The Gut – Brain Axis and Its Role in Mental Health Presentations in IBD

In January 2021 my UC symptoms returned, this time more serious. I was in the toilet 20 times a day, blood and mucous in my stools, significant weight loss and severe abdominal pain. I was admitted to hospital for the first time at the beginning of February, the week I was due to start my Health Psychology internship with the University of Auckland. Oral steroids helped the symptoms gradually subside and the gastroenterologist suggested I begin a biologic drug for longer term use. Over the next 8 months, I was admitted to hospital 6 times with varying degrees of success from biologics and steroids. I was physically and emotionally exhausted. On top of being unwell, I was continuing my degree with a high workload. Thankfully, the University of Auckland and my manager at my internship were supportive, I successfully complete my degree on time in 2022. I am grateful for the support of my husband, who was there with me every step of the way.

I was always curious about how stress could be impacting UC. I was at a significantly stressful point in my life in 2021 –completing my degree, saving for a wedding, living far from home and being in hospital during the COVID-19 pandemic. I asked my gastroenterologist at the time, who told me that there is “little evidence” to suggest that stress plays a part in symptom onset and severity in UC. I struggled to believe this given my background in Health Psychology and my interest in how the mind and body are constantly in sync.

Driven by personal experience and professional interest, I completed a literature review and gave a presentation on the Gut – Brain Axis. I believe that, given the link between the gut and mental stress, it is paramount that professionals working with individuals who have inflammatory conditions such as IBD understand the importance of the Gut – Brain Axis and its role in Mental Health. The communication between the central nervous system (CNS) and gut is referred to as the gut – brain axis. The autonomic nervous system, hypothalamic-pituitaryadrenal (HPA) axis, and nerves within the gastrointestinal (GI) tract link the gut and the brain. This system allows the brain to influence intestinal activities, and the gut to influence mood. Increasing evidence has associated an imbalance in the gut and CNS with symptomatology in gastrointestinal diseases such as Inflammatory Bowel Disease (IBD) while healthy gut function has been linked to regulated CNS function.

The brain and the gut are connected physically and biochemically. Physically, the gut and the brain are connected via the nervous system, in particular the Vagus nerve. Messages are continuously sent between the two. When the gut experiences disturbance, like in IBD, a message is sent to the brain that there is dysfunction. The brain interprets this as a stressor, eliciting the body’s stress response via the sympathetic nervous system. Part of the stress response is the secretion of the hormone cortisol. Cortisol has been found to increase intestinal permeability, influencing various GI disturbances seen in IBD (cramping, leaky gut, mucous). Following GI disturbance from cortisol, neural signals are then passed back to the brain, signalling disturbance, and this stress response is perpetuated.

The gut and the brain are also connected biochemically. Biochemical information from the gut is carried to the body and brain by cytokines (inflammatory proteins), neurotransmitters, and hormones. Inflammatory cytokines elevate inflammation in the body, as seen in IBD. Elevated inflammation can create the stress response, leading to increased levels of cortisol, thus increasing an individual’s experience with symptoms. This relationship between the gut and inflammation plays a significant role in the perpetuation of mental health stress, through the HPA response and the role of the gut – brain axis.

The gut microbiome plays an integral part in this system. The composition of our microbiome influences intestinal permeability. A healthy microbiome forms a strong intestinal tissue, thus protecting the body from release of inflammatory. An unhealthy microbiome, disrupted by inflammation as well as by cortisol, leads to a more permeable intestinal wall allowing for the passing through of cytokines and pathogens into the blood vessels. These in turn activate the body’s stress response cycle, maintaining inflammation in the body and possible chronic stress.

To understand the role that the gut – brain axis plays in mental health, numerous studies have demonstrated that both acute and chronic stress interfere with intestinal barrier and induce adverse alterations in the gut microbiome. A disrupted barrier allows for pathogens and inflammatory cytokines to pass into the blood vessels, which cause systemic inflammation, resulting in the HPA stress response. If a person is under chronic stress from environmental factors, this cycle is constant. Presumably due to this cycle of systemic inflammation, the gut –brain axis has been implicated in several mood disorders. Anxiety and depression have well –established links to functional GI disruption. This link between GI disruptions and mood disorders is primarily due to the inflamed gut sending messages to the brain, resulting in the afore mentioned stress response. Interestingly, individuals with a diagnosis of depression have been found to have increased levels of inflammatory cytokines in the blood. When a person experiences a chronic stress response (as in mood disorders) they experience symptoms, such as fatigue, appetite disturbance, difficulty in concentrating and apathysymptoms also seen in IBD. As mentioned above, when the gut is disrupted by the stress response, the intestinal wall becomes more permeable, allowing the release of these cytokines into the blood. The body then reacts with a systemic inflammatory response. Research has demonstrated that inflammatory cytokine activates the HPA axis, hence contributing to the presentation of mental health issues in patients with gut related issues.

In conclusion, one cannot say for sure that environmental stress does not play a factor in symptoms of IBD due to the close link between inflammation in the gut and the stress response. It is paramount for Health

Professionals working with IBD patients to understand this link and empower patients to manage their stress to soothe the Gut – Brain Axis, hence helping to reduce the perpetuation of the inflammatory system response.