Serotonin

What is serotonin?

Serotonin is a chemical that nerve cells produce. It sends signals between your nerve cells. Serotonin is found mostly in the digestive system (95%), although it’s also in blood platelets and throughout the central nervous system.

Serotonin is made from the essential amino acid tryptophan. This amino acid must enter your body through your diet and is commonly found in foods such as nuts, cheese, and red meat. Tryptophan deficiency can lead to lower serotonin levels. This may result in mood disorders, such as anxiety or depression.

NORMAL RANGE

Normal ranges for serotonin levels

Generally, the normal range for serotonin levels in your blood is 101–283 nanograms per milliliter (ng/mL). This benchmark, however, may differ slightly depending on the measurements and samples tested, so talk to your doctor about specific test results.

High levels of serotonin may be a sign of carcinoid syndrome. This involves a group of symptoms related to tumors of the:

• small intestine
• appendix
• colon
• bronchial tubes

A doctor will take a blood test to measure serotonin levels in your blood to diagnose the disease or rule it out.

Here’s how serotonin acts in various functions across your body:

Bowel movements: Serotonin is found primarily in the body’s stomach and intestines. It helps control your bowel movements and function.

Mood: Serotonin in the brain is thought to regulate anxiety, happiness, and mood. Low levels of the chemical have been associated with depression, and increased serotonin levels brought on by medication are thought to decrease arousal of mood.

Nausea: Serotonin is part of the reason why you become nauseated. Production of serotonin rises to push out noxious or upsetting food more quickly in diarrhoea. The chemical also increases in the blood, which stimulates the part of the brain that controls nausea.

Sleep: This chemical is responsible for stimulating the parts of the brain that control sleep and waking. Whether you sleep or wake depends on what area is stimulated and which serotonin receptor is used.

Blood clotting: Blood platelets release serotonin to help heal wounds. The serotonin causes tiny arteries to narrow, helping form blood clots.

Bone health: Serotonin plays a role in bone health. Significantly high levels of serotonin in the bones can lead to osteoporosis, which makes the bones weaker.

Sexual function: Low levels of serotonin are associated with increased libido, while increased serotonin levels are associated with reduced libido.

MENTAL HEALTH

Serotonin and mental health

Serotonin helps regulate your mood naturally. When your serotonin levels are normal, you feel:

• happier
• calmer
• more focused
• less anxious
• more emotionally stable

A 2007 study found that people with depression often have low levels of serotonin. Serotonin deficiency has also been linked to anxiety and insomnia.

Minor disagreements about the role serotonin plays in mental health have occurred. Some researchers in older studies have questioned whether an increase or decrease in serotonin can affect depression. Newer research claims it does. As you can see, it doesn’t make the argument easier whether it does or doesn’t. For example, a 2016 animal study examined mice lacking serotonin autoreceptors that inhibited serotonin secretion. Without these autoreceptors, the mice had higher levels of serotonin available in their brains. Researchers found these mice exhibited less anxiety and depression-related behaviours.

SSRIs

Low levels of serotonin in the brain may cause depression, anxiety, and sleep trouble. Many doctors will prescribe a selective serotonin reuptake inhibitor (SSRI) to treat depression. They’re the most commonly prescribed type of antidepressant.

SSRIs increase the levels of serotonin in the brain by blocking reabsorption of the chemical, so more of it remains active. SSRIs include Prozac and Zoloft, among others.

When you’re taking serotonin drugs, you shouldn’t use other medications without first talking to your doctor. Mixing drugs may put you at risk of serotonin syndrome.