Psyche and the Bowels

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Chronic stress causes harm

Excitement can cause diarrhea; ongoing problems at work or in the family can lead to stomach pain. Frequent nausea or heartburn may also be stress-related. But how exactly are psychological strain and digestion connected?

Why does stress affect an organ system so strongly when it largely functions autonomously? As a reminder: the digestive system is controlled by the enteric nervous system. It coordinates the digestive muscles and regulates the release of digestive secretions and nutrients. The brain is hardly involved in these processes.

Things change, however, when stressors act on the body. The brain then takes over central control and activates the »fight-or-flight« system. All bodily functions which are not immediately necessary for survival are reduced, and the focus shifts to an ideal supply of muscles and brain.

Whether it is a dangerous predator standing in front of us or an upcoming exam that makes us nervous — the brain does not distinguish between the two. It interprets both as acute stress and shuts down the digestive system.

More specifically: the sympathetic nervous system reduces the activity of the stomach and intestines, ensuring that no sensation of hunger arises. Mild nausea often accompanies this. The hypothalamus releases the hormone corticotropin-releasing factor (CRF). CRF inhibits stomach movements. Typical complaints that may arise now include stomach pain or heartburn. At the same time, CRF ensures that the large intestine empties as quickly as possible: intestinal movements increase and more water flows into the colon.

Although both systems are activated during acute stress, the inhibitory effect of the sympathetic nervous system is felt much faster than the hormone release by the hypothalamus. This explains why, in acute danger, digestive symptoms usually do not appear. But during foreseeable, upcoming challenges of modern life, persistent urges to defecate and/or diarrhea are among the most common and unpleasant stress symptoms.

The positive factor about stress-induced gastrointestinal discomfort is that it usually resolves quickly once the exam is over or the holiday trip begins. The situation is different, however, for people affected by chronic stress. If stress levels do not decrease, permanent damage to the digestive system is possible. For example, long-term reduced blood flow to the intestines can promote changes in the intestinal lining and increase the permeability of the gut barrier.

When bacteria penetrate the intestinal mucosa, inflammatory reactions are triggered. The stress hormone CRF also acts directly on immune cells in the intestinal wall, further weakening the gut barrier. In chronic inflammatory bowel diseases, stress-inducing life events — such as losing a job or a breakup — can trigger a disease flare-up. Scientists at the University of Pennsylvania were able to understand the mechanism in mice: after a stressful event, the brain activates the release of glucocorticoids in the adrenal gland.

These act on neurons in the gut as well as the connections between them — the so-called glial cells. Glial cells activate immune cells responsible for inflammation in the intestines. At the same time, the release of glucocorticoids blocks the development of immature intestinal neurons, impairing the signaling pathway responsible for intestinal muscle contraction. As a result, food moves more slowly through the digestive system, intensifying symptoms.

The seeming contradiction — that glucocorticoids are used to reduce inflammation in the treatment of chronic inflammatory bowel diseases, yet promote inflammation during chronic stress — is explained by the duration of exposure. Chronic stress creates a kind of permanent state, whereas treatment aims to be as brief as possible.

It is also considered likely that chronic stress plays a role in the development of irritable bowel syndrome (IBS). Those affected suffer regularly and over long periods from abdominal pain, bloating, diarrhea, or constipation — sometimes so severely that they feel significantly restricted in their everyday life.

Despite the severity of symptoms, no noticeable abnormalities such as those seen in celiac disease or chronic-inflammatory bowel disease are found. Gastroenterologists often observe what is called visceral hypersensitivity. This means affected individuals perceive normal intestinal activity more intensely and unpleasantly than those unaffected.

Responsible for this are pain receptors in the spinal cord. Due to persistent psychological stress or as a consequence of inflammation, they remain permanently activated and falsely signal normal digestive sensations to the brain as a problem.

This triggers a spiral: ongoing digestive issues raise anxiety and stress levels. Anxiety and stress cause stronger intestinal activity, resulting in even more stress. In addition, it is proven that the gastrointestinal tract of people with IBS is more sensitive to stress than of those without the condition. Intestinal movements and abdominal pain become more pronounced.

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