A new study from Japan suggests that the health and diversity of the oral microbiome may play a significant role in cognitive function among individuals with schizophrenia, highlighting a growing scientific interest in the oral-brain connection.

Researchers at the Institute of Science Tokyo examined whether reduced diversity of oral bacteria is associated with poorer cognitive performance in people with schizophrenia.

Their findings indicate that patients with the condition generally have less diverse oral microbiomes, which may contribute to lower cognitive abilities.

The research team proposed that inflammation or disruptions in critical microbial functions caused by low microbiome diversity could impact brain health and cognition. While most previous studies have focused on the gut microbiome, this work emphasizes the mouth as another important site of host-microbe interaction.

“Host-microbiome interactions are not limited to the gut. Like the gut microbiota, the oral microbiota also participates in such interactions. Its significance in systemic and neurological conditions has become increasingly recognized,” said Takehiro Tamura, Assistant Professor at the Institute of Science Tokyo.

The study compared 68 patients diagnosed with schizophrenia to 32 healthy individuals. Cognitive performance was measured using full-scale intelligence quotient (FSIQ) scores, with higher scores indicating better cognitive function. Saliva samples were collected from all participants and analyzed through rRNA gene sequencing to assess oral microbiome diversity.

Results showed a clear link between oral microbiome diversity and cognitive performance. Patients with schizophrenia not only had lower FSIQ scores but also exhibited reduced microbial diversity compared to healthy participants. Within the schizophrenia group, those with less diverse oral microbiota performed worse on cognitive assessments.

“In people with schizophrenia, lower oral microbiota diversity was associated with poorer cognitive performance,” Professor Tamura said. “This study offers a new perspective on the oral-brain axis and lays a foundation for future research on interventions, including oral hygiene, prebiotics, and probiotics.”

Although the study does not establish a direct causal relationship, the findings suggest that maintaining a healthy and diverse oral microbiome could become part of broader strategies to support cognitive health in schizophrenia.

Published in the journal Schizophrenia Bulletin, the study underscores the importance of interdisciplinary research linking dentistry, microbiology, and neuroscience. Experts note that further investigation is needed to determine whether improving oral health or modifying oral microbiota can directly enhance cognitive outcomes in psychiatric disorders.

The research adds to growing evidence that oral health is a key component of overall and neurological wellbeing, rather than an isolated aspect of healthcare.