Oral Microbiome Changes Linked to Mental Health Disorders Across Six Conditions

This groundbreaking systematic review and meta-analysis examined oral microbiome alterations across six mental health conditions, analyzing data from 20 case-control studies involving patients with autism spectrum disorder (ASD), schizophrenia, major depressive disorder, alcohol use disorder, obsessive-compulsive disorder, and panic disorder.

The research addresses a critical gap in understanding how oral bacteria—the body's second-largest microbial community—may contribute to mental health. While gut microbiome research has established the gut-brain axis, oral microbiota's role in mental disorders remained largely unexplored despite offering superior diagnostic accessibility through simple saliva sampling.

Key findings revealed significantly higher microbial diversity in patients compared to healthy controls, with a Simpson Index showing standardized mean difference of 0.42. Each condition displayed unique bacterial signatures: ASD patients showed Rothia enrichment, schizophrenia patients had overrepresentation of hydrogen sulfide-producing genera, and depression patients exhibited reduced Solobacterium and Leptotrichia levels. Beta diversity analysis revealed significant variations only in schizophrenia and major depressive disorder.

These condition-specific microbial patterns suggest oral microbiota could serve as accessible biomarkers for mental health diagnosis and treatment monitoring. The oral sampling advantage over gut microbiome analysis—requiring only saliva collection rather than stool samples—makes this approach particularly promising for clinical applications. The findings support the emerging concept of an oral-brain axis, complementing established gut-brain connections in mental health pathophysiology.