Scientists talked about the connection of the oral microbiome with cognitive abilities

German scientists have found that the composition of bacteria in the gingival pockets is directly related to cognitive abilities, brain volume and the level of inflammation in people without dementia. The study is published in The Lancet journal.

The authors from the University Medical Center Hamburg-Eppendorf analyzed data from 1,026 participants aged 46 to 78 years. Samples were taken from the four deepest gingival pockets of each individual and, using 16S rRNA sequencing, the composition of the microbial community was determined — a total of 85 bacterial genera were identified. Participants also underwent an MRI scan of the brain, cognitive testing, blood tests for inflammatory markers, and a dietary assessment.

Topological analysis of the data revealed a continuous "pathogenicity gradient": the bacteria characteristic of periodontitis, Porphyromonas, Fusobacterium, Treponema, and Dialister, were concentrated at one pole of the microbial map. On the other, there are species associated with a healthy oral cavity, in particular Streptococcus and Rothia. Participants with a predominance of pathogenic bacteria showed significantly lower cognitive test scores, an increased number of white blood cells in the blood, and less adherence to the MIND diet, a diet designed to prevent neurodegenerative diseases.

A separate result was the relationship between the composition of the microbiome and the morphology of the brain: carriers of the pathogenic profile showed a decrease in the thickness of the cortex and a decrease in the volume of subcortical structures. In addition to Porphyromonas and Fusobacterium, which were previously associated with Alzheimer's disease, scientists for the first time found an association with cognitive functions in the genera Fretibacterium, Tannerella and Parvimonas, which had not previously appeared in brain research.

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The suspected mechanism of action is systemic inflammation, disruption of the blood—brain barrier, and direct neurodegenerative effects of bacterial toxins.

The authors emphasize that the design of the study does not allow to establish a causal relationship: the reverse logic is also possible, in which cognitive decline worsens oral hygiene, which contributes to the growth of pathogenic flora. Longitudinal and interventional studies are needed to distinguish between these scenarios.

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