- Hazan S, von Guttenberg M, Vidal AC, Spivak NM, Bystritsky A. A convenience sample looking at microbiome differences between anxious and non-anxious patients in a GI clinic. Gastroenterol Insights. 2024;15(4):1054–1063. doi:10.3390/gastroent15040072
The cross-sectional study (DOI: 10.3390/gastroent15040072) included 119 patients from a gastroenterology clinic in the USA. The two comparison groups were classified using the GAD-7 questionnaire, in which participants could rate their own level of anxiety. The test group ultimately consisted of 63 participants with mild to severe anxiety scores (GAD-7 ≥ 5) and 56 with low to no anxiety scores (GAD-7 < 5). The participants did not follow any special diet and did not differ significantly in their eating habits.
To analyse the microbiome, bacterial DNA was extracted from stool samples and sequenced.
Both groups were similar in terms of age (average 54 vs. 55 years) and gender. A history of depression and irritable bowel syndrome occurred significantly more frequently in the anxiety group. There was no significant difference in other comorbidities such as ulcerative colitis, autoimmune diseases, Crohn's disease, hypothyroidism or Hashimoto's disease.
Analysis of the gut flora revealed clear differences between the groups. In the anxiety group, the relative frequency of the following bacteria was significantly reduced:
In contrast, Clostridioides and Bacteroides were more prevalent. These differences indicate an altered microbiome structure in anxious individuals, comparable to findings from previous studies on post-COVID syndrome, depression or irritable bowel syndrome.
Previous studies provide evidence that individual bacterial genera may perform specific functions in the interaction between the microbiome and mental health.
For example, the genus Bifidobacterium plays a role in modulating the immune system, the intestinal barrier and the central nervous system. Similar correlations exist for Faecalibacterium, which is associated with lower anxiety levels and better inflammation parameters. A decline in these bacteria could promote neuroinflammatory processes via reduced production of short-chain fatty acids such as butyrate – a possible mechanism in the development of anxiety disorders.
The increased presence of Clostridioides and Bacteroides in the anxiety group has also been linked to poorer quality of life and psychological symptoms in previous studies.
Patients with anxiety were also more likely to have comorbidities such as irritable bowel syndrome and depression. This association supports the assumption of a bidirectional relationship between the gut microbiome, gastrointestinal disorders and mental health conditions.
The present findings are also consistent with studies that documented persistent dysbiosis after COVID-19, especially in long COVID patients with psychological symptoms.
The study provides evidence of altered microbiome composition in patients with self-reported anxiety. At the same time, the authors emphasise that no causal conclusions can be drawn due to the study design. It remains unclear whether dysbiosis is the cause or consequence of anxiety symptoms.
The results are also limited by methodological limitations: small sample size, lack of psychiatric diagnosis, no control of dietary habits, medication or stool transit time, no measurement of SCFA plasma levels.
Although the results of this pilot study support the hypothesis that the gut microbiome is associated with anxiety, further research is needed. Future studies with larger and more ethnically diverse populations, longitudinal design and controlled recording of influencing factors such as nutrition and medication use are necessary to more accurately determine the role of individual microbiota in the development and treatment of anxiety disorders.