Researchers have linked mental health problems such as depression to deficiencies of two specific gut microbes, in the first population-level research on the relationship between mental health and the gut microbiome, according to Science Daily.

The study examined data from the gut microbiomes of 1,054 people involved in the Flemish Gut Flora Project, along with depression diagnoses from general practitioners. They found that individuals with depression had lower levels of two types of bacteria, Coprococcus and Dialister.

They also found that Coprococcus, and another bacteria called Faecalibacterium, were more common in those that reported better mental quality of life.

Further analysis of two other populations confirmed those findings.

The researchers noted that the study does not prove causality – depression could affect the microbes inside the gut, rather than the other way around. However, they performed follow-up experiments, studying the genomes of over 500 bacteria, that showed gut microbes can affect neuroactive compounds produced in the gut.

The results were published Monday in the journal Nature Microbiology.

“We studied whether gut bacteria in general would have a means to talk to the nervous system, by analyzing their DNA,” said the study’s lead author, Jeroen Raes, Professor at the Catholic University of Leuven in Belgium and the Flemish Institute of Biotechnology.

“We found that many can produce neurotransmitters or precursors for substances like dopamine and serotonin.”

The researchers are now planning another round of microbe sampling from the Flemish Gut Flora Project for further research. Raes said the researchers are still unsure whether these compounds can reach the brain from the gut, or whether they could act on the vagus nerve in the intestines, which itself can communicate with the brain.

They also note some limitations of the study, including that it only examined European individuals. While the results will likely carry over to western nations like the US, they might differ in places like Africa with drastically different diets.

Nonetheless, the study is a substantial step forward in exploring the link between gut microbes and mental health, which, until now, has been largely untested in humans.

According to Raes:

“The relationship between gut microbial metabolism and mental health is a controversial topic in microbiome research. The notion that microbial metabolites can interact with our brain — and thus behavior and feelings — is intriguing, but gut microbiome-brain communication has mostly been explored in animal models, with human research lagging behind.”


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