Genetic evidence strengthens the bidirectional connection between oral health status and psychiatric disorders: A two-sample Mendelian randomization study

Background: Observational studies cannot accurately infer the causal associations between oral health status and psychiatric disorders. Methods: We conducted univariate and multivariate Mendelian randomization (MR) analyses using single nucleotide polymorphisms (SNPs) associated with eight oral health statuses (periodontitis, DMFS, Nteeth, toothache, loose teeth, painful gums, bleeding gums, and mouth ulcers) and four psychiatric disorders (Schizophrenia, Major Depressive Disorder (MDD), anxiety and stress-related disorder (ASRD), and Bipolar Disorder (BIP)) as instrumental variables. Genetic data were sourced from the Gene-lifestyle interactions in dental endpoints (GLIDE), UK Biobank, Psychiatric Genomics Consortium (PGC), and Lundbeck Foundation Initiative for Integrative Psychiatric Research (iPSYCH). The inverse variance-weighted (IVW) approach, supported by a comprehensive sensitivity analysis, was employed. Results: Genetically predicted mouth ulcers were significantly linked to higher MDD (OR = 2.17, 95 % CI: 1.33-3.54, P< 0.01) and BIP risks (OR = 2.25, 95 % CI: 1.22-4.15, P = 0.01). BIP heightened bleeding gums risk (OR = 1.01, 95 % CI: 1.00-1.01, P < 0.01). These associations were adjusted for smoking status and alcohol consumption. Painful gums were significantly associated with MDD risk (OR = 96.48, 95 % CI: 2.66-3495.28, P = 0.01), while MDD raised periodontitis risk (OR = 2.15, 95 % CI: 1.24-3.75, P = 0.01), both confounded by smoking and alcohol. Relatively small effects between several variables, while others could not withstand correction for multiple tests. Limitations: The sample size and limitation to European populations limits the study generalizability. Conclusions: This study provide evidence of possible causal relationships between several oral health conditions and mental illness. Focusing on oral health and valuing mental health are important for each other and overall health.