Whether you’re a quick or slow thinker depends on several factors, such as the efficiency of the brain’s wiring and the amount of gray matter in specific control centers. But there may be another, rather surprising influence, and that’s the bacteria in your mouth. Scientists have found an association between the mix of microbes on your tongue and how well the brain performs cognitive tasks as we age.
Previous studies have shown that poor oral health and gum disease are linked to cognitive impairment. Other research has found that nitrate from the food we eat can influence blood flow to the brain and cognitive performance.
So researchers led by Joanna E. L’Heureux at the University of Exeter in the United Kingdom wondered whether mouth bacteria involved in this pathway are linked to cognitive function.
It’s not as strange as it may sound. When we eat nitrate-rich foods like beets or leafy greens, nitrate enters our bloodstream and travels into our saliva. Friendly bacteria in our mouth then convert it into nitrite, which the body can turn into nitric oxide. This gaseous compound helps relax blood vessels and can increase blood flow to the brain.
What can our mouths reveal?
To investigate further, the research team recruited 15 younger adults and 15 older adults in Exeter and the same number in Brussels, Belgium. The reason for the two locations was to see if the links between mouth bacteria, aging and thinking skills were the same in different countries or unique to one place.
Each volunteer completed a set of 10 tests that assessed memory, processing speed and focus. The researchers collected tongue swabs and blood and saliva samples and measured blood pressure.
They then sequenced the DNA in the swabs to identify which bacteria were present. Finally, the scientists compared each person’s oral microbial community with their test performance.
A complicated picture emerges
People in both countries with higher levels of Prevotella histicola in their mouth showed faster reaction times on different cognitive tasks. But the results for another microbe, Haemophilus parainfluenzae, were mixed.
In the U.K., higher levels were linked to faster responses on tests involving reasoning and spatial awareness but slower responses when recognizing emotions. In Belgium, higher levels were associated with faster responses on visual memory tests and better performance on a working memory test.
The researchers also identified 17 bacterial species that differed in abundance between younger and older adults. One nitrate-converting species, Neisseria flavescens, was more abundant in younger participants in both countries, though it was not directly linked to cognitive test scores. Older adults had higher levels of bacteria tied to gum disease, such as Treponema and Tannerella.
Where people lived was also important. “In the RDA [redundancy analysis], geographical location emerged as the only significant predictor of microbial variation,” the researchers write.
Although their study published in the journal PLOS One focused on mouth bacteria, age was consistently and strongly associated with cognitive performance. Older participants scored lower on processing speed and some memory tests in both countries.
While the research revealed some interesting connections, no firm link has been established. “The observed associations should therefore be considered to be exploratory, and larger studies will be required to determine whether these patterns reflect true biological differences or statistical variability.”
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Publication details
Joanna E. L’Heureux et al., Oral microbiome signatures of ageing and cognitive function across distinct geographical cohorts, PLOS One (2026). DOI: 10.1371/journal.pone.0359559
Journal information:
PLoS ONE
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The bacteria on your tongue could be linked to your brainpower (2026, October 12)
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