1. What is serotonin?
Serotonin acts as type of chemical known as a neurotransmitter. It helps relay signals from one area of the brain to another. Although serotonin is made in the brain, where it performs its main functions, some 90% of our serotonin supply is found in the digestive tract and in blood platelets.
2. How is serotonin made?
Serotonin is made in a unique biochemical conversion process. It starts with tryptophan, a building block for proteins. Cells that make serotonin use tryptophan hydroxylase, a chemical reactor which, when combined with tryptophan, forms 5-hydroxytryptamine (5-HT), otherwise known as serotonin.
3. What role does serotonin play in our health?
Serotonin helps to relay messages from one area of the brain to another. It’s believed to influence a variety of psychological and other bodily functions. Most of our 40 million brain cells are influenced either directly or indirectly by serotonin. They include brain cells related to:
- Sexual desire and function
- Memory and learning
- Temperature regulation
- Some social behaviour
In addition, serotonin can affect the workings of our cardiovascular system, muscles and various parts of the endocrine system. Researchers have also found evidence that serotonin may play a role in regulating the production of breast milk and that a defect within the serotonin network could be one underlying cause of cot death or SIDS ( sudden infant death syndrome).
4. What is the link between serotonin and depression?
Research suggests that an imbalance in serotonin levels may influence mood and may lead to depression. Possible causes include:
- Low brain cell production of serotonin
- A lack of receptor sites able to receive the serotonin that is made
- Inability of serotonin to reach the receptor sites
- A shortage in tryptophan, the chemical that serotonin is made from
If any of these biochemical glitches occur, researchers believe it can lead to depression, as well as obsessive-compulsive disorder (OCD), anxiety, panic and even excess anger.
One theory about how depression develops involves the regeneration of brain cells. This is a process that some believe is mediated by serotonin, and continues throughout our lives. The theory suggests depression may occur when there is a suppression of new brain cells and that stress is the most important precipitator of depression. It’s thought that common antidepressant medications known as SSRIs (selective serotonin reuptake inhibitors), which are designed to boost serotonin levels, help kick off the production of new brain cells, which in turn allows the depression to lift.
Although it is widely believed that a serotonin deficiency plays a role in depression, there is no way to measure its levels in the living brain. Therefore, there have not been any studies proving that brain levels of this or any neurotransmitter are in short supply when depression or any mental illness develops.
However, levels of serotonin in the blood are measurable and have been shown to be lower in people who suffer from depression. However, researchers still don't know if serotonin levels in the blood reflect levels in the brain. They also don't know whether the dip in serotonin causes the depression, or the depression causes serotonin levels to drop.
Antidepressant medications that work on serotonin levels - SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin and norepinephrine reuptake inhibitors) - are believed to reduce symptoms of depression, but exactly how they work is not yet fully understood.