Oral Bacteria May Influence How Quickly We Think

Among 60 healthy adults from the United Kingdom and Belgium, researchers found that the abundance of certain bacteria on the tongue was associated with performance on cognitive tests.

This may seem surprising, but consider what happens when you eat a mouthful of beetroot. Some of its nitrates enter the bloodstream and then, taking an unexpected detour, return to the mouth.

Bacteria on the tongue help convert these nitrates into a substance the body can use to produce nitric oxide, a molecule that helps blood vessels widen.

This small chemical journey is one reason scientists are investigating whether microbes in the mouth are associated with memory, attention, and information-processing speed.

To better understand this relationship, researchers led by Joanna E. L'Héreault of the University of Exeter, in collaboration with colleagues from Vrije Universiteit Brussel, recruited 15 younger and 15 older adults in each country.

The younger participants were generally around 20 years old, while the older participants were, on average, between 60 and 70.

Participants completed tests assessing memory, attention, emotion recognition, and information-processing speed. The team also measured blood pressure and collected blood and saliva samples, along with tongue swabs.

All participants were non-smokers. People who had recently taken antibiotics or had a history of oral disease were excluded from the study.

After identifying the bacteria in the swabs, the researchers compared each participant's oral microbiome with their cognitive test results.

One finding was consistent across both countries. People with higher levels of Prevotella histicola responded more quickly on certain tests, although the tasks differed between the two countries.

Another species, Haemophilus parainfluenzae, showed a more mixed pattern. In Belgium, it was associated with faster responses on emotion-recognition and visual-learning tasks, as well as greater working-memory accuracy. In the UK, it was associated with faster responses on some tasks but slower responses on emotion recognition.

Thus, higher levels of a particular bacterium did not necessarily correspond to better performance across all tests.

Age itself was the most consistent predictor of cognitive performance: in both countries, older age was associated with lower overall scores and slower responses.

The researchers also found that the abundance of 17 bacterial species differed between younger and older participants.

At a broader taxonomic level, bacteria from the genera Treponema and Tannerella, which include species associated with gum disease, were more abundant in older adults. One nitrate-reducing bacterial species was more abundant among younger participants.

However, finding this bacterium more frequently in younger people's mouths did not automatically mean it was a marker of better cognitive performance. The same nitrate-reducing species was also more prevalent in the UK group, which had lower overall test scores.

All participants were healthy and underwent cognitive testing. These differences reflected variation among healthy individuals rather than diagnoses of cognitive impairment.

Geography also played an important role. The bacterial communities differed between participants in the UK and Belgium, although some age-related patterns were observed in both countries.

The study builds on earlier research by the same group, published in PNAS Nexus in 2025, which examined oral microorganisms and nitric oxide biomarkers in older adults, including people with mild cognitive impairment.

The new study investigated whether similar associations could be observed among healthy younger and older adults in two countries.

The results of the chemical measurements were mixed. In the UK, higher plasma nitrate levels were associated with better performance on one test but lower accuracy in emotion recognition. Higher nitrite levels were associated only with slower responses.

The chemical process involving oral bacteria is also relevant to research on the effects of beetroot on physical performance. Bacteria convert nitrate into nitrite, which can subsequently contribute to nitric oxide production.

However, the new study did not establish that this process caused the differences in test performance. Nor did it investigate whether changing the composition of the oral microbiome could improve cognitive abilities.

With only 30 participants in each country, the findings are preliminary. The authors note that larger studies are needed to distinguish genuine biological patterns from statistical variation.

Diet was not controlled, and physical activity and sleep were not assessed comprehensively. These factors could have influenced both the oral microbiome and cognitive test results.

Data were collected between 2017 and 2019. Belgian samples were transported to the UK in liquid nitrogen, and the authors acknowledge that differences in storage conditions could have introduced measurement errors.

The paper describes adjustments for multiple comparisons in some analyses, but not in the regressions linking bacteria to cognitive test results. Testing numerous associations can increase the likelihood that apparently significant findings arise by chance.

The research team compared younger and older adults rather than following individuals as they aged. Consequently, the study cannot establish whether oral bacteria predict cognitive decline or influence its rate.

The findings therefore do not prove that changing the oral microbiome can prevent dementia, improve memory, or slow brain aging.

For now, certain oral bacteria appear to be associated with differences in cognitive performance. Further research is needed to determine whether these microbes contribute to those differences or instead reflect other factors shared by oral health and brain function.