Researchers at the Institute of Science Tokyo have found a connection between oral microbiota diversity and cognitive performance in individuals with schizophrenia. The study, published in Schizophrenia Bulletin on November 27, 2025, involved analyzing saliva samples and cognitive test scores from 68 patients with schizophrenia and 32 healthy controls.
The research team, led by Assistant Professor Takehiro Tamura, Associate Professor Genichi Sugihara, Professor Hidehiko Takahashi, Assistant Professor Yujin Ohsugi, and Professor Sayaka Katagiri, investigated whether disruptions in oral bacterial communities might relate to cognitive impairment. They used the Wechsler Adult Intelligence Scale-Fourth Edition and the Japanese Adult Reading Test to measure cognitive ability. Oral microbiota was characterized using 16S rRNA gene sequencing, while microbial functions were predicted using PICRUSt2.
The results indicated that patients with schizophrenia had less diverse oral bacterial communities compared to healthy individuals. These patients also performed worse on cognitive tests. Within the group with schizophrenia, lower microbial diversity was linked to lower full-scale intelligence quotient (FSIQ) scores. Additionally, an imbalance was observed in key bacterial groups among patients: there was a higher ratio of Streptococcus to Prevotella and changes in other prominent genera.
Further analysis suggested that predicted microbial functional pathways related to glycan biosynthesis, energy metabolism, and cofactor production were positively associated with cognitive performance. Markers of inflammation measured through the kynurenine pathway did not show evidence of mediating this association.
"In people with schizophrenia, lower oral microbiota diversity was associated with poorer cognitive performance, and certain metabolism- and glycan-related functional pathways (PICRUSt2-predicted) were suggested to be potentially involved in this relationship," said Tamura.
The study suggests that changes in oral microbiota are linked to cognitive dysfunction among people with schizophrenia. This points to the potential for exploring oral care or microbiome-targeted approaches as possible interventions for cognitive impairment.
"This study offers a new perspective on the oral–brain axis and lays a foundation for future mechanistic studies and intervention research, the latter including studies of oral hygiene measures, prebiotics, and probiotics," Tamura added.
