A new study looking at the gut bacteria of over 1,000 people in Belgium has found a possible link between certain types of bacteria and depression.
The study published in Nature Microbiology combined data from the microbiomes of 1,054 people enrolled in the Flemish Gut Flora project with self-reported and physician-diagnosed depression data. Using bioinformatics analyses, the researchers were able to identify certain groups of bacteria, which were either positively or negatively correlated with mental health.
Two groups of bacteria in particular, Coprococcus and Dialister, were consistently found to be at low numbers in people with depression. The scientists then checked their findings on another cohort of 1,063 people involved in a similar study in The Netherlands and found the same result.
"This is the first time this kind of work has been done in such a large scale in humans. Most previous work has been done in animal models," said Jeroen Raes, Professor at the Catholic University of Leuven in Belgium and Flemish Institute of Biotechnology and lead author of the study.
The research also suggests that some bacterial species in the microbiome may be able to produce or breakdown molecules that interact with the human nervous system. They looked at bacterial DNA from fecal samples in a subset of the study group, finding that the gut microbiome may be able to synthesize molecules such as seratonin and dopamine, which are found in abnormal levels in people with depression. People with treatment-resistant depression had microbiomes that were less-likely to be able to synthesize these molecules than healthy people.
"We don't yet know whether these neuroactive compounds produced in the gut can reach the brain. Can they traverse the blood-brain-barrier? Or perhaps they act directly on the vagus nerve in the intestines, which sends signals directly to the brain," said Raes.