Does pneumonia increase the risk of dementia and cognitive decline? A systematic review and meta-analysis

The link between pneumonia and elevated risk of dementia and cognitive decline is still unclear. This study aims to evaluate the link between pneumonia and the subsequent risk of developing dementia. MEDLINE (<i>via</i> PubMed), EMBASE (Excerpta Medica Database), Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science, Scopus, ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP) databases were searched for studies, published up to 29 February 2024. Eligible studies provided data on adult patients diagnosed with pneumonia and reported outcomes related to dementia or cognitive decline. Quality of observational studies was assessed by the Newcastle-Ottawa Scale. Pooled hazard ratios (HRs) and odds ratios (ORs) with 95% confidence intervals (CI) were calculated using random-effects models. Subgroup analyses were done based on age, geography, study design and pneumonia type. Ten studies were included, encompassing a diverse population sample. Pooled analysis demonstrated a significant correlation between pneumonia and increased risk of dementia (HR = 1.738; 95% CI: 1.358 to 2.225), with substantial heterogeneity across the studies (I² = 97.1%). Subgroup analysis indicated that the association was more pronounced in older adults and varied slightly by region and study design. The risk did not significantly differ between bacterial and non-specific pneumonia types. This meta-analysis suggests that pneumonia is associated with a significantly higher risk of developing dementia. These findings underscore the need for diligent monitoring and preventive strategies for patients recovering from pneumonia, particularly among the elderly, to mitigate potential cognitive decline. PROSPERO registration number: CRD42024520631.