The Microbiome: Are Trillions of Gut Microbes Controlling our Mental Health?

by Harrison Theriault

Edited by Keren Luo

“Evidence suggests that the gut and its resident microorganisms significantly influence mental health, as well as cognition,” says Christopher Lowry, Ph.D., an associate professor of integrative physiology at the University of Colorado Boulder. Modern technology is beginning to unlock the connection between the brain and the intestinal tract, also called the microbiome-gut-brain axis, while answering a number of questions that have confounded the medical world for years. For example, when someone is prescribed an antidepressant such as an SSRI, or a selective serotonin reuptake inhibitor, it is generally thought to affect the brain’s serotonin paths. Yet, 90 percent of serotonin receptors are not located in the brain but rather in the gut. The question becomes, is the medication affecting the brain or the gut? Once affecting the gut, is it the gut that has a major influence on the brain? (Naidoo, 2018).

A mental health focused, worldwide collaboration among scientists, is studying the bacteria in the intestines to determine if mental illness originates in the gut or anywhere else outside of the brain. Interestingly, there is a growing consensus that a number of mental health disorders that afflict humans are more than a problem of the individual’s brain. Scientists at Tong University of Medicine in China, after evaluating 21 different studies, reported in the Journal of General Psychiatry that the regulation of the balance of the gut’s intestinal bacterial populations is significantly involved in reducing anxiety and a variety of other mental health disorders (Yang, Wei, Ju, & Chen, 2019).

Looking closely at the ecosystem of microbes in the gut, researchers have found that certain species of gut bacteria are missing in people with depression. According to microbiologist Jeroen Raes, reporting in Nature Microbiology, depressed people have lower levels of the bacteria Coprococcus and Dialister, normally found in healthy guts, when compared to those without depression(Valles-Colomer, et al., 2019). Bacteria in the gut microbiome are found to influence brain activity by producing compounds that directly affect and mimic a number of neurotransmitters in certain neural pathways. For example, the bacteria Serratia can secrete dopamines, a neurotransmitter involved in mood disorders. Other microbiotas (gut bacteria) secrete other neurotransmitters; for example, Lactobacillus can secrete acetylcholine, which is important in the regulation of memory, learning, and mood (Liu & Zhiu, 2018).

Accordingly, studies completed at John Hopkins University have recently shown that the gut-brain axis is a communication highway with interactions between the brain and the intestinal tract. Further research is unraveling evidence that the gut-brain signals are disrupted when the normal gut microbiomes are either dominated by unhealthy bacteria or when healthy bacteria are not present. Such signals being sent through the central nervous system trigger a variety of mental changes including mood disorders (The Brain-Gut Connection). When the composition of the microbiomes in the gut change, more serious brain disorders, such as Alzheimer’s disease and related memory loss from conditions such as dementia can manifest. Recently, at the University of Wisconsin’s Alzheimer’s Disease Research Center, Barbara Bendlin, Ph.D., and Frederico Rey, Ph.D. found that Alzheimer’s disease has a unique community of gut microorganisms. Specifically, people with Alzheimer’s disease had lower levels of Bifidobacterium, an important inhabitant of the healthy human gut (Vogt et al., 2018). Furthermore, patients suffering from Alzheimer’s were shown to have a less diverse microbiome with distinct compositional differences compared with the healthy gut (Vogt et al., 2017). Other disorders such as depression reveal a gut profile of microbiota that is also less diverse and less rich than those of healthy individuals (Greenberg, 2018).

What is clear, according to Stanford University School of Medicine, is that the trillions of microbes in the gut control much more in the body than previously thought. These microbes are turning out thousands of new proteins, which are so small that they have gone unnoticed until now (Yang et al., 2019). These proteins fold into unique shapes that have control over key biological functions in the human body. These bacterial proteins are then transcribed into RNA and sent off to the ribosomes for translation, or the creation of proteins (Yang et al., 2019). The gut bacteria appear to be controlling many of the physiological processes that influence a number of the body’s physiological functions.

The manner in which we look at and treat mental illnesses ranging from mood disorders to major psychotic disturbances is now undergoing a major paradigm shift because of this new discovery. This cutting-edge research into mental health issues affected by bacteria has revealed startling revelations as to the origins of mental health issues that afflict one in four Americans. Given the new information that perhaps the origins of mental illness lie outside the brain, mental illness is no longer being considered only a chemical imbalance that originates in the brain. This major news is turning the psychiatric world upside down, as most therapies to date have focused on only treating the brain and influencing the brain’s inner-connections.