Understanding How Mental Health Influences IBD Outcomes: A Review of Potential Culprit Biological Mechanisms.

Inflammatory bowel disease (IBD) includes Crohn's disease (CD) and ulcerative colitis (UC). Similar to other chronic diseases, IBD is associated with negative mental health outcomes. The prevalence of anxiety and depression with IBD is increasing in western societies and there is a growing body of evidence suggesting a bidirectional relationship which remains poorly understood. This review seeks to distil current evidence on the epidemiology, biological mechanisms and microbial changes through which anxiety and depression may lead to worse IBD outcomes. The literature demonstrates that a prior diagnosis of depression is associated with an increased risk of developing IBD. Co-morbid anxiety or depression doubles the odds of adverse outcomes in IBD. Antidepressants appear to have class dependent effects on modulating disease activity in IBD with co-morbid depression. Chronic stress may drive IBD through a number of mechanisms, including inducing the hypothalamic pituitary axis, glucocorticoid resistance, increasing intestinal permeability, and releasing inflammatory cytokines. Alterations in the microbiome on either a genus or species' level has been shown to be affected by and have an impact on both mental health illness and IBD activity. Further research with high quality longitudinal follow-up data is required to clarify causal associations of anxiety/depression and IBD onset as well as measure the impact of different antidepressant classes and microbiome targeted strategies on disease progression and outcomes.