Gut Bacteria Tied to Depression

Megan Brooks

February 11, 2019

For the first time, a population-based study has shown a link between gut bacteria and mental health, providing the strongest support to date that microbiota can influence mood, investigators note.

"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," Jeroen Raes, PhD, from University of Leuven and VIB Center for Microbiology, Belgium, said in a news release.

"In our population-level study we identified several groups of bacteria that co-varied with human depression and quality of life across populations," said Raes.

The study was published online February 4 in Nature Microbiology.

Link to Depression

In analyzing data from 1054 individuals enrolled in the Flemish Gut Flora Project (FGFP), investigators found two groups of bacteria — Coprococcus and Dialister — were consistently depleted in people diagnosed with depression, regardless of antidepressant treatment.

They validated the results in an independent cohort of 1063 individuals from the Dutch LifeLines DEEP cohort and in a group of patients with treatment-resistant major depressive disorder.

They also found that Faecalibacterium and Coprococcus bacteria were consistently associated with higher quality of life indicators. Both bacteria produce butyrate, a short-chain fatty acid that strengthens the epithelial defense barrier and reduces intestinal inflammation, and both have been reported to be depleted in association with inflammatory bowel disease and depression.

Using an analytical framework, the researchers created the first catalog of human gut bacteria that have "neuroactive" potential. Some bacteria were found to have a broad range of these functions. For example, the ability of microorganisms to produce 3,4-dihydroxyphenylacetic acid, a metabolite of the human neurotransmitter dopamine, was associated with better mental quality of life.

Diet as Treatment?

Commenting on the study for Medscape Medical News, John Cryan, PhD, principal investigator, APC Microbiome Ireland,
 University College Cork, described the findings as exciting.

"This is a first attempt to link the composition of bacteria in the gut with depression in a large population study. The Flemish data show that there seems to be a reduction in specific bacteria that produce chemicals in depression. Another advantage is the ability to verify some of the same changes in a Dutch cohort and correlate them with quality of life measures," said Cryan.

"The next step will be to identify if the bacteria that are changed are playing a causal role in depression and whether they can be harnessed for psych biotic-based interventions for mood disorders," he added.

Janna Gordon-Elliott, MD, a psychiatrist at Weill Cornell Medicine and New York–Presbyterian Hospital in New York City, also believes the study is noteworthy.

"Everyone is talking about the gut microbiota in medicine across the board for physical medical disorders, and certainly in psychiatry it's all the buzz, but much of the work has been in animal models and a lot of it has also been theoretically based. This study seems to be a really strong step in terms of collecting more clear data from a large-scale human population," Gordon-Elliott told Medscape Medical News.

"What's interesting," she added, "is that they didn't just look at different bacteria species but at which of those species make compounds that act on the brain. These compounds could be cross-referenced as molecules or compounds that are potentially implicated in psychiatric disorders like depression and could then become targets for treatment interventions in the future, whether it be from medications that are developed or from a dietary or nutritional point of view."

The Flemish Gut Flora Project is supported by the Flemish government, Research Fund–Flanders Odysseus program, King Baudouin Foundation, VIB, Rega Institute for Medical Research, and KU Leuven. The authors, Cryan, and Gordon-Elliott have reported no relevant financial disclosures.

Nat Microbiol. Published online February 4, 2019. Abstract

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