The human microbiome is made up of microorganisms like eukaryotes, fungi, viruses and bacteria. Together they outnumber human cells 10 to 1. There are 1000 more genes in the microbiome than the human genome. The body cannot function without the microbiome. Microorganisms work in sync with the body to keep all systems functioning properly, including the digestive and immune systems. The gut has the highest number of bacteria in the body. A new research review summarizes connections found between the microbiome and immunity and their potential effects on schizophrenia and bipolar disorder.
The gut and the brain are connected by what is called the enteric nervous system. While the ENS can act independently, it can also influence the central nervous system. It does this through millions of neurons as well as neurotransmitters like serotonin, dopamine, glutamate and norepinephrine. When one of these systems dysfunctions, it can heavily impact the other, causing symptoms of depression and anxiety. One way the digestive system can dysfunction is with an alteration in the gut’s microbiome.
The immune system is also vulnerable to changes in the microbiome. The function of the immune system is basically to determine whether microorganisms present in the body are beneficial or harmful. Part of the immune response to harmful microorganisms is inflammation. This inflammation occurs throughout the body, including areas around the brain, which can trigger or worsen symptoms of bipolar disorder.
Faith Dickerson of the Stanley Research Program in Baltimore, Maryland and her team recently reviewed the available research regarding the microbiome, immunity and how they relate to schizophrenia and bipolar disorder. The results will be published in the journal Brain, Behavior and Immunity. Here is what they found:
- A study on the diversity of the microbiome of the throat found that people with schizophrenia had 400 times the population of lactic acid bacteria than than their healthy counterparts. The same study found that some metabolic pathways for siderophores, glutamate, and vitamin B12 were also different in those with schizophrenia. They also found that the biodiversity of the microbiome was larger in the healthy controls.
- Another study also found that the organism Lactobacillus phage phiadh was significantly more abundant in patients with schizophrenia. This microorganism has been tied to diabetes, which is common in people with schizophrenia. It was also found that none of those taking the drug valproate (Depakote) had Lactobacillus phage phiadh in their pharynx when tested, compared to the 17 of 35 individuals not taking the drug.
- Some individuals with bipolar disorder and schizophrenia have consistent, low-grade inflammation associated with dysfunction in the gut microbiome.
- Crohn’s Disease is associated with the yeast Saccharomyces cerevisiae. One study found that some people with schizophrenia and bipolar disorder have elevated levels of antibodies for this organism, especially those with gastric distress.
- There is some evidence that some people with schizophrenia and bipolar disorder have sensitivities to lactose and gluten and that ingestion of these can lead to inflammation.
- One study found that those hospitalized with acute mania had more recent exposure to antibiotics, suggesting an increased rate of bacterial infections in comparison with healthy controls.
The research of the association of gut bacteria with psychiatric disorders is fairly new, but consistently finds connections between gut flora and mental illnesses. Future research may continue to confirm this and possibly lead to more treatment options.
Image credit: National Institute of Allergy & Infections Diseases
*Edit: This article previously stated that levels of Lactobacillus phage phiadh were higher in patients taking the drug valproate. The article cited instead indicates the levels were zero. This article has been modified to reflect that finding.
The article has also been edited to reflect that Saccharomyces cerevisiae is a yeast, not a bacterium.