Could Your Oral Bacteria Influence Memory Decline?
New Research Links the Oral Microbiome to Cognitive Health and Dementia Risk
The Hidden Connection Between Mouth and Mind
As people age, many experience mild cognitive impairment (MCI)—a condition marked by forgetfulness and difficulty focusing, which can progress to Alzheimer’s disease. Scientists have long known that genetics, especially carrying the APOE4 gene variant, plays a major role in dementia risk. But a new study suggests another surprising factor: the bacteria living in our mouths.
What the Study Explored
Researchers from the University of Exeter and collaborators in the UK investigated how the oral microbiome—the community of bacteria in the mouth—relates to memory, attention, and brain health. They studied 115 older adults, including 55 with MCI and 60 healthy controls, while also examining nitric oxide (NO) biomarkers, which are crucial for blood flow and brain function.
Their goal was to see whether certain bacteria might protect cognitive function, while others could increase dementia risk, especially in people with the APOE4 genotype.
Key Findings: Good vs. Bad Bacteria
Helpful bacteria: Higher levels of Neisseria and Haemophilus were linked to better memory, attention, and executive function in people with MCI. These bacteria also supported nitric oxide production, which keeps blood vessels healthy and may protect the brain.
Harmful bacteria: Prevotella intermedia, a microbe associated with gum disease, was more common in individuals carrying the APOE4 gene, suggesting it may contribute to higher dementia risk. Another bacteria, Porphyromonas, was strongly associated with MCI.
Balance matters: The study found that when “good” bacteria dominate, nitric oxide pathways that protect the brain are preserved. But when “bad” bacteria take over, nitric oxide availability is reduced, potentially accelerating cognitive decline.
Why It Matters
These results point to the oral microbiome as an early warning system for dementia risk. Importantly, the findings suggest that improving oral health—or even developing dietary or probiotic interventions—could help delay cognitive decline in vulnerable populations.
“Targeting oral bacteria that support nitric oxide production may offer a new way to protect the brain,” the researchers concluded.
The Takeaway
While brushing and flossing alone won’t prevent dementia, keeping your mouth healthy may be more important for your brain than we realized. The study opens the door to innovative treatments that could one day combine oral care, diet, and microbiome therapies to support memory and cognitive health.
Reference
L’Heureux, J.E., Corbett, A., Ballard, C., Vauzour, D., Creese, B., Winyard, P.G., Jones, A.M., & Vanhatalo, A. (2025). Oral microbiome and nitric oxide biomarkers in older people with mild cognitive impairment and APOE4 genotype. PNAS Nexus, 4(1), pgae543.