Scientists from New York University found older adults with more “bad” than “good” bacteria in their gums are more likely to have evidence for amyloid beta—a key biomarker for Alzheimer’s disease—in their cerebrospinal fluid.
However, this imbalance in oral bacteria was not associated with another Alzheimer’s biomarker called tau.
The study adds to the growing evidence of a connection between periodontal disease (gum disease) and Alzheimer’s.
The research is published in Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring and was conducted by Angela Kamer et al.
Periodontal disease—which affects 70% of adults 65 and older –is characterized by chronic and systemic inflammation, with pockets between the teeth and gums enlarging and harboring bacteria.
Alzheimer’s disease is characterized by two hallmark proteins in the brain: amyloid beta, which clumps together to form plaques and is believed to be the first protein deposited in the brain as Alzheimer’s develops, and tau, which builds up in nerve cells and forms tangles.
In the study, the team examined 48 healthy, cognitively normal adults ages 65 and older.
Participants underwent oral examinations to collect bacterial samples from under the gumline, and lumbar puncture was used to obtain CSF in order to determine the levels of amyloid beta and tau.
To estimate the brain’s expression of Alzheimer’s proteins, the researchers looked for lower levels of amyloid beta (which translate to higher brain amyloid levels) and higher levels of tau (which reflect higher brain tangle accumulations) in the CSF.
The team quantified bacteria known to be harmful to oral health (e.g., Prevotella, Porphyromonas, Fretibacterium) and pro-oral health bacteria (e.g. Corynebacterium, Actinomyces, Capnocytophaga).
They found that individuals with an imbalance in bacteria, with a ratio favoring harmful to healthy bacteria, were more likely to have the Alzheimer’s signature of reduced CSF amyloid levels.
They hypothesize that because high levels of healthy bacteria help maintain bacterial balance and decrease inflammation, they may be protective against Alzheimer’s.
The results show the importance of the overall oral microbiome—not only of the role of ‘bad’ bacteria but also ‘good’ bacteria—in modulating amyloid levels.
The researchers did not find an association between gum bacteria and tau levels in this study, so it remains unknown whether tau lesions will develop later or if the people will develop the symptoms of Alzheimer’s.
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If you care about Alzheimer’s disease, please read studies about the cause of memory loss in Alzheimer’s disease, and what is the difference between dementia and Alzheimer’s disease.
For more information about brain health, please see recent studies about a new method to treat Alzheimer’s disease, and results showing brain damage could be stronger in COVID-19 than in Alzheimer’s disease.
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