Plain language summary
Alterations to the gut microbiota may be associated with depression and anxiety disorders through a pathway known as the gut-brain axis. Inflammation may be the mediator between the two, as individuals with major depressive disorder (MDD) have reported high levels of inflammation, which the gut microbiota may have the capacity to protect against. This observational study of the gut microbiota of 90 young adults with MDD and 47 healthy controls aimed to determine the relationship between inflammatory gut microbiota and symptoms of depression. The results showed changes to several species of gut microbiota in those with MDD and that the level of change was related to MDD symptom severity. These changes were observed even in those taking psychotropic medications. Changes at the taxonomic level indicated that those with higher symptoms of depression had more pronounced differences compared with healthy controls. Although the observed differences were indicative of an inflammatory microbiome, no changes were observed in blood markers of inflammation between those individuals with MDD and healthy controls. It was concluded that the gut microbiome of individuals with MDD was different from healthy individuals in favour of an inflammatory environment. This study could be used by healthcare professionals to understand that the status of the gut microbiota may be an important measure in individuals with MDD and that a treatment plan to ensure gut health is considered may help with symptoms of depression.
Abstract
We assessed the gut microbiota of 90 American young adults, comparing 43 participants with major depressive disorder (MDD) and 47 healthy controls, and found that the MDD subjects had significantly different gut microbiota compared to the healthy controls at multiple taxonomic levels. At the phylum level, participants with MDD had lower levels of Firmicutes and higher levels of Bacteroidetes, with similar trends in the at the class (Clostridia and Bacteroidia) and order (Clostridiales and Bacteroidales) levels. At the genus level, the MDD group had lower levels of Faecalibacterium and other related members of the family Ruminococcaceae, which was also reduced relative to healthy controls. Additionally, the class Gammaproteobacteria and genus Flavonifractor were enriched in participants with MDD. Accordingly, predicted functional differences between the two groups include a reduced abundance of short-chain fatty acid production pathways in the MDD group. We also demonstrated that the magnitude of taxonomic changes was associated with the severity of depressive symptoms in many cases, and that most changes were present regardless of whether depressed participants were taking psychotropic medications. Overall, our results support a link between MDD and lower levels of anti-inflammatory, butyrate-producing bacteria, and may support a connection between the gut microbiota and the chronic, low-grade inflammation often observed in MDD patients.
Methodological quality
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