One of the most controversial topics in microbiome research is the connection between the gut microbial metabolism and mental health. Advanced sequencing methods have allowed to explore the role of gut microbiota in different neurological and psychiatric diseases, including Alzheimer's disease, Parkinson's disease, depression, etc. Previous studies have investigated communication between gut microbiota and brain in animal models but corresponding human research was lagging behind. Recently, the first population-based study showed a link between gut bacteria and mental health: the Belgian Flemish Gut Flora Project (FGFP) population cohort (n = 1,054) was investigated to assess gut microbiota covariation with quality of life (QoL) indicators and general practitioner-reported depression. The study established a significant covariation of gut microbiota composition with QoL indicators and depression. Coprococcus and Dialister bacteria were depleted in individuals with depression. The presence of Faecalibacterium and Coprococcus were associated with higher QoL indicators. As part of this study, he researchers created the first catalog of human gut bacteria which are associated with neurological conditions. It has been found that the ability of some bacteria to produce 3,4-dihydroxyphenylacetic acid, a dopamine metabolite, is associated with better mental quality of life. This study does not claim to have detected a causal relationship but it shows strong association between the gut microbiome and depression.
Last month, a systematic review of gut microbiota and major depression was published in "Fontiers in Psychiatry". Based on existing human studies, it has found no consensus on which bacteria are most relevant to depression.
1. Valles-Colomer M, Falony G, Darzi Y, Tigchelaar EF, Wang J. The neuroactive potential of the human gut microbiota in quality of life and depression. Nat Microbiol. 2019 Feb 4. doi: 10.1038/s41564-018-0337-x.
2. Cheung SG, Goldenthal AR, Uhlemann AC, Mann JJ, Miller JM, Sublette ME. Systematic Review of Gut Microbiota and Major Depression. Front Psychiatry. 2019 Feb 11;10:34. doi: 10.3389/fpsyt.2019.00034.