How does serotonin affect the gut?

Neurotransmitters perform an important task in our body: they transmit information between nerve cells. They are active not only in the brain, but also in other parts of the body. For example, about 95% of the neurotransmitter serotonin is found in the intestine, where it makes a decisive contribution to healthy intestinal function.

Effect of serotonin in the intestine

Serotonin is released whenever food enters the small intestine. Then the neurotransmitter stimulates intestinal movements, which ensure that the food moves through the intestine.

Serotonin also reduces your appetite when you eat and signals when you have eaten enough food by making you feel full. In addition, serotonin serves another function that protects the gut [1]: when we eat something we are allergic to or that contains harmful bacteria, the body releases more serotonin, which significantly reduces the number of pathogens [2] and results in increased intestinal motility and faster passage of intolerable food (through diarrhea or even vomiting) out of the body. Conversely, low serotonin levels seem to be related to constipation and other gastrointestinal disorders [3]. Therefore, serotonin-based medications are often used for nausea and vomiting and also for irritable bowel syndrome [4].

What role does serotonin play in irritable bowel syndrome?

Irritable bowel syndrome (IBS for short) is a widespread intestinal disorder that primarily affects the colon. Typical symptoms are flatulence, abdominal pain and cramps, diarrhea or constipation, which occur in episodes and can last for several days, weeks or even months. For the affected patients, irritable bowel syndrome is accompanied by considerable suffering, which often massively impairs their quality of life. However, the cause of the symptoms is not yet clearly understood and diagnosis is difficult.

However, there are indications that serotonin is not only of great importance for normal intestinal function, but also plays an important role in irritable bowel syndrome [5]. Depending on the amount of serotonin in the intestine, the symptoms seem to change: Irritable bowel patients with little serotonin in the intestine often suffer from constipation with rather hard bowel movements, while irritable bowel patients with a high amount of serotonin in the intestine tend to have soft and watery bowel movements and diarrhea [6].

Conclusion on the effect of serotonin on the intestine

By far the largest part of the serotonin present in the body is located in the intestine. There, the neurotransmitter fulfills important tasks such as controlling intestinal movements and protecting the intestine from bacteria or incompatible foods. An imbalance in the serotonin balance can be related to various complaints such as irritable bowel syndrome, which is treated with serotonin-based drugs, among other things.

Sources

[1]https://pubmed.ncbi.nlm.nih.gov/23797870/
[2] https://pubmed.ncbi.nlm.nih.gov/32521224/
[3] https://pubmed.ncbi.nlm.nih.gov/19115522/
[4] https://pubmed.ncbi.nlm.nih.gov/19361459/
[5] https://www.deutsche-apotheker-zeitung.de/daz-az/2000/daz-36-2000/uid-7195
[6] https://www.healthline.com/health/irritable-bowel-syndrome/serotonin-effects#side-effects