Association Between Oral Bacteria and Alzheimer's Disease: A Systematic Review and Meta-Analysis.
Level 3 - non-randomized controlled study
Systematic review of observational (case-control and cross-sectional) studies
PubMed 36404545 · doi:10.3233/JAD-220627
What was done
Authors conducted a systematic review and random-effects meta-analysis across six databases (PubMed, Embase, Cochrane Central Library, Scopus, ScienceDirect, and Web of Science) evaluating clinical studies on oral bacteria and Alzheimer's disease (AD). Methodological quality was appraised, and evidence was synthesized qualitatively and quantitatively across 16 included studies (10 examining periodontal pathobionts and 6 microbiome-wide association studies) evaluating brain, serum, and oral samples.
What was found
The presence of oral bacteria in brain tissue was associated with a significant increase in AD risk (OR = 10.68, 95% CI: 4.48–25.43; p < 0.00001, I² = 0%). Detection of *Porphyromonas gingivalis* in the brain specifically was also associated with increased risk (OR = 6.84, 95% CI: 2.70–17.31; p < 0.0001, I² = 0%). Patients with AD showed lower oral microbiota alpha diversity than healthy controls, though specific bacterial community patterns were inconsistent across studies.
Why it matters
This review quantifies the clinical link between oral dysbiosis, brain colonization by oral pathobionts like *P. gingivalis*, and AD, supporting hypotheses that periodontal pathogens may contribute to neurodegenerative pathology.
Limits
The underlying studies are observational (primarily post-mortem or cross-sectional), which cannot establish causality or determine whether bacterial invasion is a cause or consequence of blood-brain barrier breakdown in AD. Total sample size was not reported in the abstract, and community-level microbiome findings were heterogeneous across studies.
Cited by
- supports Porphyromonas gingivalis in the oral cavity is directly linked to an increased risk of Alzheimer's disease.