Serotonin
and Eva Rudolf-Müller, doctorEva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.
More about the experts All content is checked by medical journalists.Serotonin is a messenger substance that transmits information in our nervous system. Its correct biochemical name is 5-hydroxy-tryptamine, or 5-HT for short. Since it influences our emotions in addition to many other processes, the vernacular calls serotonin "happiness hormone". Read here how it is structured, what effect it has and which diseases lead to an altered serotonin level.
What is serotonin?
Serotonin is a so-called neurotransmitter: It is a messenger substance that in our nervous system passes information from one nerve cell to another. Serotonin is found in both the central and peripheral nervous systems. It is also found in the blood platelets (thrombocytes) and in large quantities in special cells in our gastrointestinal tract.
Serotonin: formation, breakdown and excretion
Most of the serotonin is produced in the so-called enterochromaffin cells of the intestine. However, production also takes place in nerve cells in the brain. Serotonin is made from the amino acid tryptophan. Special enzymes ensure that a hydroxyl group is attached to the tryptophan and a carboxyl group is removed, releasing carbon dioxide - hence the biochemically precise name 5-hydroxy-tryptamine.
The finished serotonin is then stored in small storage chambers, the vesicles, and released from there when required. After it is released, it is taken up again via a 5-HT transporter and partly fed to the storage vesicles and partly broken down. This is done with the help of various enzymes such as monoamine oxidase A (MAO-A). The end product of serotonin breakdown is what is known as 5-hydroxyindole acetic acid, which is then excreted in the urine.
Serotonin action
The serotonin can bind to different receptors on the surface of different cells in the body. Each serotonin receptor leads to a different response in the body. Serotonin controls many different processes. In the central nervous system, for example, serotonin is an important messenger substance that influences a wide variety of processes:
- Body temperature
- appetite
- Emotions
- Central reward system
- Mood and drive
- State of consciousness and sleep-wake rhythm
- Pain assessment
Outside the brain, the messenger substance influences the size of the blood vessels, the bronchi and the intestines. It also stimulates the blood platelets (thrombocytes) and thus plays an important role in blood clotting.
Serotonin: Food affects serotonin levels
Some foods like walnuts and bananas contain serotonin. Chocolate is also said to lead to the release of the "happiness hormone". Unfortunately, the serotonin from food does get into the body, but it cannot cross the natural boundary between the brain and the bloodstream (blood-brain barrier). The feeling of happiness after eating certain foods is more likely to be attributed to a psychological “placebo effect”.
When is serotonin determined?
The serotonin level is mainly determined when the doctor suspects an excess of the hormone due to a disease due to a hormone-producing tumor. Such a carcinoid usually develops in the gastrointestinal tract, but can also develop in other parts of the body. Possible symptoms are:
- Flush (facial flushing and flushing)
- Racing heart
- watery diarrhea
- Cramps (spasms) of the airways (bronchospasms)
Serotonin reference levels
The doctor can determine the serotonin directly from the blood serum or from a 24-hour urine collection. Much more often, however, the determination is made indirectly via the main breakdown product of serotonin - hydroxyindole acetic acid (HIES). It is measured in the 24-hour urine collection: The normal value for HIES is up to 9.0 milligrams in 24 hours (mg / 24 h).
When is the serotonin level lowered?
Some medical professionals suspect that the development of some mental illnesses (such as depression or anxiety disorders) is related to low serotonin levels. So far, however, these have only been theories and no significant evidence has been found so far.
Deficiency of serotonin
If you would like to find out more about how serotonin deficiency develops and what it triggers in the body, read the article Serotonin Deficiency.
When is the serotonin level increased?
An increased amount of hydroxyindole acetic acid (HIES) and therefore serotonin can indicate a carcinoid syndrome in particular. Measurements of more than 40 milligrams of HIES in the 24-hour urine collection are evidence of such a tumor.
An increased HIES level can also occur in epilepsy and celiac disease (sprue).
What to do if the serotonin level changes?
In the case of carcinoid syndrome, the hormone-producing tumor is surgically removed if possible. Alternatively, the patient is treated with so-called somatostatin analogues. The success of the therapy is then checked again by determining the hydroxyindole acetic acid: If the urine reaches normal values again, the serotonin has also decreased.
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