Mouth bacteria may hold insight into your future brain function, finds study

The bacteria in your mouth and on your tongue may be linked to changes in brain function as you age, new research suggested.

The study, led by the University of Exeter, found that certain bacteria were associated with better memory and attention, while others were linked to an increased risk of Alzheimer’s disease.

The researchers identified two possible ways these bacteria may impact brain health. This includes harmful bacteria directly entering the bloodstream, potentially causing damage to the brain. Alternatively, an imbalance between beneficial and harmful bacteria can reduce the conversion of nitrate (abundant in vegetable-rich diets) to nitric oxide -a chemical crucial for brain communication and memory formation.

Individuals who had large numbers of the bacteria groups Neisseria and Haemophilus had better memory, attention and ability to do complex tasks. These people also had higher levels of nitrite in their mouths.

On the other hand, greater levels of the bacteria, Porphyromonas, was more common in individuals with memory problems. Whereas the bacterial group Prevotella, was linked to low nitrite, which the researchers predict could in turn could mean poorer brain health and was more common in people who carry the Alzheimer’s Disease risk gene, APOE4.

The study was supported by Wellcome and part funded by the National Institute for Health and Care Research (NIHR) Exeter Biomedical Research Centre. poses an interesting possibility for early identification and intervention.

Lead author Dr Joanna L’Heureux, of the University of Exeter Medical School, said: “Our findings suggest that some bacteria might be detrimental to brain health as people age.  It raises an interesting idea for performing routine tests as part of dental checkups to measure bacterial levels and detect very early signs of declining brain health.”

While decline in memory and brain functions is typical in old age, deteriorations in mental capabilities that is greater than would be expected with normal ageing is known as Mild Cognitive Impairment. Approximately 15% of older adults fall into the category of mild cognitive impairment, considered the greatest risk factor for the development of dementia or Alzheimer’s disease.

Published in PNAS Nexus, the study recruited 110 participants, over the age of 50 from an online study called PROTECT that tracks the brain health of more than 25,000 middle-aged people in the UK. Researchers split participants into two groups: those with no brain function decline and those showing Mild Cognitive Impairment. The participants in these two groups sent in mouth rinse samples that were then analysed and the bacteria population studied.

Co-author Professor Anne Corbett, of the University of Exeter Medical School, said: "The implication of our research is profound. If certain bacteria support brain function while others contribute to decline, then treatments that alter the balance of bacteria in the mouth could be part of a solution to prevent dementia. This could be through dietary changes, probiotics, oral hygiene routines, or even targeted treatments.”

Reference:

Joanna E L’Heureux, Anne Corbett, Clive Ballard, David Vauzour, Byron Creese, Paul G Winyard, Andrew M Jones, Anni Vanhatalo, Oral microbiome and nitric oxide biomarkers in older people with mild cognitive impairment and APOE4 genotype, PNAS Nexus, Volume 4, Issue 1, January 2025, pgae543, https://doi.org/10.1093/pnasnexus/pgae543