The gut microbiome has an integral role in the maintenance of overall health. Previous research indicates when compared to controls, the composition and function of the gut microbiome vary in patients with schizophrenia; however, it is not evident how these alterations functionally impact individuals with schizophrenia.

According to a recent study published in the Schizophrenia Bulletin, researchers indicated that patients with schizophrenia may possess different intestinal microbiota abundance and beta diversity compared with healthy control individuals, implying that the gut microbiome may play a role in the etiology of schizophrenia.

The researchers conducted a systematic review and meta-analysis to combine and evaluate data on compositional and functional alterations in microbiota in patients with psychosis or schizophrenia. The review contained observational and experimental studies.

From 1990 to July 2021, researchers used PsycINFO, EMBASE, Web of Science, PubMed, MEDLINE, and Cochrane databases and gathered data from human and animal studies reporting on gut microbiota analysis and diversity measures, as well as their clinical implications. Human studies included adults diagnosed with psychosis or schizophrenia, while animal studies focused on fecal microbiota transplant between case and control groups.

Meta-analyses were performed to uncover differences in microbiota diversity, while standardized mean differences (SMDs) and CIs were used to compare diversity indices between patients with schizophrenia and healthy control individuals. The authors indicated 16 studies that included 1,376 patients (748 cases of psychosis/schizophrenia and 628 healthy controls) met the study criteria.

With regard to their results, the authors wrote, “Although observed species and Chao 1 show a decrease in diversity in people with schizophrenia compared with controls (SMD = –0.14 and –0.66 respectively), that did not reach statistical significance. We did not find evidence for variations in richness or evenness of microbiota between patients and controls overall. Differences in beta diversity and consistent patterns in microbial taxa were noted across studies.”

The authors also indicated that they discovered abundance increases in Bifidobacterium, Lactobacillus, Megasphaera, and Veillonella being the most frequently reported in the psychosis/schizophrenia group versus control individuals, while decreases were most commonly reported in Coprococcus and Streptococcus. They also noted that variations in brain structure, metabolic pathways, and symptom severity might be correlated with compositional alterations in the microbiome, and the heterogeneous design of studies complicates a comparable evaluation of functional readouts.

The researchers found no evidence of variations in intestinal microbiota between patients with psychosis or schizophrenia and control individuals; however, beta diversity was meaningfully different between psychosis and schizophrenia groups compared with control individuals.

Based on their findings, the authors wrote, “The existing evidence suggests that the microbiome may play a role in the etiology, pathology, and symptomatology in schizophrenia.”

Finally, the authors noted, “Understanding how predicted or functional alterations in microbial genes or metabolic pathways influence symptomatic expression and downstream clinical outcomes may contribute to the development of microbiome-targeted interventions for psychosis.”

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