Association of Irritable Bowel Syndrome with Dementia: A GRADE-Assessed Systematic Review and Meta-Analysis

Introduction Numerous gastrointestinal (GI) diseases have been linked to an increased risk of dementia. Irritable bowel syndrome (IBS) is a prevalent GI disorder; however, existing studies investigating its association with dementia have reported mixed findings, and no prior meta-analysis has synthesized the available evidence. Methods A comprehensive search of MEDLINE (via PubMed), Scopus, and Web of Science was conducted in August 2025, with no language restrictions, to identify observational studies comparing the risk of all-cause dementia and dementia subtypes (e.g., Alzheimer's disease (AD) in individuals with and without IBS. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using the DerSimonian–Laird random-effects model. The certainty of evidence was assessed using the GRADE approach. Results More than 750,000 participants were included from three cohort and two case-control studies. The pooled analysis showed that IBS was associated with significantly higher odds of all-cause dementia (OR = 1.22; 95% CI: 1.13–1.31; p < 0.00001; I² = 26%), with the overall certainty of evidence rated as high. The association remained robust across all sensitivity analyses. IBS was also significantly associated with higher odds of AD (OR = 1.27; 95% CI: 1.08–1.50; p = 0.005; I² = 64%), with the certainty of evidence rated as low. Conclusion Our findings consistently suggest that IBS is associated with higher rates of dementia outcomes; however, this association is derived from observational data and does not establish causality. Further well-designed prospective studies are needed to clarify the nature of this relationship.