Plain language summary
The gut microbiome has been implicated in several neurological disorders; however exact mechanisms are still not fully understood. This review of recent studies, aimed to investigate the relationship between an imbalanced gut microbiome and depression. The authors first looked at the epidemiology of disease, concluding that significant burden needs to be assessed through improved preventative measures. This will depend upon the correct identification of risk factors, and the study focused on the role of the gut microbiome in this through animal and human studies. Imbalances in inflammation through altered gut microbiota, depleted biodiversity and stress induced microbiome changes were all implicated in the development of depression. It was concluded that studies on the role of microbiota in depression remain promising but are small and follow many different methodologies. This study could be used by healthcare professionals to better understand the role of gut microbiota in the development of depression and that ensuring a healthy gut may improve symptoms.
The human gut microbiome partakes in a bidirectional communication pathway with the central nervous system (CNS), named the microbiota-gut-brain axis. The microbiota-gut-brain axis is believed to modulate various central processes through the vagus nerve as well as production of microbial metabolites and immune mediators which trigger changes in neurotransmission, neuroinflammation, and behavior. Little is understood about the utilization of microbiome manipulation to treat disease. Though studies exploring the role of the microbiome in various disease processes have shown promise, mechanisms remain unclear and evidence-based treatments for most illnesses have not yet been developed. The animal studies reviewed here offer an excellent array of basic science research that continues to clarify mechanisms by which the microbiome may affect mental health. More evidence is needed, particularly as it relates to translating this work to human subjects. The studies presented in this paper largely demonstrate encouraging results in the treatment of depression. Limitations include small sample sizes and heterogeneous methodology. The exact mechanism by which the gut microbiota causes or alters neuropsychiatric disease states is not fully understood. In this review, we focus on recent studies investigating the relationship between gut microbiome dysbiosis and the pathogenesis of depression. This article is based on previously conducted studies and does not contain any studies with human participants or animals performed by any of the authors.