What happens on the surface of your tongue is about more than just the taste of food. In 60 healthy adults recruited from the United Kingdom and Belgium, the bacterial composition of this highly populated area was associated with the speed with which their brains processed information, suggesting a new link between mouth and cognition.
These results come from an exploratory study conducted by Joanna E. L’Heureux at the University of Exeter, in collaboration with UZ Brussels. Sixty adults, half in their 20s and the other half between 60 and 70, took a battery of ten tests of memory, attention and processing speed, while researchers took tongue swabs, saliva, blood and measured blood pressure.
Language, nitrates and cognitive performance
The authors start from a simple hypothesis: certain bacteria from tongue microbiota transform dietary nitrates into nitrites, then into nitric oxide (NO), a molecule that dilates blood vessels. After consuming beetroot, spinach or arugula, the nitrate passes into the blood, returns to the saliva, then the flora of the tongue activates it. Researchers point out that oral bacteria “therefore play a key role in the nitrate-nitrite-nitric oxide pathway“, write Joanna E. L’Heureux and her colleagues.
By linking these bacterial profiles to cognitive scores, the team highlighted a constant: people who harbored more Prevotella histicola responded more quickly to several mental tasks, in the United Kingdom and in Belgium.
Haemophilus parainfluenzae also appeared often in statistical models, but its association changed depending on the country and type of test, with for example better visual memory performance in Belgium and slower emotional responses in the United Kingdom.
Prevotella, Haemophilus and the effect of age
Prevotella histicola is, however, far from being a “magic” bacteria. In other works, it is associated with cavities or inflammation of the mouth, but here its greater abundance coincided with shorter reaction times. The authors raise the idea that certain oral species can support cerebral blood flow during mental effort via the production of NO, without being able to yet prove this mechanism.
Age weighed far more than any bacteria. In both countries, each additional year was accompanied by a slight decline in overall cognitive score and a slowdown in processing speed. On the microbial level, the researchers identified 17 species whose abundance differed between young and old. The latter presented more Treponema
and of Tannerellagenera related to gum disease, while Neisseria flavescensa nitrate-reducing species, was more common in younger people.
In this analysis, the place of residence of individuals was also important. “Geographic location emerged as the only significant predictor of microbial variation“, write the researchers.
A link to be handled with caution
Although this work has revealed interesting correlations, no link has been formally established. “The observed associations should therefore be considered exploratory, and larger studies will be needed to determine whether these trends reflect true biological differences or statistical variability.” conclude the authors.