Depression is the most prevalent mental disorder in industrialized societies. The relationship between the human gut or microbiota – a collection of bacteria, archaea, protists, fungi, and viruses – and mental health is an interesting and controversial topic that has mostly been explored in animal studies.
A research team from Belgium reviewed the microbiomes of 1,054 Belgians to assess a “normal” microbiome. Some in the group scored poorly on a quality of life survey or were diagnosed with depression. Researchers compared their microbiomes with the rest of the group and found that two kinds of microbes, Coprococcus and Dialister, were missing from their microbiomes. This was true regardless of other factors that influence the microbiome, including age, sex, and antidepressant medication use. The team also found that depressed people had an increase in Bacteroides enterotype 2 – bacteria prevalent in those with Crohn’s disease,
To validate their results, the researchers then looked at the microbiomes of 1,070 Dutch people and found that the same two microbes were also missing among those who were depressed, including those with severe clinical depression.
How do gut bacteria link to mood? One possible route is the body’s longest nerve, the vagus nerve, which runs from the brainstem to the intestines and is thought to be a two-way highway, sending signals for digestion from the brain to the gut and back again. In their attempt to link bacteria to mental health, the authors searched the literature for 56 gut-brain modules. They found that Coprococcus seemed to have a pathway associated with dopamine, a key signal involved in depression.
The researchers note that the lack of the two microbes may be either a cause or effect of depression and that further studies are needed. However, other microbiologists have already voiced their optimism about the Belgian team’s findings in recent related articles in magazines such as Science:
Emma Allen-Vercoe, a professor of microbiology at the University of Guelph in Ontario, …believes that Coprococcus and Dialister could be great candidates to use as psychobiotics or probiotics that target mental health. Finding a way to grow these microbes so they could be administered to patients would be “far from trivial,” but she hopes scientists can eventually introduce the bacteria into human guts of and examine the results.
Valles-Colomer, M., Falony, G., Darzi, Y., Tigchelaar, E. F., Wang, J., Tito, R. Y., … & Claes, S. (2019). The neuroactive potential of the human gut microbiota in quality of life and depression. Nature microbiology, 1.
Photo by Cristian Palmer on Unsplash.
