Gut microbiome in serious mental illnesses: A systematic review and critical evaluation

Abstract

Schizophrenia and bipolar disorder (BD) are associated with debilitating psychiatric and cognitive dysfunction, worse health outcomes, and shorter life expectancies. The pathophysiological understanding of and therapeutic resources for these neuropsychiatric disorders are still limited. Humans harbor over 1000 unique bacterial species in our gut, which have been linked to both physical and mental/cognitive health. The gut microbiome is a novel and promising avenue to understand the attributes of psychiatric diseases and, potentially, to modify them. Building upon our previous work, this systematic review evaluates the most recent evidence of the gut microbiome in clinical populations with serious mental illness (SMI). Sixteen articles that met our selection criteria were reviewed, including cross-sectional cohort studies and longitudinal treatment trials. All studies reported alterations in the gut microbiome of patients with SMI compared to non-psychiatric comparison subjects (NCs), and beta-diversity was consistently reported to be different between schizophrenia and NCs. Ruminococcaceae and Faecalibacterium were relatively decreased in BD, and abundance of Ruminococcaceae was reported across several investigations of SMI to be associated with better clinical characteristics. Lactic acid bacteria were relatively more abundant in SMI and associated with worse clinical outcomes. There was very limited evidence for the efficacy of probiotic or prebiotic interventions in SMI. As microbiome research in psychiatry is still nascent, the extant literature has several limitations. We critically evaluate the current data, including experimental approaches. There is a need for more unified methodological standards in order to arrive at robust biological understanding of microbial contributions to SMI.

The Gut Microbiome in Psychosis From Mice to Men: A Systematic Review of Preclinical and Clinical Studies

“…However, animal studies lacked reporting and should therefore be interpretate carefully. Overall, alterations and lack of reporting can be potential cofounding factors [further extensive review elsewhere (42)]. Methodological difference should be standardised in the future to improve translatability between animal and human studies and would allow for improved interpretation of data.…”

“…Furthermore, we identified potential factors particular to psychosis, which may contribute to the altered gut microbiome. The methodology of the studies covered was not described in details as these were extensively reviewed elsewhere (42). Compared to previous reviews (43) we provide detailed discussion of factors such as antipsychotic use, lifestyle and environmental factors as well as the potential pathological role of the microbiome in psychosis relevant to microbial changes.…”

Effects of dietary supplementation of a probiotic (Bacillus subtilis) on bone mass and meat quality of broiler chickens

“…Probiotics are live microorganisms which confer health benefits in hosts when administered in appropriate amounts ( FAO/WHO, 2001 ). Several studies that investigated the effect of probiotics on human health have reported that probiotics can be used as a bacteriotherapy for a variety of diseases including psychiatric disorders such as major mental illness ( Butler et al., 2019 ; Nguyen et al., 2019 ). Similarly, several probiotics, such as Lactobacillus , Bifidobacterium , and yeasts, have been investigated as diet additives or alternatives to antibiotics for improving production and health in broilers ( Pelicia et al., 2004 ; Alavi et al., 2012 ; Mohammed et al., 2018 ).…”

Comprehensive profiling of the gut microbiota in patients with chronic obstructive pulmonary disease of varying severity

“…Ruminococcaceae abundance has been demonstrated to be significantly lower in non-alcoholic fatty liver disease (NAFLD) patients than non-NAFLD patients [36], and relatively decreased in bipolar disorder [37]. The relative abundance of Lachnoclostridium, Tyzzerella subgroup 4, Flavonifractor, and…”