Can the bacterial community that lives in your gut actually be related to psychiatric illnesses such as schizophrenia and bipolar disorder? Research on the human microbiome and its effects on health and illness has exploded into the worlds of medicine and research. It is increasingly clear that the microorganisms in the human intestinal tract, and the genes produced by all of these microscopic living things, play critical roles in an individual’s patterns of overall wellness — far beyond helping us digest food effectively.

Microbiota and Microbiome Defined

Microbiota is the ecological community of microorganisms (mostly bacteria, but also fungi, viruses, and so on) that live in a particular location, such as your gut. Microbiome refers collectively to the genes harbored in these microorganisms. Researchers must understand the patterns of both the organisms and the genes to help clarify the roles these microscopic creatures play in the body’s health and function. So, if you read something about the microbiome that’s about only the bacteria and not the genes, you know it is an incomplete discussion. Also, while most of the discussions are about the gut microbiota and microbiome, humans actually have colonies of microorganisms living in other areas in and on their bodies, including their skin, reproductive tract, and the mouth and throat (which are technically part of the gut but sometimes are not thought of in that way).

A study in the journal Brain, Behavior, Immunology (May 2017), entitled “The microbiome, immunity, and schizophrenia and bipolar disorder,” summarizes some of the current research looking at the microbiome as it relates to schizophrenia and bipolar disorder. The article reports that many studies in animal models have shown that the gut microbiome could affect thinking and behavior through effects on the immune system. Some human studies have shown that people with psychiatric conditions took antibiotics more frequently than people without these disorders. Humans take antibiotics to kill off unwanted bacterial infections, but these medications also kill off some of the microbiota, changing the person’s microbiome. The question that comes up then is whether these microbiome changes were related to the development of the psychiatric conditions. This article also points to studies that found different microbiota in the mouths and throats (oro-pharyngeal microbiota) of people with schizophrenia compared to those without.

Babies are born with “sterile” guts; they don’t have any gut microbiota. But in the birth process, microorganisms colonize the baby’s mouth and intestine, starting off their process of building a microbiome that eventually looks like an adult’s. Many researchers are exploring how the developing microbiome might affect the developing brain and nervous system. While it seems clear that there are effects, the exact processes mediating the effects and what exactly gets changed or affected remains very unclear. While the immune system is thought to be one pathway, other mechanisms are also being investigated.

Many other areas of research show promising results when looking at the microbiota, microbiome, and illness. Autism researchers are looking at the “gut-microbiome-brain” connection, and there are strong indicators that the microbiota and microbiome have some relationship to autism. Obesity — not a mental illness but of concern to so many people living with mental illness — has been shown to have some very interesting connections to the microbiota in mouse studies. Changing the patterns of bacteria in mouse guts can transform the mouse from lean to obese and vice versa without changing diets. A study from China last month in the World Journal of Gastroenterology reports a case of a 20-year-old with Crohn’s disease and seizures. They treated her with fecal microbiota transplantation — giving her the gut microbiota of a healthy person — and her gastrointestinal symptoms and seizures improved significantly.

The potential benefits to understanding how the microbiota and microbiome interact with the brain and central nervous system could be enormous. Understanding microorganism mechanisms that increase the likelihood of mental illness such as bipolar disorder or neurodevelopmental condition like autism would make room to build new interventions that target those mechanisms. The research in these areas is still in early stages, and there is much more to do, but this is an intriguing and promising story in the quest to understand and treat disorders of the brain.