Oral Health and Dementia: Causal Inference and Theoretical Mechanisms.

Area of Science:

• Neuroscience
• Public Health
• Gerontology

Background:

• The causal link between oral health and dementia remains debated, with concerns about reverse causality and unmeasured confounders.
• Essential oral functions like eating and speaking are under-explored as potential mechanisms linking oral health to dementia.
• Social isolation is a recognized modifiable risk factor for dementia.

Purpose of the Study:

• To review how recent epidemiologic studies address criticisms regarding oral health and dementia causality.
• To propose future research directions for establishing a causal relationship.
• To explore novel mechanisms, including social isolation via impaired oral functions.

Main Methods:

• Analysis of studies using repeated surveys and methods for bidirectional relationships to address reverse causality.
• Discussion of quantitative bias analysis (E-value) and methods like fixed-effect analysis and instrumental variables to handle unmeasured confounding.
• Review of theoretical frameworks considering life-course, direct, and indirect dementia mechanisms.

Main Results:

• Studies are increasingly addressing reverse causality, but often fail to incorporate prior cognitive function.
• Methods to control for confounding are underutilized, yielding mixed results.
• Impaired eating and speaking due to poor oral health may increase dementia risk through social isolation.

Conclusions:

• Poor oral health is potentially a modifiable risk factor for dementia, possibly mediated by social isolation.
• Methodologically and theoretically robust studies are crucial for confirming causality.
• Future research should integrate causal inference methods and explore life-course mechanisms, including social aspects of oral function.