New research adds to growing evidence of the connection between oral and overall health, suggesting that bacteria in the mouth—both beneficial and harmful—may influence cognitive function.
Researchers from the University of Exeter in the UK studied 110 participants over the age of 50, assessing their working memory, executive function, verbal reasoning and visual attention. They also analyzed the bacteria present in their mouths using rinse samples.
The study, published in PNAS Nexus, found that individuals with higher levels of Porphyromonas, a key pathogen in chronic periodontitis, were more likely to experience memory issues. Additionally, the bacteria Prevotella, commonly associated with periodontal disease, was linked to the presence of the APOE4 gene, a known risk factor for Alzheimer’s disease.
Mild cognitive impairment (MCI) is already considered a major risk factor for Alzheimer’s, with about 10 per cent of people with MCI progressing to dementia each year.
“We showed that the genus Porphyromonas was more abundant in MCI than in healthy controls, supporting the notion that the presence of elevated oral Porphyromonas precedes dementia diagnosis,” the researchers wrote.
The good bacteria
Meanwhile, participants with higher levels of Neisseria and Haemophilus—bacteria linked to better oral health—performed better in cognitive tasks related to memory and attention.
The researchers called for further studies into the link between the oral microbiome and brain health, highlighting the potential for interventions that promote beneficial bacteria to help delay cognitive decline.
Currently, oral health is not included among the 14 recognized risk factors for dementia. However, scientists at New York University’s Rory Meyers College of Nursing have urged the medical community to consider it, citing their own research and a growing body of evidence. They argue that preventive measures, such as improving oral health, could play a role in reducing dementia risk, particularly as the global population ages.
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