The concept of a communication line between the brain and the gut, referred to in scientific literature as the ‘brain-gut axis’, has been a popular topic in medical research in recent years.
Microbes residing within the human gut are, in many ways, essential to functions of the body but advances in understanding of the influence that the microbial community has on health has led to their implication in a number of conditions. These include obesity, diabetes, and even some forms of cancer.
Among others, mental health has surfaced as a feature of human wellbeing that is under the influence of gut microbial metabolism. A new study published in Nature Microbiology by a group led by Professor Jeroen Raes of the Flanders Institute for Biotechnology and the Catholic University of Leuven has followed this line of reasoning.
Focusing specifically on depression, the researchers studied the correlation between gut microbiome features and the quality of life and depression in 1,054 individuals who constitute the Belgian Flemish Gut Flora Project population cohort.
Mental wellbeing was assessed by means of medical tests and GP records, as well as through self-reporting by participants.
Faecalibacterium and Coprococcusbacteria were found to be consistently more common in individuals experiencing a higher quality of life and mental health.
Conversely, participants living with depression were found to harbour depleted levels of Dialister and Coprococcus bacteria, regardless of whether or not they were prescribed antidepressants.
“This is the first time this kind ofwork has been done in such a large scale in humans. Most previous work has been done in animal models,” said Professor Raes.
Interestingly, bacterial DNA analysis from fecal samples in a subset of the cohort indicated that some bacterial species may be able to produce neurotransmitters such as dopamine and serotonin that communicate with the brain.
Individuals experiencing treatment-resistant depression were found to harbour microbiomes that may be less disposed to generating these molecules. This is particularly intriguing considering the common imbalance of dopamine and serotonin in brains of depressed patients.
“We don’t yet know whether the 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.The findings by Raes and his colleagues are preliminary, providing evidence for a correlation between the gut microbiome and mental health which will require follow-up studies in animals to determine the exact relationship.
Raes explained, “our goal would be to isolate these specific bacteria and culture them in animal models to see if they elicit or change behavioural traits. If this is proven then the next step would be to set up human trials to see if procuring these bacteria can improve symptoms in people with depression.”
Further considerations for researchers involved in this work are the potentially diverse results that may be gathered by considering the microbiomes of individuals in different geographical locations.
While the present findings are applicable to the European community, it would be pertinent to investigate the effects that different diets worldwide may have on the types of bacterial species within the gut.
The present results cannot be interpreted in terms of causality. However, in the event that future research supports the role of gut microbiota in mental wellbeing, clinical approaches to treating mental illness may incorporate personalised probiotics which balance the cohabitation of bacterial species.
Ken Duckworth M.D., medical director of the National Alliance on Mental Illness, stated, “this is a creative and holistic approach to the complex human biology of depression. We need to follow every thread that relates to depression spanning genetics, imaging, psychotherapy and more novel angles such as this. I look forward to learning more about this work.”
Image credit: The unnamed via Flickr