Authors:
Najwane Said-Sadier, Batoul Sayegh, Raymond Farah, Linda Abou Abbas, Rania Dweik,
Norina Tang, David M Ojcius
Journal Reference:
Said-Sadier, N., Sayegh, B., Farah, R., Abbas, L.A., Dweik, R., Tang, N. and Ojcius, D.M., 2023. Association between periodontal disease and cognitive impairment in adults.
International Journal of Environmental Research and Public Health, 20(6), p.4707. https://doi.org/10.3390/ijerph20064707
Background:
Periodontal disease (PD) is a chronic systemic inflammatory condition primarily caused by gram-negative bacteria such as Porphyromonas Gingivalis. PD leads to the destruction of periodontal tissues, resulting in attachment loss and alveolar bone destruction. PD has traditionally been considered a localised oral condition. However, emerging evidence suggests it may also contribute to systemic inflammation, with potential health implications beyond the oral cavity.
Alzheimer’s disease (AD) is one of the most common neurodegenerative diseases and is characterised by progressive neuronal destruction, leading to cognitive decline and neuroinflammation. New research suggests this can occur through direct bacterial invasion via the bloodstream and crossing of the blood–brain barrier, or indirectly through activation of systemic immune responses. The “inflammation hypothesis” explains that chronic inflammatory conditions, such as PD, may trigger or accelerate the neurodegenerative process. Periodontal pathogens and their components, including lipopolysaccharides (LPS), have been detected in the brains of AD patients and shown to stimulate glial cells to release neurotoxic inflammatory mediators. With an ageing global population and rising prevalence of dementia, understanding modifiable risk factors such as oral health is crucial.
Aims:
To evaluate current evidence linking periodontitis with cognitive impairment and
dementia in adults.
Methods:
This review followed PRISMA 2020 guidelines and the PICO framework to form the
research question. A literature search of PubMed, Web of Science and CINAHL was
conducted for studies published up until September 2021. This review included
observational studies assessing quantitative measures for the association between
periodontal disease and dementia or neuroinflammation among adults. Study quality
was assessed using the Newcastle Ottawa Scale (NOS). 11 high-quality studies met the
inclusion criteria (6 cohort, 3 cross-sectional and 2 case-control studies).
PD was assessed using clinical measures, ICD Codes, presence of oral pathogens, and
presence of induced serological inflammatory biomarkers and antibodies. Validated
assessment tools such as the MMSE (Mini-Mental State Examination) and MOCA
(Montreal Cognitive Assessment test) to assess cognitive outcomes.
Results:
The studies included in this review demonstrated an association between periodontal disease and cognitive impairment or dementia. Long-term exposure to chronic periodontitis was linked to an increased risk of Alzheimer’s disease and overall dementia, even after adjusting for confounding factors such as age, sex, lifestyle behaviours, and comorbidities.
Multiple studies reported that individuals with both periodontal disease and cognitive impairment showed altered inflammatory and immune biomarker profiles. Gingival inflammation was consistently identified as a key predictor of cognitive decline. Elevated antibodies against periodontal pathogens, especially P. gingivalis, were linked with poorer memory performance.
Dysregulation of inflammatory mediators such as IL-1β, IL-6, TNF-α, and MCP-1 supports the role of systemic inflammation in neurodegeneration. Proposed mechanisms include direct microbial invasion across the blood–brain barrier, immune mediated neuroinflammation, impaired amyloid-β clearance, and disruption of signalling pathways essential for neuronal survival and memory function.
Conclusion:
This systematic review provides strong evidence supporting an association between PD and cognitive impairment. Although causality cannot be definitively established, chronic periodontal inflammation may contribute to neurodegeneration through systemic inflammatory and immune-mediated pathways. These findings highlight the importance of maintaining good oral health for broader cognitive and systemic health.
Research Summary Written By: Livia Yang, University of Liverpool – BDS 4