The curious connection between oral bacteria and our thinking speed

Researchers say the bacteria in our mouths can be linked to our thinking speed.

A new study has revealed some intriguing statistical links between the bacteria on our tongues and how quickly the brain processes information.

According to Ambassador Arjan, among 60 healthy adults in the UK and Belgium, the frequency of some tongue bacteria was related to performance in cognitive tests.

It may sound strange, but consider that when you swallow a piece of beetroot, some of its nitrates enter your bloodstream, then take an unexpected route and end up back in your mouth.

Bacteria on your tongue help turn it into a substance your body can use to make nitric oxide (a molecule that helps dilate blood vessels).

This little chemical trip is one of the reasons why scientists are investigating whether the microbes in our mouths are linked to our memory, attention and speed of information processing.

Researchers led by Joanna E. Joanna E. L'Heureux at the University of Exeter and her colleagues at the Vrije University of Brussels recruited 15 young adults and 15 adults in each country to better understand this connection.

The younger cohorts were generally in their twenties, while the older cohorts were on average in their sixties or seventies.

Participants completed tests of memory, attention, emotion recognition, and processing speed. The team also measured blood pressure and collected blood, saliva and tongue swabs.

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

By identifying the bacteria in those swabs, the researchers were able to compare each person's oral microbial community with their test performance.

A finding appeared in both countries. People with more of the bacterium Prevotella histicola responded faster in certain tests, although the tasks differed between countries.

Another species, Haemophilus parainfluenzae, showed a mixed pattern. In Belgium, this bacterium was associated with faster responses in emotion recognition and visual learning tasks and better working memory accuracy. In the UK it was associated with faster responses on some tasks but slower responses on emotion recognition.

So having more of a particular bacteria didn't necessarily mean better performance in all tests. Age alone was the most consistent predictor of cognitive performance; That is, older age was associated with lower overall scores and slower responses in both countries.

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

At a broader grouping level, bacteria of the Treponema and Tannerella strains, which include species associated with gum disease, were more abundant in older adults.

A nitrate-reducing species was more abundant in younger participants, but a bacterium being more common in young people's mouths did not automatically make it a marker of better cognition. The same nitrate-reducing species was also more abundant in the British group with lower overall test performance.

All participants were healthy and had undergone cognitive screening. These differences were indicative of variation among healthy individuals and not a diagnosis of cognitive impairment.

Geography was another important part of this picture. Bacterial communities differed between British and Belgian participants, even though some age-related patterns emerged in both locations.

The study builds on a previous study from the same group, published in PNAS Nexus in 2025, that examined oral microbes and nitric oxide biomarkers in older adults, including those with mild cognitive impairment.

This new study examined whether similar associations exist in younger and older healthy adults in the two countries.

Chemical measurements were different. In the UK, higher plasma nitrate was associated with better performance on a test, but poorer emotion recognition accuracy. Higher nitrite was only associated with slower responses.

The chemical pathway related to oral bacteria is also related to research on beets and physical performance. The bacteria convert nitrate to nitrite, which can subsequently help produce nitric oxide, but the new study did not show that this process made a difference in the tested performance. It also did not test whether changing a person's oral bacteria could improve their cognitive performance.

These findings are exploratory with only 30 participants per country. Larger studies are needed to discern true biological patterns from statistical variation, the authors say.

Diet was not controlled and physical activity and sleep were not comprehensively assessed. These things can affect both the bacteria in a person's mouth and his performance in cognitive tests.

Data were collected between 2017 and 2019. The Belgian specimens were transported to the UK in liquid nitrogen and the authors acknowledge differences in storage conditions which could account for the variability.

This article describes multiple comparison corrections for some analyses, but not for regressions relating bacteria to cognitive tests. Testing for multiple connections can increase the likelihood of apparent findings due to chance.

Instead of following people throughout their lives, the team compared younger and older people. It cannot determine whether oral bacteria predict or influence the rate of cognitive decline.

Therefore, the results do not suggest that altering oral microbes prevents dementia, improves memory, or slows brain aging.

Some oral bacteria now appear to be associated with differences in thinking skills. Whether these microbes help shape the differences or reflect other influences that the mouth and brain share remains to be seen.

This research has been published in the journal PLOS ONE.