Rhinitis, sinusitis, and risk of dementia: A systematic review and meta-analysis.

INTRODUCTION: This study aimed to systematically review epidemiological evidence on the association between rhinitis or sinusitis and the risk of dementia. METHODS: This review followed PRISMA 2020 guidelines and a protocol registered in PROSPERO (CRD420251181185). A comprehensive search was conducted in Medline, EMBASE, CINAHL, and Web of Science databases for literature published up to October 2025. The search strategy incorporated the terms of 'rhinitis' OR 'sinusitis' AND 'dementia' OR 'Alzheimer'. We included cohort, case-control, and Mendelian randomization studies that reported the risk of dementia among adults diagnosed with rhinitis or sinusitis. Three PECO questions were defined to guide data synthesis and the assessment of certainty of evidence using the GRADE approach. Hazard ratios (HRs) or odds ratios (ORs) were pooled using a random‑effects model in the meta‑analysis. Risk of bias was evaluated for each study design. RESULTS: A total of eight articles met the inclusion criteria, all of which were suitable for meta‑analysis. Among the included articles, one article included both a cohort and a case‑control design, resulting in a total of nine study units in the final analysis. Three cohort studies showed an association between rhinitis or sinusitis and all-cause dementia (HR 1.10, 95% CI: 1.09-1.11). However, rhinitis or sinusitis was not significantly associated with Alzheimer's disease in either cohort or case-control analyses. There was no evidence of a relationship between allergic rhinitis and Alzheimer's disease in either cohort or Mendelian randomization analyses. Certainty of evidence ranged from low to very low. Most studies were judged to have a low risk of bias. CONCLUSION: Rhinitis or sinusitis was associated with a modestly increased risk of all-cause dementia in the cohort analysis, but inconsistency and imprecision across studies limit causal inference. Therefore, large-scale observational or Mendelian randomization studies that include diverse populations and encompass both chronic rhinitis and sinusitis are needed. Mechanistic studies are also needed to elucidate whether type 2 immune responses may contribute to neurodegeneration.