A healthy gut makes serotonin – but it’s not used to boost your mood

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GUT MICROBIOME

A healthy gut makes serotonin – but it’s not used to boost your mood

BY ACTIVATED PROBIOTICS January 2, 2025

The digestive tract produces serotonin not for the brain to use, but to act locally and promote regular bowel movements. It’s now thought that an imbalance in this hormone may contribute to the development of poor gut health and health concerns such as irritable bowel syndrome (IBS). In this blog article, we discuss the important role of serotonin for gut health and how the gut microbiota may influence gut serotonin balance.

What does the serotonin produced in your gut actually do?

Serotonin is a neurotransmitter and a hormone that is well known for its ability to make people feel happy. In fact, many people have heard that over 90% of the body’s serotonin is produced in the gut and that’s why gut health is so important for mood and mental health. However, the serotonin produced in the gut is actually used by the gut (not the brain) and assists with the function of the digestive system.

The difference between brain-derived and gut-derived serotonin

While it is true that the serotonin released by nerve cells in the brain acts as a neurotransmitter, helping to regulate our mood, the serotonin produced in the gut (gut serotonin) acts as a hormone and plays an important role in a wide variety of mechanical and sensory processes in the gut (1).

Specialised cells in the lining of your digestive tract, called enterochromaffin (EC) cells, produce and release gut serotonin. When gut serotonin binds to receptors on nerve cells in the digestive tract, this helps to stimulate muscle fibres which regulate bowel movements and also help to create signals that allow us to feel sensations such as pain (2).

Gut serotonin and healthy gut function

Normal serotonin balance in the gut helps to promote healthy digestion and prevent digestive concerns like IBS by ensuring that the muscles contract as they should and create regular bowel movements as a result. It also ensures that pain is felt at an appropriate level.

Studies have found that people with digestive concerns like IBS have disturbances in the way serotonin is released in the gut and how long its effects last. This is thought to contribute to irregular and alternating bowel habits and a sensitive digestive tract that more easily feels pain (3).

One of the leading hypotheses that is attempting to explain why this happens suggests that abnormalities in the microorganisms living in the gut (the gut microbiota) may be responsible (3).

The effect of the gut microbiota on gut-derived serotonin

The gut microbiota, and the metabolites that it produces, are heavily involved in the regulation of hormones and nerve cells in the gut and have been found to impact gut-derived serotonin. Short chain fatty acids, which are released by gut microbes, influence the rate of serotonin production and release in the gut, and gut microorganisms have been shown to impact how long serotonin will bind to and stimulate nerve cells for (3, 4).

When the gut microbiota is out of balance, which is often observed in patients with digestive concerns and IBS, the balance of serotonin and its effects on gut function can be significantly altered and give rise to uncomfortable symptoms, such as diarrhoea and abdominal pain (3).

Probiotics and gut-derived serotonin

The effects of the gut microbiota on serotonin balance may help to explain why some probiotic strains can offer symptom relief in instances of digestive upset. For example, Lactobacillus rhamnosus GG is a specific probiotic strain that has demonstrated an ability to relieve abdominal pain and promote regular bowel movements in people with IBS. In-vitro studies have shown that these benefits may be, at least partly, due to the effects of this probiotic strain on gut serotonin balance and signalling (3, 6).

Conclusion

The gut is called the body’s second brain, not because of its ability to produce serotonin for the brain to use, but because it also has its own complex nervous system that is needed to keep it functioning well. The serotonin produced by the gut largely stays in the gut and plays a bigger role in maintaining healthy digestion rather than supporting our mental health. Although gut-derived serotonin may have less of an impact on our mood than people think, the gut is really important for our mental health in lots of other ways (due to the gut-brain axis) and you can read more about that here.

REFERENCES

  1. Yadav VK. Chapter 5 – Serotonin: The Central Link between Bone Mass and Energy Metabolism. In: Translational Endocrinology of Bone [Internet]. Elsevier; 2013. p. 51–62.
  2. Cao, Y. N., Feng, L. J., Liu, Y. Y., Jiang, K., Zhang, M. J., Gu, Y. X., Wang, B. M., Gao, J., Wang, Z. L., & Wang, Y. M. (2018). Effect of Lactobacillus rhamnosus GG supernatant on serotonin transporter expression in rats with post-infectious irritable bowel syndrome. World journal of gastroenterology, 24(3), 338–350.
  3. Öhman L, Törnblom H, Simrén M. Crosstalk at the mucosal border: importance of the gut microenvironment in IBS. Nat Rev Gastroenterol Hepatol. 2015 Jan;12(1):36-49. doi: 10.1038/nrgastro.2014.200. Epub 2014 Dec 2.
  4. Reigstad, C. S., Salmonson, C. E., Rainey, J. F., 3rd, Szurszewski, J. H., Linden, D. R., Sonnenburg, J. L., Farrugia, G., & Kashyap, P. C. (2015). Gut microbes promote colonic serotonin production through an effect of short-chain fatty acids on enterochromaffin cells. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 29(4), 1395–1403. 
  5. Pedersen, N., Andersen, N. N., Végh, Z., Jensen, L., Ankersen, D. V., Felding, M., Simonsen, M. H., Burisch, J., & Munkholm, P. (2014). Ehealth: Low FODMAP diet vs Lactobacillus rhamnosus GG in irritable bowel syndrome. World Journal of Gastroenterology, 20(43), 16215.

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