The Link Between the Oral Microbiome and Dementia

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A new study suggests that the microbial ecosystems in our mouths may influence cognitive function as we age, with potential dietary interventions to delay cognitive decline.

According to the study, published in PNAS Nexus, about 15 percent of older adults experience mild cognitive impairment (MCI), a key risk factor for dementia and Alzheimer’s disease. Previous research has linked gum disease to worsened cognitive function, and this study identifies possible mechanisms: oral bacteria may enter the bloodstream and travel to the brain or displace nitrate-reducing bacteria needed to produce nitric oxide, which supports brain functions like memory.

The study analyzed the oral microbiomes of 115 participants, including 55 with MCI. Results showed that a higher abundance of Neisseria bacteria was associated with better cognitive function, including executive function and attention in the MCI group and working memory in healthy individuals. In contrast, Porphyromonas was linked to MCI, while Prevotella intermedia was associated with carrying the APOE4 allele, a genetic risk factor for Alzheimer’s.

“These results give rise to a novel hypothesis that the balance between two metabolic pathways for nitrate reduction within the oral ecosystem, denitrification and DNRA, is skewed toward DNRA in MCI and potentially modulated by APOE4 status,” the study read.

Researchers noted that diet can influence the oral microbiome, and nitrate-rich diets, such as the Mediterranean and DASH diets, promote bacteria associated with better cognitive outcomes. According to the authors, these findings suggest potential strategies to support brain health through diet and oral microbiome management.