woman holding stomach

Discussions of the mind-body connection rarely focus on the relationship between intestinal problems and mental health. Instead, they focus on how factors such as nutrition and exercise can improve mental health. While this is a valid perspective, it’s not the only way physical concerns can influence psychological well-being.

For example, multiple studies suggest that organisms in the digestive system play a role in the development various mental health disorders. These include anxiety disorders, depressive disorders, schizophrenia, and other mental health conditions.

The Influence of the Gut-Brain Axis

Over the years, researchers gained greater insights into the connection between GI health and mental wellness. That’s why they coined the term gut-brain axis to describe the interconnected nature of these two systems.

As described in a 2015 article in the journal Annals of Gastroenterology, the gut-brain axis (GBA) “consists of bidirectional communication between the central and the enteric nervous system, linking emotional and cognitive centers of the brain with peripheral intestinal functions.”

This internal communication network includes several structures, such as:

  • Brain and spinal cord
  • Central nervous system (CNS)
  • Autonomic nervous system (ANS)
  • Enteric nervous system (ENS)
  • Hypothalamic pituitary adrenal (HPA) axis

Hormones and other neurotransmitters travel in both directions through this network. They deliver messages from the gut to the brain and vice versa.

Experts estimate that as many as 100 trillion microscopic organisms live in the human digestive system. The majority of these are bacteria. Although bacteria are associated with infections and other health problems, a July 2023 Psychology Today article reports most bacteria in the human gut is beneficial.

Helpful bacteria perform vital functions. They help break down food, promote an active immune system, synthesize vitamins, and defend against toxins.

“About 90 percent or more of our gut bacteria are supposed to be good bacteria,” the author of the Psychology Today article wrote. “If more than about 10 percent of our gut bacteria are bad bacteria, then we have what is called ‘dysbiosis,’ or an imbalance of the gut microbiome.”

Intestinal Problems and Mental Health: Anxiety & Depression

In a September 2017 review in the journal Clinics and Practice, a team of experts from Texas Tech University explored the relationship between dysbiosis and symptoms of anxiety and depression.

The authors of this review noted that the gut biome can be impacted by a variety of factors. These include genetics, diet, environment, exposure to stress, and health status. Factors also include seasonal fluctuations and the presence of antibiotics.

When these factors lead to gastrointestinal inflammations, this can prompt the release of an overabundance of neurotransmitters and proteins called cytokines.

  • Two types of cytokines can lead to increased permeability in the blood-brain barrier: TNF-a and MCP
  • This, in turn, can allow rogue molecules to pass from the gut to the brain.
  • Research associates some rogue molecules with various forms of psychological distress, including anxiety, depression, and memory problems.

The Texas Tech team referred to a 2013 study during which healthy individuals with no history of depression received infusions of a toxin that caused GI inflammation and triggered a release of TNF-a cytokines. A significant percentage of subjects developed what the researchers called “classical depressive symptoms.”

However, when healthy subjects received TNF-a cytokines directly, they did not develop depressive symptoms. The researchers concluded the combination inflammation and cytokine release – not the cytokines alone – increased depression risk.

Cytokines can also affect the hypothalamic pituitary adrenal (HPA) axis. The HPA regulates hormone release during times of stress. The Texas Tech group reported that problems within the HPA axis represent “one of the most reliable biological readouts in major depression and anxiety.”

Gut Microbiome & Schizophrenia

In addition to association with two of the most common forms of mental illness – anxiety and depression – research links gastrointestinal abnormalities with more complex mental health concerns, such as schizophrenia.

A March 2020 mini review in the journal Frontiers in Psychiatry reported on the state of research into the connection between the gut microbiome and schizophrenia. Highlights of this report, conducted by a team from the University of Oxford, include the following:

  • At publication, researchers identified six studies that investigated the gut microbiome
  • Consistent findings included “a significant elevation” in a bacteria called Lactobacilli
  • Lactobacilli predicted increased risk of schizophrenia, and also correlated with symptom severity
  • People with schizophrenia often show elevated levels of several cytokines. These include IL-6, IL-8, and TNF-a
  • People with schizophrenia show reduced levels of the anti-inflammatory cytokine IL-10.
  • Experts believe dysbiosis may contribute to a greater likelihood of GI inflammation. This can cause bacterial infections potentially linked to schizophrenia.

Although the team that conducted this mini review did not find overwhelming evidence to support a connection between dysbiosis and schizophrenia, they acknowledged that current findings may lead to future improvements in treatment, and they also indicate the need for additional research.

“Despite limited evidence, there is promise in the use of pre/probiotics as auxiliary treatments in schizophrenia, aimed at improving side-effects of antipsychotics and complementing their action, particularly in terms of cognitive impairments,” they wrote.

Intestinal Problems and Mental Health: Implications for Treatment

Currently, mental health conditions such as anxiety, depression, and schizophrenia are typically treated with a combination of medications and therapy. Depending on which disorder a person has, and how severe their symptoms are, the medication component of care may include one or more of the following:

  • Antidepressants such paroxetine, fluoxetine, and sertraline
  • Mood stabilizers such as lithium and valproic acid
  • Antipsychotics such as aripiprazole, clozapine, and risperidone

Research into the connection between dysbiosis and mental illnesses could lead to the identification of medicines that can address the problem from the gut side of the gut-brain axis.

The authors of the September 2017 Clinics and Practice article that we cited earlier in this post discussed this likelihood. Studies involving both humans and mice, they reported, found that certain probiotics can help the body regulate the HPA axis and reduce the number of pro-inflammatory cytokines in the gastrointestinal area.

“Studies have shown that probiotics effectively mitigated anxiety and depressive symptoms similar to conventional prescription medications …” they wrote. “Advantages include ease of availability, lower cost, less dependence, and fewer side effects compared to pharmaceutics.”

However, they acknowledge that considerable research remains to be done before such an approach is taken to treat mental illnesses. Among the many reasons why additional study is necessary, they wrote, is that the impact of long-term use or high doses of probiotics on the human body is has not yet been effectively researched.

“Until more evidence behind the use of probiotics as therapy for anxiety and depressive disorders is available, probiotics in any form cannot be considered a reliable therapy to anxiety and depressive disorders as compared to psychiatric medications,” they wrote. “Furthermore, gender differences as well as comorbidities such as obesity, lifestyle, and tobacco and alcohol use may impact the overall benefit of probiotics.”