Periodontitis and incident cognitive decline and dementia: a 15-year prospective cohort study of older men residing in Northern Ireland

Background
Periodontitis is a chronic bacterial infection that elicits systemic inflammation. While retrospective studies have linked periodontal pathogens with Alzheimer's disease (AD) and dementia, few have combined cognitive assessments, pathogen exposure, and inflammatory markers.

Objective
To investigate the longitudinal risk between periodontitis, cognitive impairment and dementia.

Methods
We examined the relationship between periodontitis and onset of mild cognitive impairment (MCI) and dementia over 15.6 years (SD 1.6) in older men from Northern Ireland enrolled in the PRIME-COG cohort, using logistic regression. We also assessed associations between exposure to periodontal pathogens and blood inflammatory markers.

Results
Among 642 men, baseline periodontitis was not significantly associated with later onset of dementia and/or MCI (severe versus mild/none, OR 0.83, 95% CI 0.45–1.50, p = 0.923). However, having more teeth predicted lower risk (OR 0.95, 95% CI 0.91–0.99, p = 0.023). Dementia and/or MCI was associated with higher serum IL-6, IL-8, and IFN-γ at baseline, and IL-8 and TGF-β at follow-up. IgG levels to periodontal pathogens remained stable in men who developed dementia and/or MCI but declined in cognitively normal men. A positive correlation between IgG to periodontal pathogens and proinflammatory cytokines was observed in men who developed dementia and/or MCI.

Conclusions
Clinical periodontitis was not associated with dementia or MCI onset, but tooth retention was protective. Elevated inflammatory markers in affected men suggest systemic inflammation may contribute to cognitive decline. Larger, more diverse cohort studies are needed to clarify the role of periodontal disease in dementia and AD risk.