Association of Oral Frailty and Gut Microbiota with Depressive Symptoms: Results of the Cross-Sectional Shika Study

Background/Objectives: Oral frailty (OFr) and gut dysbiosis have each been associated with depressive symptoms (DSs); however, their interactive effects on DSs remain unclear. This study aimed to investigate the combined association of OFr and gut microbiota composition with DSs. Methods: A cross-sectional study was conducted among 277 adults in Shika Town, Ishikawa Prefecture, Japan. OFr was assessed based on number of remaining teeth, difficulty chewing and swallowing, oral dryness, and frequency of tooth brushing. DSs were evaluated using the Center for Epidemiologic Studies Depression Scale (CES-D). Gut microbiota were analyzed using 16S rRNA gene sequencing. Binary logistic regression analysis was performed with DSs as the dependent variable, the interaction term between gut microbiota and OFr as the independent variable, and age, sex, BMI, and drinking and smoking status as covariates. Results: The interaction terms between OFr and Bacteroides (odds ratio [OR] = 1.212; 95% confidence interval [CI] = 1.076–1.366; q = 0.023), Faecalibacterium (OR = 1.191; 95% CI = 1.046–1.357; q = 0.040), Blautia (OR = 1.229; 95% CI = 1.068–1.413; q = 0.030), and Subdoligranulum (OR = 1.310; 95% CI = 1.109–1.547; q = 0.023) remained statistically significant predictors of DSs after FDR correction. Conclusions: Significant interactions between OFr and specific gut microbial taxa were observed even after adjustment for potential confounders and FDR correction. These findings suggest that OFr may be an important factor to consider when investigating the relationship between gut microbiota and DSs.