What is already known
The causes of depression are poorly understood, and although the gut microbiota has been linked to depressive symptoms, the underlying biological mechanisms remain unclear. What’s more, both the microbiota and depressive symptom levels vary across ethnic groups.
What this research adds
In one study, researchers studied the microbiotas of more than 3,200 people from six ethnic groups and identified a microbial signature that was associated with depressive symptoms and didn’t vary across the groups. In a second study, researchers analyzed the gut microbiota of about 1,000 people from the Netherlands and found 13 microbial taxa associated with depressive symptoms. Most of these microbial taxa are involved in the production of chemical messengers linked with depression. The findings were then replicated in the European participants of the first study.
Conclusions
The findings support the link between gut microbes and depression, and suggest that the gut microbiota can be a target for future therapies.
Depression affects more than 320 million people worldwide and is a leading cause of mortality. Now, two studies have identified specific gut bacteria that are involved in the production of chemical messengers linked with the condition.
The findings, published in Nature Communications, suggest that the gut microbiota can be a target for future therapies against depression.
Previous studies have associated gut microbes with depressive symptoms, but the causes of depression as well as the underlying biological mechanisms that link the condition to the gut microbiota remain unclear. What’s more, both the microbiota and depressive symptom levels vary across ethnic groups.
To investigate the link between gut microbes and depression, two teams of researchers — one led by Jos Bosch at the University of Amsterdam and the other led by Robert Kraaij and Najaf Amin at the Erasmus Medical Center Rotterdam — set out to analyze the gut microbiota of more than 4,000 people from six different ethnic groups living in the Netherlands.
Depression link
In one study, researchers studied the microbiotas of 3,211 people from Dutch, South-Asian Surinamese, African Surinamese, Ghanaian, Turkish and Moroccan ethnic groups. They found that most bacterial taxa associated with depressive symptoms belong to the Firmicutes phylum, with a prominent presence of Christensenellaceae, Lachnospiraceae and Ruminococcaceae. Less frequent phyla included Bacteroidetes and Proteobacteria.
The microbial signature associated with depressive symptoms was largely invariant across the ethnic groups studied, the researchers found.
“The study findings identified potential targets for psychobiotic interventions that warrant further investigation, and may positively impact depression and well-being at an individual or population level,” the authors say.
Chemical messengers
In the second study, researchers analyzed the gut microbiota of 1,054 people from a different cohort in the Netherlands. The team found 13 microbial taxa associated with depressive symptoms, confirming the association of Eggerthella, Subdoligranulum, Coprococcus as well as bacteria from the Ruminococcaceae family, and identifying new associations with bacteria including Sellimonas, Lachnoclostridium, Hungatella and Ruminococcus. The findings were then replicated in the European participants of the first study.
Most of the bacteria identified are known to be involved in the production of chemical messengers such as glutamate, serotonin and gamma amino butyric acid (GABA). Serotonin and GABA are both relevant to depression, and glutamate levels in the blood and brain tissue have been linked to psychotic disorders.
Although the clinical relevance of the findings needs to be confirmed, the two studies support the link between gut microbes and depression. “These studies provide confirmation of an existing hypothesis that other authors had previously explored, namely the possibility that people with depression may have a different microbiota,” says Rosa del Campo at the Ramón y Cajal Hospital, who was not involved in either study. “The implication of this work is that we should add the gut microbiota as another factor in the cause of depression.”
