Alzheimer’s disease is a leading cause of degenerative dementia with prevalence increasing with age. Periodontal disease has a high prevalence and incidence increases with age as well. With multiple common risk factors a systematic review and meta-analysis was published in 2017 in the journal Neuroepidemiology that aimed to provide existing evidence, to date, investigating the association between periodontal disease and Alzheimer’s disease.1
The authors start by suggesting a possible pathway linking both diseases. Leira et al suggests, the pathway linking both diseases may be “the invasion of the brain tissue by periodontal bacteria residing in the dental biofilm.” Leira et al goes on to state the invasion by the bacteria may occur via the bloodstream or peripheral nerves, which could accelerate neuroinflammation.
Upon the literature search a total of 550 articles were identified via the authors search strategy. However, after exclusion for multiple reasons 5 papers were included in the systematic review, of which 3 were used for the meta-analysis.
The overall results showed a strong association between periodontal disease and Alzheimer’s disease, in spite of the small number of studies included. In one study periodontal clinical parameters were higher in patients with Alzheimer’s disease when compared to healthy individuals. Additionally, the study reported severe periodontal disease was more prevalent in patients with Alzheimer’s disease than in controls. However, in another study no significant differences were found in patients with periodontal probing depths >4mm in either group of subjects (diseased versus healthy).
Leira et al suggests that chronic periodontal infections may contribute to the onset of dementia via ulcerated periodontal pockets which provide access to systemic circulation. Leira et al also notes that periodontal pathogens are capable of invading multiple cell types allowing for immune evasion and replication in the host tissues. This is supported by evidence of spirochetes being detected in 93.7% of Alzheimer’s disease patients brain tissue. Regarding the meta-analysis Liera et al states, “our meta-analysis showed that patients diagnosed with severe periodontal disease had almost a threefold risk of developing Alzheimer’s disease.”
Nevertheless, some researchers believe that periodontal disease and Alzheimer’s disease have a bidirectional relationship. This is proposed as many patients with Alzheimer’s disease present with poor oral hygiene and may miss dental appointments as they are unable to attend. As you can imagine this lack of care could easily lead to periodontal infection.
Limitations to this study include the small number of studies included and a lack of associated measures allowing only three studies to be included in the meta-analysis. Additionally, due to the study design (case control and cross-sectional) a causal link cannot be established.
The authors conclude by stating, “Evidence available from this systematic review suggests an association between PD and AD. Due to the designs of the included studies, it is not possible to infer any causal association as the time sequence is not defined although an association has been found to be present. We recommend that future studies use either a case-control design with incident cases or a retrospective cohort design. It would be of paramount interest to introduce a question on antecedents of PD at the moment of diagnosis of AD. Further studies should avoid the cross-sectional design, a suboptimal approach in which no causal inference can be made.”
- Leira Y, Domínguez C, Seoane J, Seoane-Romero J, Pías-Peleteiro JM, Takkouche B, Blanco J, Aldrey JM. Is Periodontal Disease Associated with Alzheimer’s Disease? A Systematic Review with Meta-Analysis. Neuroepidemiology. 2017;48(1-2):21-31. doi: 10.1159/000458411. Epub 2017 Feb 21. PMID: 28219071.