Gut microbiota variations in depression and anxiety: a systematic review.

Objective: The aim of this study is to investigate the characteristics of gut microbiota in depression and anxiety through a systematic review.

Methods: Articles were searched in the PubMed, Embase, and PsycINFO databases from their inception to February 12th, 2023. Case-control studies on the characteristics of gut microbiota in depression and anxiety were included. Methodological quality assessment of included studies was performed using the Newcastle-Ottawa Scale (NOS). A qualitative synthesis was conducted to assess bacterial diversity (α- and β-diversity) and taxa abundance differences at the phylum, family, and genus levels.

Results: A total of 24 articles were included in the systematic review, 20 studies were conducted in China. Our results showed that the findings of the α- and β-diversity assessments were inconsistent for both depression and anxiety. In gut microbiota composition, we found that depression and anxiety were characterized by an enrichment of pro-inflammatory bacteria and a depletion of anti-inflammatory SCFAs-producing bacteria. Specifically, Actinobacteria, Proteobacteria, Rikenellaceae, Porphyromonadaceae and Bifidobacteriaceae were more abundant in the depression group, as well as Firmicutes, Prevotellacea and Ruminococcaceae in lower abundance. In the anxiety group, the abundance of Firmicutes, Lachnospira, Faecalibacterium, Sutterella, and Butyricicoccus was lower, while the abundance of Bacteroidetes, Enterobacteriaceae, and Fusobacterium was increased.

Conclusions: The systematic review found that depression and anxiety might be characterized by an enrichment of pro-inflammatory bacteria and the depletion of anti-inflammatory SCFAs-producing bacteria. However, there were conflicting reports on the abundance of bacteria due to confounders such as diet and psychotropic medications. Further studies are strongly suggested.

Clinical trial number: Not applicable.