Hormones and neurotransmitters are fascinating chemicals that govern a wide variety of bodily functions. As long as they remain in balance, things go well, but too much or too little can cause many unpleasant symptoms and disrupt important biological processes. One of the more important neurotransmitters is serotonin.

What is Serotonin?

Serotonin (5-hydroxytryptamine or 5-HT), first isolated in 1948, is a chemical that acts as a neurotransmitter in the human body. Neurotransmitters are the “messengers” in the nervous system and brain, transmitting signals that cause a variety of different processes such as hormone secretion and muscle activity to occur. Most scientists believe serotonin is a neurotransmitter, while others feel it may be a hormone. Although I knew about serotonin in the brain and its effects on mood, I didn’t realize it was also so important to gut function and other biological processes.

Where Do You Find Serotonin?

Serotonin is found primarily in the brain, bowels and blood platelets. Manufactured by the brain and intestines, 80 to 90 percent of the body’s serotonin is found in the gastrointestinal tract. The brain also produces serotonin, but only for its own use. The body makes serotonin from the amino acid tryptophan by combining it with a chemical reactor called tryptophan hydroxylase. There is a physical barrier between the blood and brain that serotonin cannot cross, which is why the brain produces its own supply.

What Does Serotonin Do?

Research indicates this chemical is important in regulating mood, and that it can affect appetite, digestion, memory, sexual desire and function, sleep and social behavior . People who are depressed often have low serotonin levels, although scientists have not determined whether the low levels are a cause of depression or a result of a depressed mood. Serotonin may also play a role in obesity and Parkinson’s disease. Some drugs used in treating depression, nausea and migraine alter serotonin levels, and serotonin levels in the body can also be increased by diet, exercise, light (such as sunlight) and mood induction – using environmental cues to change people’s moods (Source).

Serotonin transmits or relays signals between nerve cells (neurons) and regulates their intensity. Too much serotonin, which can occur in a condition called serotonin syndrome, can lead to excessive nerve activity and can be life-threatening. Too little serotonin means nerves don’t function at optimum levels. It is difficult for researchers to study serotonin, because it requires the ability to unravel complex biological activities within the nervous system in real time. For example, serotonin in the blood can be measured, but serotonin in the brain cannot be measured, and researchers don’t know whether blood levels reflect levels in the brain.

Diseases and Treatments

Research is currently in progress on the role serotonin plays in Parkinson’s disease, obesity, mood disorders, premenstrual syndrome, irritable bowel syndrome and the prevention of nausea (Source). Much of the research is being conducted with animal rather than human models. A number of medications have been developed that affect how serotonin is taken up by the brain; these are used in the treatment of depression and other mood disorders. Known as SSRIs and SNRIs, these medications include fluoxetine (Prozac), citalopram (Celexa) and sertraline (Zoloft). SSRIs and SNRIs block the brain from reabsorbing serotonin, which increases the levels of the chemical. SSRIs are used in treating panic disorders, anxiety  (try L-Theanine against anxiety) and obsessive-compulsive disorder, as well as depression. Although less commonly used, another class of drugs called MAOI (monoamine oxidase inhibitors), prevent serotonin from breaking down. A typical MAOI drug is isocarboxazid (Marplan). Ondansetron (Zofran) is used in treating nausea, particularly that induced by chemotherapy or anesthesia. “Triptan” drugs such as almotriptan (Axert), Rizatriptan (Maxalt), sumatriptan (Alsuma) and zolmitriptan (Zomig) are used in treating migraines. At one time, drugs that affected serotonin were used for weight loss and treatment of Parkinson’s disease, but these are no longer available. Cocaine and similar recreational drugs inhibit serotonin re-absorption, which is how they create the feeling of being high. Serotonin drugs may have side effects; the most common include gastrointestinal effects, weight changes, neurological symptoms such as dizziness or tremors, sleep changes and headache. In some teens, SSRIs increase the risk of suicide (Source).

How Does Serotonin Affect Our Bodies?

Serotonin plays a major role in the nervous system, the general functioning of the body and the functioning of the gastrointestinal tract. It has also been linked to bone metabolism, lactation – specifically breast milk production – cell division and regeneration of the liver. Some of the systems or functions serotonin is known or thought to affect include:

• Clotting – when you are wounded or cut, the platelets release serotonin. The chemical constricts the tiny arteries called arterioles, reduces the amount of blood flow in the area and promote the formation of blood clots.

• Bone density – osteoporosis is more likely when people have higher than normal levels of serotonin in the bones.

• Bowel function – serotonin in the gastrointestinal tract is important for regulating bowel function and bowel movements. Disruptions in serotonin can lead to either constipation or diarrhea and it seems to play a role in irritable bowel disease. Serotonin is also one of the chemical regulators that influences appetite as you consume a meal.

• Mood – serotonin clearly plays a significant role in mood. Illicit recreational drugs like Ecstasy, for example, cause a dramatic rise in serotonin levels, which is what makes the user feel high. Serotonin is also involved in overall moods, anxiety, depression and feelings of happiness.

• Nausea – serotonin helps protect you from toxins. Should you eat a food or substance that is irritating or toxic, increased levels of serotonin speed up the transit time, helping to expel the irritant though diarrhea. It can also stimulate the center in the brain that causes nausea and vomiting.

• Sexual function – libido and serotonin levels are connected. People who are intoxicated may display increased libido due to lowered serotonin levels. Conversely, people who take medications that increase serotonin levels typically have decreased libido and may also have decreased sexual function, such as an inability to have an orgasm.

Serotonin Syndrome

An excessive amount of serotonin in the body can be very dangerous. Although this condition does not normally exist, it can be induced by taking certain medications (such as two different types of drugs that affect serotonin levels), illegal drugs or dietary supplements. Carcinoid tumors may also cause elevated serotonin levels – they are usually found in the gastrointestinal tract. This potentially life-threatening condition can occur very quickly. Symptoms include agitation, confusion, restlessness, increased blood pressure and heart rate. The patient’s pupils may be dilated and other symptoms such as shivering, nausea, diarrhea, headaches, sweating and muscle rigidity or loss of coordination may also occur. Minor cases can usually be treated by stopping the offending substance, but severe cases may require hospitalization and treatment with medications to manage symptoms or block serotonin production.

How To Boost Serotonin

In addition to medications, scientists think there may be natural ways to boost serotonin levels (they have not all been confirmed by research). These include:

• Mood induction treatment – mood induction is a psychological therapy in which environmental cues such as pictures or music are used to change an individual’s moods. Confirmation of this theory depends on whether there is a two-way relationship between serotonin synthesis and mood.

• Light therapy – full-spectrum light, such as sunlight, is currently used to treat seasonal affective disorder. Studies have indicated that it may also be an effective treatment for depression.

• Exercise – regular aerobic exercise is known to have an effect on mood, probably because of the production of chemicals known as endorphins. A few studies have indicated it may also increase the effect of serotonin in the brain.

• Diet – tryptophan is an amino acid that is required for serotonin production. Foods high in tryptophan, like cheese, chicken, red meat, turkey, nuts and seeds, have been linked to improved moods, possibly because they boost tryptophan levels (Source).

Serotonin is a fascinating chemical that has a significant effect on our bodies’ function and health. From the brain to the gastrointestinal tract to the tiniest arteries in the body, it helps us manage our moods, digest our food and even helps keep us from bleeding. Your lifestyle habits and diets can profoundly affect and be affected by serotonin.

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