Serotonin (5-hydroxytryptamine, 5-HT) is a chemical found in the human body.
It carries signals along and between nerves - a neurotransmitter. It is mainly found in the brain, bowels and blood platelets.
Serotonin is thought to be especially active in constricting smooth muscles, transmitting impulses between nerve cells, regulating cyclic body processes and contributing to wellbeing and happiness.1
Serotonin is regarded by some researchers as a chemical that is responsible for maintaining mood balance, and that a deficit of serotonin leads to depression.
The word serotonin comes from its discovery when it was isolated in 1948 by Maurice M. Rapport and initially classified as a serum agent that affected vascular tone.1
This Medical News Today article provides essential information on serotonin. The article is also available in Spanish.
Contents of this article:
You will also see introductions at the end of some sections to any recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Fast facts on serotonin
Here are some key points about serotonin. More detail and supporting information is in the main article.
- Serotonin is an important chemical neurotransmitter in the human body.
- It is commonly regarded as a chemical that is responsible for maintaining mood balance.
- Serotonin is created by a biochemical conversion process.
- Serotonin is manufactured in the brain and the intestines. The majority of the body's serotonin, between 80-90%, can be found in the gastrointestinal tract.
- Serotonin that is used inside the brain must be produced within it.
- It is thought that serotonin can affect mood and social behavior, appetite and digestion, sleep, memory and sexual desire and function.
- An association has been made between depression and serotonin. Scientists remain unsure whether decreased levels of serotonin contribute to depression or depression causes a decrease in serotonin levels.
- Drugs that alter serotonin levels have important clinical uses such as in the treatment of depression, nausea and migraine.
- Medical research continues to evaluate the role of serotonin in obesity and Parkinson's disease.
- Other ways to increase body serotonin levels include mood induction, light, exercise and diet.
What is serotonin?2
Serotonin is created by a biochemical conversion process which combines tryptophan, a component of proteins, with tryptophan hydroxylase, a chemical reactor. Together, they form 5-hydroxyltryptamine (5-HT), also referred to as serotonin.
Serotonin is most commonly believed to be a neurotransmitter, although some consider the chemical to be a hormone.
Where does serotonin come from?2,3
Serotonin is manufactured in the brain and the intestines. The majority of the body's serotonin, between 80-90%, can be found in the gastrointestinal (GI) tract. It can also be found in the blood platelets and the central nervous system (CNS).
As serotonin can be found widely across the body, it is believed that the chemical plays a role in influencing a variety of body and psychological functions.
Serotonin cannot cross the blood-brain barrier, therefore, serotonin that is used inside the brain must be produced within it.
What does serotonin do?2,3
As a neurotransmitter, serotonin relays signals between nerve cells (neurons), regulating their intensity.
Serotonin is a neurotransmitter, regulating signals between neurons.
Serotonin is widely believed to play a key role in the central nervous system, as well as in the general functioning of the body and in particular the GI tract. Studies have found links between serotonin and bone metabolism, breast milk production, liver regeneration and cell division.
Functions of serotonin
As a neurotransmitter, serotonin influences both directly and indirectly the majority of brain cells. The following is a list of things that it is thought that serotonin could affect:
- Bowel function. Most of the body's serotonin is found in the gastrointestinal tract where it regulates bowel function and movements. It also plays a part in reducing the appetite while consuming a meal.
- Mood. It is most well know for its role in the brain where it plays a major part in mood, anxiety and happiness. Illicit mood-altering drugs such as Ecstasy and LSD cause a massive rise in serotonin levels.
- Clotting. Its third major role is in the formation of blood clots. Serotonin is released by platelets when there is a wound, and the resulting vasoconstriction (narrowing of the tiny arteries - arterioles) reduces blood flow and aids the formation of blood clots.
- Nausea. If you eat something that is toxic or irritating, more serotonin is produced in the gut to increase transit time and expel the irritant in diarrhea. This increase in blood serotonin levels also causes nausea by stimulating the nausea area in the brain.
- Bone density. Studies have shown that a persistent high level of serotonin in the bones can lead to an increase in osteoporosis.2
- Sexual function. Low serotonin levels in the intoxicated state are thought to contribute to the associated increase in libido, while those taking medication that increase serotonin levels are seen to have a reduction in libido and sexual function.3
On the next page we look at the link between serotonin and depression and we examine SSRIs and their role in treating depression. On the final page we discuss some natural ways to boost serotonin levels.