Lower oral microbiome diversity linked to poorer cognition in schizophrenia patients
A new study from Japan suggests that the health of the oral microbiome may play an important role in cognitive function among people with schizophrenia, highlighting a growing scientific interest in the oral-brain connection.
Researchers from the Institute of Science Tokyo investigated whether reduced diversity of oral bacteria could be associated with worse cognitive performance in individuals with schizophrenia. Their findings indicate that patients with the condition tend to have less diverse oral microbiomes, which may contribute to poorer cognitive outcomes.
The research team proposed that inflammation or disruptions in essential microbial functions caused by low microbiome diversity might influence brain health and cognitive ability. While previous studies have focused mainly on the gut microbiome in schizophrenia, this work shifts attention to the mouth as another critical 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 recognised,” said Takehiro Tamura, Assistant Professor at the Institute of Science Tokyo.
To explore this relationship, the researchers compared 68 patients diagnosed with schizophrenia with 32 unaffected individuals. Cognitive performance was assessed using the full-scale intelligence quotient (FSIQ), a standard measure in which higher scores reflect better cognitive function. Saliva samples were collected from all participants and analysed using rRNA gene sequencing to determine the diversity of their oral microbiomes.
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The results showed a clear association between oral microbiome diversity and cognitive performance. Patients with schizophrenia had both lower FSIQ scores and reduced microbial diversity compared with healthy participants. Within the schizophrenia group, individuals with less diverse oral microbiota demonstrated poorer cognitive function.
“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 mechanistic studies and intervention research, including oral hygiene measures, prebiotics, and probiotics.”
The findings point to potential new strategies for supporting mental health through oral care. While the study does not prove causation, it suggests that maintaining a healthy and diverse oral microbiome could become part of broader approaches to managing cognitive symptoms in schizophrenia.
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The study was published in the journal Schizophrenia Bulletin, reinforcing the importance of interdisciplinary research linking dentistry, microbiology, and neuroscience. Experts say further research is needed to understand whether improving oral hygiene or modifying oral microbiota can directly influence cognitive outcomes in psychiatric disorders.
This emerging evidence strengthens the case for viewing oral health as a key component of overall and neurological health, rather than as a separate or isolated concern.
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