The role of inflammation and the gut microbiome in depression and anxiety

Abstract

The study of the gut microbiome has increasingly revealed an important role in modulating brain function and mental health. In this review, we underscore specific pathways and mechanisms by which the gut microbiome can promote the development of mental disorders such as depression and anxiety. First, we review the involvement of the stress response and immune system activation in the development of depression and anxiety. Then, we examine germ‐free murine models used to uncover the role of the gut microbiome in developing and modulating pertinent activity in the brain and the immune system. We also document multiple pathways by which stress‐induced inflammation harms brain function and ultimately affects mental health, and review how probiotic and prebiotic treatments have shown to be beneficial. Lastly, we provide an overview of gut microbiome‐derived compounds (short‐chain fatty acids, tryptophan catabolites, microbial pattern recognition) and related mechanisms (vagal nerve activity and fecal microbiota transplants) involved in mediating the influence of the gut microbiome to mental health. Overall, a picture of the gut microbiome playing a facilitating role between stress response, inflammation, and depression, and anxiety is emerging. Future research is needed to firmly establish the microbiome's causal role, to further elucidate the mechanisms by which gut microbes influence brain function and mental health, and to possibly develop treatments that improve mental health through microbiotic targets.

Differential and spatial expression meta-analysis of genes identified in genome-wide association studies of depression

“…We provide evidence that neurons are enriched for expression of candidate depression risk genes than expected by chance. Our findings highlighted enteric neurons, supporting previous associations between the gut microbiome and mental health 53 . Furthermore, integration of the depression GWAS results and transcriptomic data from brain and non-brain tissues found enrichment in the colon 7 .…”

Evidence of the Importance of Dietary Habits Regarding Depressive Symptoms and Depression

“…Lassale et al [43] meta-analysis demonstrated that avoiding a pro-inflammatory diet was associated with a lower risk of depression, supporting the results of the present study. The available research on the relationship between inflammation, intestinal flora, and mental illness such as depression and anxiety has been studied in systematic literature [47]. The result showed that probiotics (intake of good bacteria) and prebiotics (food for the good bacteria) lead to improved intestinal health, which can reduce inflammation and thus result in fewer symptoms of mental illness [47].…”

“…The available research on the relationship between inflammation, intestinal flora, and mental illness such as depression and anxiety has been studied in systematic literature [47]. The result showed that probiotics (intake of good bacteria) and prebiotics (food for the good bacteria) lead to improved intestinal health, which can reduce inflammation and thus result in fewer symptoms of mental illness [47]. Foods with a pro-inflammatory effect should be avoided for preventive purposes before and in case of mental illness.…”

Functional Neuroimaging in Psychiatry—Aiding in Diagnosis and Guiding Treatment. What the American Psychiatric Association Does Not Know

“…Overgrowth of certain bacteria or yeast species can damage the tight-junctions of the lining of the gastrointestinal (GI) tract leading to abnormal serum levels of polysaccharides and other molecules normally confined to the intestinal tract. Inflammatory responses within the GI tract can lead to pathological irritation of the vagus nerve with resulting depressive symptoms (79,80). GI tract inflammation appears to also be capable of inducing CNS inflammation (79).…”