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Your oral microbiome might predict cognitive decline before symptoms start, study suggests
In a nutshell
- Research involving 120 older adults found that certain mouth bacteria were linked to better cognitive test scores, while others were associated with mild cognitive impairment, suggesting oral health may play a role in brain health.
- People carrying the APOE4 gene (which increases Alzheimer’s risk) had higher levels of a specific type of bacteria called Prevotella intermedia in their mouths, indicating genetic factors might influence oral bacterial communities.
- The study found that people with higher levels of beneficial bacteria like Neisseria and Haemophilus performed better on memory and thinking tests, though more research is needed to understand if this relationship is causal.
EXETER, England — Most people know that brushing and flossing help prevent cavities and gum disease, but maintaining good oral health might also be linked to brain function as we age. A new study reveals intriguing associations between the bacteria living in our mouths and cognitive health.
Scientists at the University of Exeter and their collaborators studied the mouth bacteria of 120 older adults. Half of these participants had mild cognitive impairment (MCI), a condition that can affect memory and thinking skills and may increase the risk of developing dementia. The other half were healthy adults of similar ages.
Their research, published in PNAS Nexus, uncovered patterns in the bacterial communities living in participants’ mouths. Two types of bacteria, Neisseria and Haemophilus, were associated with better performance on memory and thinking tests. Meanwhile, different bacteria, particularly Prevotella, were linked to lower scores on these tests.
One of the study’s most notable findings involved a gene called APOE4, which increases a person’s risk of developing Alzheimer’s disease. People carrying this gene tended to have higher levels of a specific type of bacteria called Prevotella intermedia in their mouths. This suggests that genetic factors may be associated with variations in oral bacterial composition, though the study did not establish a direct causal link.
The researchers also examined how these bacteria might be linked to biochemical processes in the body. Some oral bacteria help process nitrate, a compound found in foods like beetroot and leafy greens, converting it into molecules that play a role in circulation and brain function. The study found that people with more Neisseria and Haemophilus bacteria had microbial communities associated with nitrate-related biochemical pathways, though it did not prove that these bacteria directly improve nitrate processing.
Another significant finding involved a type of bacteria called Porphyromonas gingivalis, which is known to cause gum disease. Participants with mild cognitive impairment had higher levels of these bacteria compared to those without cognitive problems. This adds to growing evidence linking oral health and brain health.
The research team also discovered that certain combinations of bacteria seemed particularly important. The Neisseria-Haemophilus combination showed the strongest statistical association with cognitive test performance, especially in participants with mild cognitive impairment. However, it’s important to note that the study only identified associations; it did not prove that these bacteria directly influence cognitive function.
These findings may be particularly relevant for people who carry the APOE4 gene. Since these individuals tend to have different bacterial patterns in their mouths, paying extra attention to oral health might be beneficial. However, more research is needed to determine whether specific dental care strategies could help reduce cognitive decline risk.
With global dementia rates expected to surge, this research highlights a potential factor in cognitive health. The microscopic communities in our mouths might hold one key to maintaining cognitive function as we age—making regular dental care more important than ever.
Paper Summary
Methodology
The researchers collected mouth rinse samples from participants using a standardized protocol. Each participant swished a specific mouthwash for 30 seconds before providing their sample. The research team then extracted bacterial DNA from these samples and used advanced genetic sequencing to identify and quantify different bacterial species. Participants also completed various cognitive tests measuring memory, attention, and executive function. The scientists employed statistical analyses to explore associations between bacterial communities, cognitive performance, and genetic risk factors.
Results
The study found distinct bacterial patterns between participants with mild cognitive impairment and healthy controls. The Neisseria-Haemophilus bacterial group was associated with better cognitive performance, particularly in tests of memory and executive function. Two key findings emerged: Porphyromonas bacteria were associated with mild cognitive impairment, while Prevotella intermedia was linked to APOE4 carrier status.
Limitations
Most participants were female, which might limit the study’s applicability to males. The research could not determine whether changes in oral bacteria cause cognitive decline or result from it. Additionally, the genetic sequencing technique used has some limitations in identifying bacteria at the species level. Diet and lifestyle factors, which could influence both oral bacteria and cognitive function, were not fully accounted for in the analysis.
Discussion and Takeaways
This research suggests that oral health may be linked to cognitive aging. The balance between different types of oral bacteria appears important, with some associated with beneficial biochemical pathways and others potentially linked to cognitive decline. These findings could lead to new preventive strategies, including targeted probiotics or dietary interventions designed to encourage beneficial bacteria while limiting harmful ones. However, further studies are needed to confirm these associations and explore potential interventions.
Funding and Disclosures
The research received funding from several organizations, including the National Institute for Health and Care Research, the University of Exeter, and other institutions. Some researchers disclosed consulting relationships with pharmaceutical companies, though these relationships did not influence the study’s conduct or results.
Publication Information
The study appeared in PNAS Nexus, 2025, Volume 4, page 543, titled “Oral microbiome and nitric oxide biomarkers in older people with mild cognitive impairment and APOE4 genotype” by Joanna E. L’Heureux and colleagues from the University of Exeter Medical School and partner institutions.
