New research suggests that bacteria in your mouth and on your tongue may be connected to changes in brain function as you age.
A 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. One possibility is that harmful bacteria enter the bloodstream directly, potentially damaging the brain. Alternatively, an imbalance between beneficial and harmful bacteria may reduce the conversion of nitrate—abundant in vegetable-rich diets—into nitric oxide, a chemical essential for brain communication and memory formation.
Key Findings: Beneficial and Harmful Bacteria
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.”
Mild Cognitive Impairment and Dementia Risk
While a decline in memory and brain functions is typical in old age, deteriorations in mental capabilities that are greater than would be expected with normal aging 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 analyzed and the bacteria population was 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: “Oral microbiome and nitric oxide biomarkers in older people with mild cognitive impairment and APOE4 genotype” by Joanna E L’Heureux, Anne Corbett, Clive Ballard, David Vauzour, Byron Creese, Paul G Winyard, Andrew M Jones and Anni Vanhatalo, 28 January 2025, PNAS Nexus.
DOI: 10.1093/pnasnexus/pgae543
