Bidirectional impact of dementia and aspiration pneumonia on cognitive decline in older adults: A retrospective cohort analysis

Aim Dementia and aspiration pneumonia are common and debilitating conditions in older adults. While both are significant contributors to morbidity and mortality, the interaction between these conditions remains inadequately understood. This study aimed to explore the bidirectional relationship between dementia and aspiration pneumonia and to assess its impact on cognitive decline in older patients. Methods A retrospective cohort analysis of 500 elderly dementia patients at a tertiary care center (2018‐‐2022) was conducted, and participants were classified by aspiration pneumonia occurrence. Cognitive function was assessed via the Mini‐Mental State Examination (MMSE) at baseline and follow‐up, with Kaplan–Meier analysis evaluating time‐to‐pneumonia and Cox regression modeling of bidirectional relationships while adjusting for confounders. Results Among 500 dementia patients (mean age 78.3 ± 7.2 years), Kaplan–Meier analysis revealed significantly earlier pneumonia onset in severe dementia patients (log‐rank P < 0.001), with Cox regression showing that severe dementia conferred triple the pneumonia risk (hazard ratio [HR] = 3.01, 95% confidence interval [CI]: 2.15–4.21) and that swallowing dysfunction independently increased the hazard ratio 3.45‐fold (95% CI: 2.61–4.55); aspiration pneumonia accelerated cognitive decline (β = −2.35, 95% CI: −3.12 to −1.58). Conclusion This study revealed that dementia severity substantially increases time‐dependent pneumonia hazard (severe dementia HR = 3.01), while pneumonia accelerates cognitive deterioration, forming a bidirectional cycle amplified by swallowing dysfunction. Early dysphagia management and pneumonia prevention strategies are crucial for disrupting this progression in older adults. Geriatr Gerontol Int 2025; ••: ••–•• .