Researchers at Science Tokyo have reported a link between oral health and cognitive function in people with schizophrenia. Their study suggests that lower diversity in oral bacteria may be associated with poorer cognitive performance.
The study, published in Schizophrenia Bulletin on November 27, 2025, analyzed saliva samples and cognitive test scores from 68 patients with schizophrenia and 32 healthy controls. Cognitive ability was measured using the Wechsler Adult Intelligence Scale-Fourth Edition and the Japanese Adult Reading Test, summarized by full-scale intelligence quotient (FSIQ).
Researchers found that patients with schizophrenia had less diverse oral microbiota and performed worse on cognitive tests. Within the patient group, lower microbial diversity was linked to lower FSIQ scores. They also observed an imbalance in key bacterial groups, with a higher Streptococcus-to-Prevotella ratio and other shifts in prominent genera.
Using a computational tool called PICRUSt2, the team predicted microbial functional pathways, finding that those related to glycan biosynthesis, energy metabolism, and cofactor production were positively associated with cognitive performance. However, markers of the kynurenine pathway—a measure of neuroinflammation—did not appear to mediate this relationship.
Assistant Professor Takehiro Tamura, lead author, explained: “Lower oral microbiota diversity was associated with poorer cognitive performance, and certain metabolism- and glycan-related pathways may be involved.”
The study highlights the oral microbiome as an accessible window into microbial states linked to cognition. While cross-sectional and exploratory, the findings provide testable hypotheses for future research, including studies on oral hygiene interventions, prebiotics, and probiotics.
“This work offers a new perspective on the oral–brain axis and lays the groundwork for mechanistic and interventional studies,” Tamura added.