms that may influence more than hygiene. Scientists are increasingly investigating whether these bacteria are associated with memory, attention, and the speed of mental processing as people age.

A study published in PLOS ONE on October 5, 2026, examined the relationship between tongue bacteria and cognitive performance in younger and older adults from the United Kingdom and Belgium. The results revealed several intriguing associations, although they do not establish that bacteria directly improve or impair thinking abilities.

Investigating the Microbiome and Cognitive Performance

The microbiome refers to the community of microorganisms living throughout the mouth, including on the tongue. These microbes interact with their surroundings and participate in processes that support normal health. Changes in microbial composition have also been associated with gum disease and other health concerns.

Researchers led by Joanna E. L’Heureux at the University of Exeter investigated whether differences in tongue bacteria were associated with cognitive performance across age groups and geographical locations.

The study included 60 healthy adults: 30 participants in Exeter, England, and 30 in Brussels, Belgium. Each location contributed 15 younger and 15 older. Participants completed 10 cognitive assessments examining abilities such as memory, attention, reasoning, visual processing, and reaction speed.

Researchers collected tongue swabs, blood samples, and saliva to examine microbial composition and measure compounds involved in nitrate metabolism. Comparing these biological measurements with cognitive test results helped the team investigate whether particular microbial patterns were associated with specific mental abilities.

Which Bacteria Showed Notable Associations?

One notable finding involved Prevotella histicola. Participants with greater relative abundance of this bacterial species tended to respond more quickly across several cognitive tasks. However, reaction speed represents only one aspect of cognition and does not necessarily indicate better overall memory, reasoning, or accuracy.

Another species, Haemophilus parainfluenzae, showed more varied associations. Among participants in the United Kingdom, greater abundance was associated with faster responses on certain reasoning and spatial-awareness assessments but slower responses during an emotion-recognition task. In Belgium, associations included faster visual-memory responses and stronger working-memory performance.

The researchers also identified 17 bacterial species that differed in relative abundance between younger and older adults. Neisseria flavescens, which participates in nitrate conversion, was more abundant among younger participants in both countries. However, it was not directly associated with cognitive test scores in this study.

How Nitrate-Processing Bacteria May Matter

One possible connection between bacteria and cognitive health involves nitric oxide, a signaling molecule that helps regulate blood vessel function. When nitrate-rich foods such as beetroot and leafy greens are consumed, nitrate enters the bloodstream and can accumulate in saliva. Certain bacteria convert nitrate into nitrite, which can subsequently contribute to nitric oxide production. This process may help support circulation, including the delivery of blood to the brain.

Expert Insight

The study's authors, led by Joanna E. L’Heureux, emphasized the importance of considering geographical differences when investigating the microbiome. Their peer-reviewed article in PLOS ONE states: “These findings emphasise the need to account for geographic context in microbiome-health research.”

What the Findings Mean for Everyday Health

The research provides another reason to take health seriously, but it does not establish that changing tongue bacteria will improve memory or prevent cognitive decline. Regular brushing with fluoride toothpaste, cleaning between teeth, attending dental checkups, and seeking treatment for persistent gum problems remain sensible measures for maintaining health.

A study involving 60 adults in the United Kingdom and Belgium found associations between selected tongue bacteria, age, and performance on certain cognitive tasks. The findings raise interesting questions about how microbial communities and nitrate metabolism may relate to cognitive health.

However, the study was small and exploratory, and its results do not establish cause and effect. Some associations also differed between locations and cognitive assessments. Maintaining good hygiene remains worthwhile, but further research is needed before specific bacteria can be used to predict or improve cognitive performance.