A team of microbiologists has discovered new evidence strengthening the links between gut bacteria and mental health issues such as clinical depression after conducting the first population-level study tackling this subject, which was published Monday.
The team at the Belgian research institute VIB-KU Leuven, led by Jeroen Raes, said in "The neuroactive potential of the human gut microbiota in quality of life and depression" published in the prestigious scientific journal Nature Microbiology that two genera of intestinal bacteria were found to be consistently depleted in individuals with depression, regardless of antidepressant treatment.
"The relationship between gut microbial metabolism and mental health is a controversial topic in microbiome research," Raes explained. "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."
"In our population-level study we identified several groups of bacteria that co-varied with human depression and quality of life across populations," he added, in reference to the Coprococcus and Dialister bacteria that the study found to be reduced in subjects with depression.
In addition, the team saw a positive correlation between quality of life and the potential ability of the gut microbiome to synthesize 3,4-dihydroxyphenylacetic acid, a breakdown product of the neurotransmitter dopamine, which plays a key role in the human brain's reward-motivated behavior.
"Many neuroactive compounds are produced in the human gut," said researcher Mireia Valles-Colomer. "We wanted to see which gut microbes could participate in producing, degrading, or modifying these molecules."
"For example, we found that the ability of microorganisms to produce DOPAC, a metabolite of the human neurotransmitter dopamine, was associated with better mental quality of life," she added.
In order to obtain the data, the authors used DNA sequencing to analyze microbiota in the feces of 1,054 people enrolled in the so-called Flemish Gut Flora Project.
The results were validated in an independent cohort of 1,063 individuals from the Dutch LifeLines DEEP project as well as in a cohort of clinically-depressed patients at the University Hospitals in the Flemish city of Leuven.
Around two percent of adult humans' bodyweight corresponds to bacteria, with many of them located in the gut, meaning that any imbalance in that part of the body can cause complex diseases and ailments such as allergies, obesity or irritable bowel syndrome.