Oral Health and Its Association With Gut Microbiota Diversity in Older Post‐Stroke Inpatients

Aim The relationship between oral health and gut microbiota diversity remains unclear, especially in vulnerable populations. We aimed to explore the association between oral health status and gut microbiota diversity in older inpatients recovering from stroke. Methods This cross‐sectional study was conducted in a convalescent rehabilitation ward. Participants were older post‐stroke inpatients. Oral health was assessed using the Revised Oral Assessment Guide (ROAG), with scores ≥ 9 indicating oral problems. Gut microbiota diversity was analyzed by 16S rRNA gene sequencing of fecal samples, and measured using the Shannon index (prespecified primary outcome), richness (observed features/OTUs), and Faith's phylogenetic diversity (PD). Multivariable linear regression analysis was performed to examine the association between ROAG scores and diversity indices, adjusting for potential confounders. Results Participants were 156 older patients after stroke (mean age 78.6 years). Oral problems were present in 121 patients (77.6%). After adjusting for confounders including age, sex, stroke type, comorbidities, and nutritional intake, the total ROAG score was associated with the Shannon index ( B = −0.044, 95% CI: −0.082 to −0.005). In exploratory analyses, no clear associations were found between ROAG scores and richness ( B = −3.774, 95% CI: −7.844 to 0.296) or Faith's PD ( B = −0.087, 95% CI: −0.451 to 0.277). Conclusion In this registry‐based cross‐sectional study, poorer oral health (higher ROAG score) was associated with lower gut microbiota α‐diversity (Shannon index). Given multiple outcomes and no preregistered analysis plan, these findings are exploratory/hypothesis‐generating and require confirmation in independent cohorts and longitudinal studies.