Abstract and Introduction
Background: Psychiatric co-morbidities including depression and anxiety are common in inflammatory bowel diseases (IBD). Emerging evidence suggests that interactions between the gut microbiota and brain may play a role in the pathogenesis of psychiatric symptoms in IBD.
Aim: To review the literature on microbiota-brain-gut interactions in gut inflammation, psychosocial stress and mental disorders and to discuss the putative mediating role of gut microbiota in the development of psychiatric symptoms or co-morbidities in IBD.
Methods: A literature search was conducted on Ovid and Pubmed to select relevant animal and human studies reporting an association between IBD, mental disorders and gut microbiota.
Results: Gut microbial alterations are frequently reported in subjects with IBD and with mental disorders. Both have been associated with reduced faecal bacterial diversity, decreased taxa within the phylum Firmicutes and increased Gammaproteobacteria. In animal studies, microbial perturbations induce behavioural changes and modulate inflammation in mice. Anxiety- and depression-like behaviours in animals can be transferred via faecal microbiota. In humans, modulation of the gut microbiota with probiotics is associated with behavioural and mood changes. Recent data show correlations in changes of faecal and mucosal microbiota and psychological distress in patients with IBD independent of disease activity.
Conclusion: Both IBD and mental disorders are associated with gut microbial alterations. Preclinical and preliminary human studies have shown a mediating role of the gut microbiota in intestinal inflammation and anxiety, depression and stress. Targeting the gut microbiota may represent a useful therapeutic approach for the treatment of psychiatric co-morbidities in IBD.
The association between inflammatory bowel diseases (IBD) including Crohn's disease and ulcerative colitis (UC) and mental health disturbances is not a new observation. Research articles and review papers examining the relationship date back as early as 1938. In the middle of the last century, IBD were considered classical psychosomatic diseases. The research focus has since shifted towards genetic, immunological, environmental and microbial factors as key factors involved in disease pathogenesis of IBD. Nonetheless, the importance of psychological factors in IBD is mirrored by persistently high numbers of publications, which recently began to consider associations between psychological distress and gut microbiota.[4–7] The microbiota, the gut and the brain are connected by means of a multidirectional communication system commonly termed the microbiota-gut-brain-axis, which enables the brain to influence the composition of the intestinal microbiota, and in turn the microbiota to influence brain and behaviour. Emerging hypotheses suggest that interactions among the microbiota-gut-brain-axis may play a role in the pathogenesis of IBD and mental disorders[10,11] as well as of psychiatric symptoms in IBD patients.[6,7] However, despite the high prevalence of depression and anxiety in IBD patients and their devastating impact on the patients' quality of life, there is still a lack of research on mental health in IBD that addresses the microbiota or the microbiota-gut-brain-axis. In this article, we review the literature on microbiota-gut-brain interactions in intestinal inflammation and psychiatric illnesses and discuss the role of gut microbiota and the microbiota-gut-brain-axis as mediator for psychiatric symptoms in IBD patients.
Aliment Pharmacol Ther. 2020;52(2):247-266. © 2020 Blackwell Publishing