Our understanding of the gut-brain axis has increased significantly in the past decade and is strongly supported by recent research. The bidirectional nature between the gut and brain microbiome interactions has been associated with both the pathophysiology and pathogenesis of irritable bowel syndrome (IBS) and other GI disorders, but there is increasing evidence of psychiatric and neurologic disorders including autism spectrum disorders (ASD), affective disorders, Parkinson's disease, and multiple sclerosis.
The gut microbiota is vital for healthy functioning of the immune system as well as metabolism through the contribution of essential inflammatory mediators, vitamins, and nutrients. Recent studies have shown that the intestinal microbiota can modulate communication between the gut and brain through the nervous, immune, and endocrine systems. If the intestinal microflora is altered, changes can be seen in physical/mental symptoms.
Anxiety is a psychiatric disorder that is often overlooked, especially when it's a comorbid condition. The global incidence of anxiety disorder is 3-25%, and when it occurs in chronic diseases such as cancer, IBS, and cardiovascular disease, it can be as high as 70%. Standard treatment for anxiety is usually psychopharmacological therapies and psychotherapy; however, finding alternative therapies, such as making changes in diet that can also reduce symptoms, would be beneficial to those suffering from anxiety.
Yang and colleagues sought to determine whether anxiety symptoms could be improved by regulation of intestinal microorganisms through a systematic literature review. Out of the 3,334 articles the researchers reviewed, 21 met both the inclusion and exclusion criteria. The 1,503 participants included "patients with IBS (10 studies), healthy controls (six studies) and other patients with chronic diseases such as chronic fatigue syndrome (CFS), rheumatoid arthritis (RA), obesity, fibromyalgia, and type 2 diabetes mellitus." Sixteen studies utilized "interventions regulating intestinal flora" consisting of probiotics with Lactobacillus alone or a mixture of Lactobacillus, Streptococcus, and Bifidobacterium, and five of the studies used "treatment as usual" and probiotics.
This study had significant limitations due to the heterogeneity of comparisons made in the research design types, subjects, interventions, and anxiety assessment scales, eliminating the possibility of a meta-analysis. While there is a possibility that regulating the intestinal microbiota through probiotics and non-probiotic approaches may have a positive effect on reducing anxiety symptoms, further studies need to be performed to definitively make these conclusions.
