Serotonin what does it do

Serotonin

Overview

What is serotonin?

Serotonin, also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter. It also acts as a hormone.

As a neurotransmitter, serotonin carries messages between nerve cells in your brain (your central nervous system) and throughout your body (your peripheral nervous system). These chemical messages tell your body how to work.

Serotonin plays several roles in your body, including influencing learning, memory, happiness as well as regulating body temperature, sleep, sexual behavior and hunger. Lack of enough serotonin is thought to play a role in depression, anxiety, mania and other health conditions.

Most of the serotonin found in your body is in your gut (intestines). About 90% of serotonin is found in the cells lining your gastrointestinal tract. It’s released into your blood circulation and absorbed by platelets. Only about 10% is produced in your brain.

Serotonin is made from the essential amino acid tryptophan. An essential amino acid means it can’t be made by your body. It has to be obtained from the foods you eat.

What does serotonin do in my body?

Serotonin plays a role in many of your body’s functions:

What problems are associated with low serotonin levels?

Low levels of serotonin may be associated with many health conditions including:

Scientists still have a lot to learn about the role of serotonin in the body and in disease.

What can cause low serotonin levels?

A low serotonin level usually has more than one cause. Technically, serotonin levels are low because:

What can I do to increase serotonin levels?

Ways to increase serotonin levels include:

Foods to increase serotonin levels

Many foods naturally contain tryptophan, the amino acid from which serotonin is made. You can try increasing your serotonin level by eating tryptophan-containing foods, such as:

Eating foods high in tryptophan will not necessarily boost serotonin levels on its own. It’s a complex process. Your body needs carbohydrates to release insulin, which is needed to absorb amino acids. Then even if tryptophan does get into your blood it has to compete with other amino acids to get absorbed into your brain. Scientists are still studying how eating tryptophan-containing foods possibly boosts serotonin levels.

Sunlight

Not getting enough exposure to sunlight can lead to the mood disorder seasonal affective disorder in some people. Try to get 10 to 15 minutes of sunlight each day to boost not only serotonin levels but vitamin D levels too. If you live in an area where you can’t get natural sunlight, consider using light therapy to get that needed daily sunlight.

Supplements

Several dietary and herbal supplements also increase serotonin levels. These include:

Exercise

Regular exercise is known to increase serotonin levels. Thirty minutes of aerobic exercise five times a week plus two strength-training sessions per week can improve mood disorders and heart health.

What medications increase serotonin levels?

Serotonin or serotonin receptors are common targets of the pharmaceutical industry since many health conditions are affected by serotonin. Some of the more common medications that increase serotonin levels include the following.

Several different classes of antidepressants block the reabsorption and recycling of serotonin, allowing more to remain in the brain. Medications that work this way are selective serotonin reuptake inhibitors (for example, paroxetine [Paxil®]), serotonin-norepinephrine reuptake inhibitors (for example, venlafaxine [Effexor®]) and tricyclic antidepressants (for example, amitriptyline [Elavil®]). Another type of antidepressant, monoamine oxidase inhibitors (for example, phenelzine [Nardil®]) blocks an enzyme that breaks down serotonin.

Many other medications, taken for many medical conditions, also increase serotonin. Some of these drugs include the triptan family of headache drugs, opioid pain relievers, dextromethorphan-containing cough suppressants and anti-nausea drugs.

What problems are associated with high serotonin levels?

Serotonin syndrome is a condition that happens when serotonin levels are increased too much. It usually happens if you increase the dose of a medication known to increase serotonin levels or take another drug known to increase serotonin.

Mild symptoms include shivering, heavy sweating, confusion, restlessness, high blood pressure, muscle twitches and diarrhea. Severe symptoms include high fever, seizures, fainting and abnormal heartbeat.

Serotonin syndrome can be fatal if it’s severe and not caught early and treated quickly.

Frequently Asked Questions

What’s the difference between dopamine and serotonin?

Dopamine and serotonin are both neurotransmitters. This means they are chemical message carriers between nerve cells in the brain as well as to and from other areas of your body. Both are also considered the “happy hormones,” as they both play a role in positive mood and emotion. Serotonin is associated with happiness, focus and calmness. Dopamine is associated with rewards and motivation. Dopamine and serotonin also share involvement in some mental health conditions, including depression and mood disorders.

Dopamine and serotonin also have some distinct functions. Dopamine controls body movements and coordination. Serotonin helps regulate digestive functions including bowel function and appetite. Dopamine causes a feeling of hunger while serotonin suppresses that feeling. Dopamine is mostly stored in your brain while serotonin is found mostly in your gut.

Sometimes these neurotransmitters work together to stay in a careful chemical balance in your body. Sometimes an imbalance leads to an overproduction of the other neurotransmitter. Having too much or too little of either can cause physical and psychological symptoms.

A note from Cleveland Clinic

Serotonin plays a key role in such bodily functions as mood, sleep, appetite, anxiety, digestion, blood clotting and sexual desire. If you have a health condition that affects serotonin or is affected by serotonin, ask your healthcare provider what you need to know about serotonin. To prevent a swing in your body’s serotonin level and to reduce the potential for drug interactions, don’t stop taking your medications, change your dose or take dietary or herbal supplements without first talking with your provider.

Last reviewed by a Cleveland Clinic medical professional on 03/18/2022.

References

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What Is Serotonin?

A chemical that helps regulate mood

Angelica Bottaro is a writer with expertise in many facets of health including chronic disease, Lyme disease, nutrition as medicine, and supplementation.

Nicholas R. Metrus, MD, is a board-certified neurologist and neuro-oncologist. He currently serves at the Glasser Brain Tumor Center in Summit, New Jersey.

Serotonin is a chemical messenger (neurotransmitter) that helps brain and nervous system cells communicate. Its main function is to stabilize your mood, as well as your feelings of happiness and well-being. Serotonin also plays a role in the digestive system and sleep cycles.

The body needs serotonin, but too much or too little can lead to health issues. For example, too little serotonin can cause depression. Too much, however, can cause a rare condition called serotonin syndrome.

This article discusses the functions of serotonin and what can happen if your levels are off. It also looks at ways to naturally increase your body’s serotonin levels.

What Does Serotonin Do?

Serotonin is produced in the brain. The body uses an amino acid called tryptophan hydroxylase to create it.

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Verywell / Nez Riaz

Serotonin plays a key role in the central nervous system, which is composed of the brain and spinal cord). This system controls the majority of your body and mind functions.

Serotonin is responsible for mood regulation. It can reduce feelings of depression and anxiety and increase feelings of joy or happiness. It also plays a role in other aspects of your health, including:

Having too much or too little serotonin can cause problems with these functions.

Serotonin Deficiency

It is possible for your serotonin levels to be too low. Serotonin deficiency can be caused by:

How Low Levels Affect the Body

Serotonin affects many body processes. For this reason, inadequate amounts can lead to both psychological and physiological issues. Some symptoms and conditions associated with serotonin deficiency can be grouped into these categories:

Low serotonin levels have also been associated with certain chronic diseases. This includes Alzheimer’s disease and Parkinson’s disease.

When Serotonin Is Too High

Most of the time, dangerously high serotonin is caused by drugs that increase serotonin activity. In rare cases, it’s can be caused by a tumor.

Excessive serotonin levels can be life-threatening.

Serotonin Syndrome

Serotonin syndrome occurs when serotonin levels in the body become too high. It can be life-threatening and requires emergency medical care.

Serotonin syndrome doesn’t usually occur naturally. Common causes of serotonin syndrome include:

Symptoms of serotonin syndrome can be mild or severe. Mild symptoms may include:

Moderate symptoms can include:

In severe cases, serotonin syndrome can cause:

Without immediate treatment, serotonin syndrome can lead to unconsciousness and death.

If you have any of the above symptoms and have recently started or increased your dose of a medication that can affect serotonin levels, seek medical care right away.

Carcinoid Syndrome

A condition called carcinoid syndrome can cause high serotonin levels in the blood. This syndrome is caused by a tumor that produces too much serotonin. Symptoms can include:

Regulating Serotonin

It is possible to boost low serotonin with supplements or lifestyle changes like diet and exercise. High serotonin, however, requires immediate medical treatment.

Treating Low Serotonin

Medications can help treat low serotonin. These include SSRIs, which help the body make better use of serotonin. These drugs are often prescribed if you have symptoms of depression. Depending on the length and severity of your symptoms, you may need to take SSRIs long term.

Certain dietary supplements can also help restore normal serotonin levels, including:

It is important to remember that some supplements, especially when combined with drugs that affect serotonin levels, may put you at risk for developing serotonin syndrome. Always ask a healthcare provider before starting a new supplement.

There are also natural ways to boost your serotonin levels. You may need to do these things regularly in order to keep your serotonin levels high:

Treating High Serotonin

People with serotonin syndrome are typically hospitalized for a minimum of 24 hours.

Mild cases caused by medication can usually be resolved by stopping the medication or changing the dose.

Healthcare providers may also prescribe medications that can stop the body from producing serotonin, help relieve symptoms, and keep the condition from worsening. Medications that may be used in the hospital include:

Longer hospital stays may be required in severe cases, in which patients need close monitoring for changing or worsening symptoms.

Patients may need medications that paralyze their muscles. Some may also need to be temporarily put on a breathing machine to prevent muscle damage.

Summary

Serotonin is a neurotransmitter. It plays an important role in regulating mood, sleep, and your digestive system.

High or low levels of serotonin can lead to health problems. High levels of serotonin can cause serotonin syndrome, a life-threatening condition. Low levels can cause depression. Both high and low serotonin can be treated with medication. There are also natural ways to boost low serotonin levels.

Frequently Asked Questions

The prevalence of serotonin syndrome isn’t known. One small study found that roughly 7.8% of 309 intensive care unit (ICU) patients had some symptoms of serotonin syndrome. It’s important to note, though, that this is not a typical patient population.

The release of serotonin can happen at different times of the day during different activities. It is also produced when you eat something that makes you nauseous. Massage therapy, spending time in sunlight, and exercising have also been shown to trigger the release of serotonin.

There is no set time for how long it takes to replenish serotonin. This is because brain chemistry varies from person to person. For mild cases of serotonin deficiency, levels may be replenished quickly. In other cases, it may take longer.

What Is Serotonin?

The purpose of serotonin, ways to increase it, and how much is too much

Daniel B. Block, MD, is an award-winning, board-certified psychiatrist who operates a private practice in Pennsylvania.

What Is Serotonin?

Serotonin (also known as 5-hydroxytryptamine or 5-HT) is a naturally occurring substance that functions as a neurotransmitter to carry signals between nerve cells (called neurons) throughout your body. Most commonly, people are aware of serotonin’s role in the central nervous system (CNS).

In the brain, serotonin helps with mood regulation and memory, but it also has important jobs in other parts of the body. In fact, most of the serotonin in your body is found in your gut, not your brain. The intestines produce almost all of the body’s serotonin supply, and serotonin is required to promote healthy digestion.

Elsewhere in the body, serotonin helps with sleep, sexual function, bone health, and blood clotting. Here’s a closer look at serotonin’s many functions, what happens if you have too little (or too much), and a few ways to balance your levels for optimum health.

What Serotonin Does

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Verywell / Nez Riaz

Serotonin is known to be involved in many bodily functions, ranging from regulating mood to digesting food.

Serotonin’s effects on the brain could be considered its starring role in the body. As it helps regulate mood, serotonin is often called the body’s natural «feel-good» chemical. Serotonin’s influence on mood makes it one of several brain chemicals that are integral to your overall sense of well-being.

Serotonin’s effect on mood is also why it’s often a target of medications that are used to treat depression, anxiety, and other mood disorders. For example, increasing serotonin levels is the purpose of the class of antidepressants known as selective serotonin reuptake inhibitors (SSRIs).

Digestion

Serotonin contributes to normal bowel function and reduces your appetite as you eat to help you know when you’re full. It also plays a protective role in the gut.

For example, if you eat something irritating or toxic, your gut responds by producing more serotonin. The extra dose moves the unwanted food along, expelling it from your body more quickly.

The response is also why increased levels of serotonin can make you nauseated, and why drugs that target specific serotonin receptors can be used to alleviate nausea and vomiting.

Sleep

The exact nature of serotonin’s role in sleep is still being studied, but it’s believed to influence when, how much, and how well you sleep. Serotonin does not regulate these tasks alone; other neurotransmitters like dopamine also play a key role.

A hormone called melatonin is also critical to the proper functioning of the sleep cycle. Your body needs serotonin to make melatonin, so not having enough serotonin (or having too much of it) can affect the pattern and quality of your sleep.

The serotonin-melatonin relationship might also contribute to sleep disruptions like insomnia, which are common in people with depression.

Your brain has specific areas that control when you fall asleep, regulate your sleep patterns, and wake you up. The parts of your brain that are responsible for regulating sleep also have serotonin receptors.

In the case of serotonin vs. dopamine, for instance, serotonin can either help you fall asleep or keep you from sleeping, depending on where it is released in the brain. Dopamine will keep you awake.

Blood Clotting

When you have any kind of tissue damage, such as a cut, the platelet cells in your blood release serotonin to help heal the wound. Increased serotonin levels cause the tiny arteries (known as arterioles) of the circulatory system to narrow. As they get smaller, blood flow slows.

This narrowing (known as vasoconstriction) and slowed blood flow are two important elements of blood clotting—a crucial step in the process of wound healing.

Bone Density

Studies have shown that serotonin levels may influence bone density (the strength of your bones). Research suggests that high circulating levels of serotonin in the gut might be associated with lower bone density and conditions like osteoporosis.

Research suggests that SSRI medications are associated with decreased bone mineral density. Low bone density puts you at a greater risk for fractures.

If you are concerned about how taking an antidepressant could affect your bone density, do not stop taking your medication. Start by talking to your healthcare provider about other risk factors, such as having a family history of osteoporosis or smoking.

Sexual Function

In addition to altering mood, serotonin can also influence the frequency and intensity of sexual feelings.

Certain antidepressants that increase serotonin levels can have an effect on libido, as elevated serotonin levels have been associated with a decrease in sexual desire.

Serotonin’s influence on libido is also somewhat related to its relationship to dopamine. For example, a 2017 study of women with hypoactive sexual desire disorder (HSDD) found that symptoms of the condition were associated with increased serotonin activity and reduced dopamine activity.

Causes of Low Serotonin

Depression and other mood disorders that are linked to serotonin are multifactorial, meaning there is more than one reason they occur. Having low serotonin levels is not, on its own, enough to cause depression. Low levels can, however, contribute to mood, sleep, and digestive problems, and other issues.

There’s no single cause of low serotonin levels, but it typically occurs for one of two reasons: not having enough serotonin or inefficient use of the serotonin you have. In the first scenario, you have low levels of serotonin because your body is not producing enough to maintain normal levels.

Your body might not be able to produce enough serotonin because of other factors, such as nutritional and vitamin deficiencies.

For example, low levels of vitamin B6 and vitamin D have both been linked to decreased levels of serotonin. Tryptophan, an essential amino acid involved in serotonin production, can only be obtained through diet.

The other reason you might have a serotonin deficiency is that while your body is making serotonin, it is not using it effectively. This can happen if you don’t have enough serotonin receptors in your brain, or if the ones you have don’t work well (for example, they absorb and break down serotonin too quickly).

Signs of Low Serotonin

How do you know if your serotonin levels may be low? Signs of a potential serotonin deficiency include:

Studies also suggest that serotonin levels may decrease with age, potentially due to a decline in the function of serotonin receptors and transporters.

How to Increase Serotonin

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Verywell / Madelyn Goodnight

Depression is known to be associated with chemical imbalances in the brain. While serotonin’s role in depression is more complex than an imbalance, it is believed to play a key role.

Increasing how much serotonin is in the brain appears to improve communication between brain cells, which in turn lifts mood and reduces symptoms of depression. This is why prescription antidepressant medications are used to treat clinical depression and other mood disorders.

There are also natural ways to increase serotonin levels. Everything from the food you eat to how much sunlight you get can affect how much serotonin your body has, as well as how effectively it can use it—both of which can help correct a serotonin deficiency.

Selective Serotonin Reuptake Inhibitors (SSRIs)

SSRIs are the most commonly prescribed antidepressants worldwide. These drugs are used to reduce the symptoms of moderate to severe depression by increasing the amount of serotonin in the brain.

When brain cells send signals to one another, they release neurotransmitters, including serotonin. Before they can send the next signal, the cells must reabsorb and recycle the neurotransmitters they have released. This process is called reuptake.

SSRIs make more serotonin available in the brain by blocking the serotonin reuptake process.

Examples of SSRIs that are commonly prescribed to treat depression and other mood disorders include:

Medications such as Viibryd (vilazodone) are not only an SSRI but also a 5HT-1a partial agonist. Drugs in this class are not solely classified as SSRIs, but rather, as serotonergic antidepressants. Trintellix (vortioxetine) is a similar drug.

Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)

Another group of serotonin-based medications for treating depression is known as serotonin-norepinephrine reuptake inhibitors (SNRIs). These drugs work similarly to SSRIs in that they block the reuptake of serotonin, but they also work on norepinephrine, another neurotransmitter that affects mood.

Drugs that act on both serotonin and norepinephrine are sometimes referred to as “dual-acting antidepressants.”

Popular SNRIs include:

Tricyclics (TCAs) and Monoamine Oxidase Inhibitors (MAOIs)

Two older classes of antidepressants also affect serotonin levels: tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs).

TCAs appear to block the reabsorption of serotonin and norepinephrine, which effectively increases the amounts available in the brain.

Examples of TCAs include:

MAOIs block the effects of the monoamine oxidase enzyme, which breaks down serotonin, epinephrine, and dopamine. Preventing these neurotransmitters from being broken down effectively increases the amounts available in the brain.

Examples of MAOIs include:

TCAs and MAOIs are not prescribed as often as other antidepressants because they tend to have more side effects than SSRIs and SNRIs. 

Many foods naturally contain serotonin, but your body also needs other nutrients, such as tryptophan, vitamin B6, vitamin D, and omega-3 fatty acids, to produce serotonin.

Foods that are good sources of these key nutrients include:

Eating a high-fiber diet that is rich in fruits and vegetables will help keep your gut bacteria healthy. Having a good balance of friendly bacteria in your intestines has been linked to adequate serotonin levels (as the intestines make about 95% of your body’s supply).

Exercise

Regular physical activity (especially aerobic exercise) has been proven to boost serotonin levels. However, the benefits of regular exercise go beyond your brain.

Exercise can help people manage depression and other mood disorders by also promoting cardiovascular health, improving strength and endurance, and helping to maintain a healthy weight.

The Department of Health and Human Services recommends that adults get at least 150 minutes of moderate-intensity cardio exercise each week plus strength training two days per week.

Talk to your healthcare provider before starting an exercise routine. Be sure to pick activities that you enjoy, as you’ll be more apt to stick with them, and consistency is key to getting all the benefits.

Light Exposure

Your levels of serotonin might get low if you don’t get out in the sun regularly. Not getting enough exposure to sunlight is one theory behind why people experience depression during the short, dark days of fall and winter (a mood disorder called seasonal affective disorder).

Try to spend 10 to 15 minutes outside in the sun each day. Sunlight also boosts your levels of vitamin D, which is needed for serotonin production.

If you live in a place with little to no sunlight, you can also use light therapy to make sure you’re getting your daily dose of sunshine.

Massage

Massage therapy has been found to promote the release of serotonin and decrease the stress hormone cortisol, making it an appealing non-pharmaceutical addition to depression and anxiety treatment plans. You don’t even need a professional massage to reap the benefits.

A frequently cited study of pregnant women with depression published in the International Journal of Neuroscience in 2004 concluded that massage could be beneficial even when given by someone who isn’t a trained massage therapist.

After participants in the study had two 20-minute massage sessions given by their partners, their serotonin levels increased by 28% and their dopamine levels by 31%.

Supplements

While you can improve your overall nutrition through your diet, certain supplements may also be helpful. Popular dietary supplements you might want to consider include:

Dangers of Too Much Serotonin

Always ask your healthcare provider before taking any medication or supplement to increase low serotonin. Certain medications and supplements can raise serotonin levels too much, which can lead to serotonin syndrome.

Serotonin syndrome is a condition resulting from elevated serotonin levels, It often occurs when someone is first taking a new drug that affects serotonin, or if the dosage of a current drug is increased.

The symptoms of serotonin syndrome range from unpleasant to life-threatening and can include sudden swings in blood pressure, seizures, and loss of consciousness. Too much serotonin can also cause an increase in anxiety or nervousness.

Serious cases of serotonin syndrome can be fatal if left untreated. If you or a loved one is showing symptoms of serotonin syndrome, call 911 or go to the nearest emergency room.

A Word From Verywell

When your body doesn’t have enough serotonin, or if it isn’t using the serotonin you have effectively, you might be more prone to symptoms of depression and other mood disorders. And while low levels of serotonin can cause problems, having too much serotonin can also be an issue.

If you’re concerned about the symptoms you’re experiencing, talk to your healthcare provider. If your serotonin levels are a culprit, you are not alone and there are many treatment options available, including both medications and lifestyle changes.

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Carhart-Harris R, Nutt D. Serotonin and brain function: A tale of two receptors. J Psychopharmacol. 2017;31(9):1091-1120. doi:10.1177/0269881117725915

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What Is Serotonin and What Does It Do

At a Glance

In general terms, serotonin is often most closely associated with mood, and in particular with depression. In reality, however, it has many different functions.

Due to the complexity of our bodies, especially the brain, and the difficulty of isolating the specific influence of a single chemical, we still do not fully understand the role of serotonin in the body in respect of all of its functions.

However, research that has been conducted to date can identify and explain some, but not all of its functions. In this article we’ll take a look at the questions: “what is serotonin and what does it do?”

What Is Serotonin?

Serotonin is a chemical which is produced by cells in the nervous system. It is made from an amino acid, the building blocks of protein, called tryptophan.

Tryptophan is one of nine essential amino acids, so called because the body is unable to manufacture it – tryptophan has to be sourced through our diet, in foods such as milk, cheese, nuts, red meat and chickpeas. (source)

Serotonin cannot be transported into or out of the brain, and since it is found in the body in the brain, the digestive system and in blood platelets, scientists have concluded that the serotonin used in the brain must be produced in the brain, and the serotonin that acts on systems outside of the central nervous system is produced at other sites.

In both cases, serotonin is produced from tryptophan, which undergoes several stages of chemical changes to produce serotonin. The chemical name for serotonin is 5-hydroxytryptamine, or 5-HT.

The serotonin is then attached to specialized molecules which transport it. As much as 90 percent of our serotonin is found in the digestive tract and the blood platelets, but is also found in the central nervous system, where it has to bind with serotonin receptor cells to become active.

Some research has identified serotonin receptors in specific parts of the brain. These include the cortex, which is responsible for personality traits, conscious thoughts and actions, the amygdala, responsible for emotions, survival instincts and memory, and the hippocampus, associated with memory and spatial awareness. (source)

Other studies, however, indicate a more widespread use of serotonin throughout the central nervous system stating that most structures within the central nervous system show evidence that serotonin plays a role in many of their functions. (source)

What Does Serotonin Do?

The main function of serotonin is to transmit messages between different nerve cells. Although that sounds fairly simple, when we consider that our nervous system in turn controls all the functions in the body, we start to see that serotonin can affect a wide number of body functions.

Add to this the complexity of the brain and nervous system, and the fact that scientists do not fully understand many of the functions of the brain. We then start to appreciate why research cannot fully explain all of the functions of serotonin.

However, there is some clear evidence that demonstrates the role of serotonin in some cases. Let’s take a look.

Regulates Mood

Serotonin is thought to be responsible, at least in part, for regulating our feelings of happiness or sadness, anxiety and overall mood. Drugs which are known to drastically change our mood, like LSD and ecstasy have been shown to dramatically increase the levels of serotonin in the body. (source)

Research has linked low levels of serotonin with a lowered mood state, but notes that this does not usually happen independently. Scientists believe that there must be some kind of interaction between serotonin and other chemicals in the body which results in low mood, although they are currently unable to identify any specific interactions. (source)

Serotonin and Depression

Depression is an illness which has many potential causal factors. This makes it difficult to identify the precise effect of serotonin on depression.

Research studies have most certainly identified a link between serotonin and depression, but the exact nature of the relationship is unclear. It is difficult to determine whether depression causes decreased levels of serotonin in the body or decreased amounts of serotonin are a factor in the onset of depression.

There is, however, a whole group of medications called selective serotonin reuptake inhibitors (SSRIs) which work by preventing or minimizing the reabsorption of serotonin from the bloodstream which are commonly used to treat anxiety, depression and obsessive-compulsive disorders, and have been shown to be clinically effective, but scientists are unable to categorically state exactly how they affect depression. (source)

In recent years, one study in mice compared one group of subjects with low serotonin levels with another group with normal levels of serotonin in a series of behavioral tests designed to evaluate the subjects for depression.

They found no signs of depression in either group, and concluded that a low level of serotonin is not a factor in the development of depression. However, much more research is needed using human subjects, before this information can be stated as fact. (source)

Serotonin and Muscle Function

Serotonin is thought to have a significant role in constricting smooth muscles, such as in the digestive system, in the cardiac muscle of the heart and other internal organs which are not under voluntary control.

More recent research indicates that serotonin can be found in skeletal muscle fibers. It has been shown to help promote muscle growth, and further research is being conducted in this area. (source)

The Role of Serotonin in Digestive Disorders

Since such a large percentage of the body’s serotonin is found in the digestive system, it is unsurprising that it also has significant effects within this region.

Most of the serotonin in the digestive system is thought to play a key role in regulating the body’s bowel movement and function. As well as playing its part in normal bowel function, serotonin also has an important protective role in the gut.

The body produces increased levels of serotonin in response to the detection of a toxic substance in the digestive tract, which speeds up the digestive process to decrease the amount of the substance that is absorbed into the bloodstream, and to expel the substance as diarrhea. (source)

Research indicates that low levels of serotonin are associated with constipation, while high serotonin levels have been observed in diarrhea and celiac disease.

Serotonin also appears to play a role in irritable bowel syndrome (IBS), a condition which can present with symptoms of either constipation or diarrhea.

Some research suggests that abnormal levels of serotonin after consuming food may be related to the symptoms of IBS, with IBS patients presenting with constipation having low levels of serotonin, and IBS patients who present with diarrhea having high levels of serotonin. (source)

Controls Sleep

There is still much about our sleep patterns that are not fully understood. However, according to research from Harvard Medical School, the hypothalamus is the main center of the brain responsible for driving our sleep response. (source)

Historically, scientists thought that serotonin was only responsible for initiating and maintaining sleep. However, more recent research has shown that serotonin can also inhibit sleep, depending on how it is used in the brain. (source)

Serotonin and Pain

Recent research has investigated the relationship between serotonin and pain threshold – the amount of pain our bodies are able to cope with before we experience the sensation of pain.

One clinical trial reported that limiting the available tryptophan, and therefore decreasing the amount of serotonin in the body resulted in a significant increase in sensitivity to pain. (source)

However, not all research on the subject of pain agrees, especially with reference to specific pain-inducing health conditions.

For example, some studies have found that low levels of serotonin have been associated with conditions such as fibromyalgia (source), whereas high levels of serotonin has been correlated with chronic regional pain syndrome, commonly known as CRPS. (source)

While this evidence seems to be contradictory, the one thing these two conditions have in common is that neither of them are fully understood by medical science.

Pain is Complicated

Pain is an incredibly complex issue that some experts devote their careers to in an effort to discover more about pain. One of the reasons why pain is so complicated is that it’s a phenomenon that involves many pathways, and the amount of pain we experience depends on our circumstances.

Anxiety, for example, plays a significant role in our pain perception. To illustrate this, consider shutting your hand in your car door.

Painful? Of course it is.

But the brain moderates our response to the pain according to our mood and situation. If we were on our way to the dentist for a root canal and we’re panicking about it, the pain is likely to be much more intense than if we were just on our way to collect our prize from a winning lottery ticket. This data is well supported in research. (source)

What we can say is that although the relationship between pain and serotonin might be complicated and far from fully understood, there seems to be a definite link; some medications which act to keep as much serotonin and norepinephrine, a hormone and neurotransmitter, as active as possible in the body have been proven to reduce chronic pain in some conditions. (source)

Serotonin and Bone Health

Serotonin has been closely linked with bone health, although studies have produced conflicting results.

Some studies have shown that high levels of serotonin in blood serum are associated with low bone mineral density. They suggest that over a long term this can lead to osteoporosis – a condition where the honeycomb structure of the bones is broken down, resulting in weak brittle bones which are more prone to fractures when exposed to excessive forces. (source)

Other studies, however, indicate that long term high levels of serotonin, a condition called hyperserotonemia, results in increased bone mass density in non-human subjects. (source)

Further research has attempted to explain the conflicting results, and has identified that a microsystem involving serotonin exists within bones. Some research suggests that serotonin increases the production of osteoclasts – bone cells responsible for bone reabsorption, but it can also stimulate the production of osteoblasts – the cells that build and reshape bones. However, there is a need for further research in this area. (source)

Helps Heal Wounds

Serotonin is released from platelets in the blood, and has the effect of constricting the tiny blood vessels – arterioles and capillaries – near the surface of the skin when we suffer a wound. This reduces the flow of blood and makes it easier for the platelets to form a blood clot to seal the wound ready for repair. (source)

Regulates Sexual Function

Studies indicate that when serotonin levels are low, libido increases, and conversely, high levels of serotonin is associated with a reduced sexual drive. This is particularly evident in patients on SSRI medication; with some studies indicating the occurrence of sexual dysfunction as being between 30 and 60 percent. (source)

Stimulates Nausea

Scientists have identified a clear link between serotonin and nausea. In response to toxic substances, or something that irritates the digestive system, serotonin stimulates particular nerve fibers that trigger nausea and cause us to vomit in an attempt to expel the undesirable substance.

Many antiemetic drugs intended to reduce or prevent nausea and vomiting act by blocking serotonin receptors, and so decrease the level of serotonin which is active in the body. (source)

Serotonin Syndrome

This is a medical condition which results from over-stimulation of the central nervous system, including serotonin receptors. It can occur through taking medication, supplements or illegal drugs, or a combination of these which leads to serotonin levels becoming too high.

For this reason, all medications that result in increased levels of serotonin carry a warning not to mix them with any other type of medication or substance that have a similar effect – for example, migraine medication and St John’s Wort – a common supplement which is taken to help manage depression and anxiety.

Similarly, some types of tumors cause increases in serotonin, and in these cases it is not appropriate for people to take medication like SSRIs or St John’s Wort.

Serotonin syndrome results in dramatically increased activity within the nervous system, and can lead to seizures and loss of consciousness. It can potentially be life threatening. The symptoms of serotonin syndrome become apparent after several hours of ingesting the substance and include:

If serotonin syndrome is suspected, immediate medical attention is necessary. It can be easily diagnosed, and while less severe cases may simply require the patient to stop taking the combination of medication which caused serotonin syndrome, more severe cases may need hospital treatment to monitor and restore serotonin levels to normal.

Natural Serotonin Boosters

There are several ways in which we can naturally increase low levels of serotonin.

Considering that we need the amino acid tryptophan from our diet, it makes sense that if we increase the amount of foods high in tryptophan in our diet, we can also increase our levels of serotonin.

However, when it comes to the brain – as usual – it’s not that straightforward.

For tryptophan in the diet to be used to produce serotonin in the brain, it relies on particular transporter molecules. These transporter molecules are able to carry several different types of amino acids.

This creates a high level of competition between the various types of amino acids for the transporter molecules, and the other types of amino acids are generally found in more abundant amounts than tryptophan.

As a result, far less tryptophan gets transported to the brain compared to other amino acids. Essentially, this means we need to consume foods that are higher in tryptophan than in other types amino acids in order to promote increases of serotonin levels in the brain. (source)

Light Therapy

A treatment which has become a popular and recognized way to manage conditions such as seasonal affective disorder (SAD), a disorder which results in low mood and depressive symptoms during the winter months in people who do not experience any symptoms throughout the rest of the year.

Light therapy involves being exposed to an artificial light source that mimics natural light. It is thought to work by affecting various chemicals in the brain linked to mood.

Research indicates that it is a useful treatment for depression, with some studies suggesting that light therapy can be as effective as antidepressant medication. (source)

Exercise

Research has long shown that exercise has a significant positive effect on mood, and some studies indicate it can increase the levels of serotonin in the brain.

Clinical research has proven that exercise results in a significant increase in the release and synthesis of serotonin, and levels of tryptophan in the brain following exercise. (source)

The best effect of exercise in improving mood has been observed in research when people take part in regular, consistent exercise with which they are familiar.

It appears that trying new forms of exercise which require skills that are new to the participant and need to be developed with regular practice can create higher levels of anxiety which can be unhelpful in using exercise to improve depressive symptoms. (source)

In Summary

Serotonin is a chemical produced by the body from a specific amino acid, tryptophan. While serotonin has traditionally been associated with brain function, and does play a key role in regulating mood and depression, it is found primarily in the digestive system, blood platelets and in bone.

Serotonin has a significant role in the function of all muscle tissue, and has been identified as important in regulating bowel function and protecting the digestive system from toxins and irritants, causing vomiting and diarrhea to expel irritants if necessary.

Serotonin is also thought to help control sleep, and has been shown to be able to initiate, maintain and inhibit sleep, depending on how it is used by the body.

Serotonin has been shown to have a significant effect on increasing pain threshold and mediating the body’s response to pain.

While serotonin has been shown to decrease one density in some studies, other research indicates high levels of serotonin are linked with increased bone density. Too much serotonin active in the body can result in serotonin syndrome, which can require immediate medical attention.

Research studies generally agree that serotonin plays an important role in blood clotting and wound healing, and that it inhibits sexual function.

It is possible to increase low levels of serotonin in several ways, including the use of medication, light therapy, exercise and diet, although diet is not the method of choice when the goal is to increase the levels of serotonin in the brain.

While not all research is in agreement about serotonin, what is abundantly clear is that serotonin plays an extremely important role in a wide variety of human body functions, and has a significant effect on many different systems within the body.

As brain function and the impact of hormones and other chemicals is yet to be fully understood, it is unsurprising that in many cases, the role of serotonin is also not fully understood.

Serotonin Definition, Function & Effects of High/Low Levels

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Serotonin is both a hormone and neurotransmitter. It is essential for regulating mood, movement, sleep & much more. What else does it do, and what happens when it’s out of balance? Read on to find out more!

What is Serotonin?

Definition & Overview

Serotonin is an important signaling molecule throughout the brain and body. It is commonly known as the “happiness neurotransmitter” or the “happiness hormone” due to its prominent role in regulating mood.

Serotonin plays an important rol,e in the brain, where its main job is to transmit messages between nerve cells. According to some scientific theories, serotonin is involved in all aspects of human behavior [1, 2].

However, brain serotonin makes up less than 2% of the total serotonin found in our bodies. Most serotonin (over 90%) is actually made, stored, and released by the gut. In addition, about 5-8% of serotonin is stored in platelets circulating in the blood [1, 3, 4].

As such, the roles of serotonin in the body are many and diverse. Research suggests that serotonin influences [4, 1, 3, 5, 2]:

What Does Serotonin Do?

Originally discovered in the 1940s, serotonin — also known as 5-hydroxytryptamine, or “5-HT” for short — is currently believed to play many pivotal roles in mood, behavior, gut, and overall optimal body function (homeostasis). So-called “imbalances” or other abnormalities in serotonin function have been linked with symptoms that may interfere with mental and physical health, and which can significantly impair quality of life [6, 7, 8].

According to some hypotheses and limited research, increasing serotonin levels may help with anxiety, depression, migraines, and constipation-predominant irritable bowel syndrome. However, more large-scale studies are needed [6, 7, 8].

Production and Removal

The majority of serotonin is made, stored, and released by cells in the gut lining (enterochromaffin cells). These cells make serotonin from the amino acid L-tryptophan, which is the main “building block”, or metabolic precursor of serotonin [9, 10].

Certain specific types of bacteria in the human digestive tract are believed to boost serotonin production in the gut. Gut flora actually balances tryptophan metabolism (via the kynurenine pathway), influencing the amount of L-tryptophan available for making serotonin [11, 12].

However, serotonin produced by the gut cannot cross the blood-brain barrier. That is why brain cells must produce their own serotonin, either from L-tryptophan or 5-hydroxytryptophan (5-HTP), a byproduct of L-tryptophan [13, 14].

Conversely, excess serotonin and the brain and gut is “deactivated” by several different mechanisms. For example, proteins called serotonin transporters effectively “clean up” or “remove” (re-uptake) serotonin from neural synapses, and bring them back into neurons where it can be reused [15, 9].

Alternatively, serotonin that is released into the bloodstream either gets taken up (absorbed) by platelets, or is broken down (metabolized) in the liver and lungs by enzymes called monoamine oxidase (MAO-A), aldehyde, and alcohol dehydrogenase [3].

Other Neurotransmitters

Monoamines

Serotonin is just one member of the “monoamine” family of neurotransmitters, which also includes other major neurotransmitters such as norepinephrine and dopamine. Researchers currently believe that all of these neurotransmitters work together to influence and regulate mood [16].

By extension, a person’s levels of each of these neurotransmitters may affect their mood. For example, a meta-analysis of data from more than 50 different studies reported that artificially depleting the levels of these neurotransmitters can cause “low mood” and other related symptoms (this is typically done by depleting the body of the metabolic precursors needed to make these neurotransmitters, such as tryptophan or tyrosine). However, these effects were only observed in individuals who had certain pre-existing risk factors — such a prior diagnosis of depression, or a family history of depression disorders — and are not necessarily seen in otherwise healthy people [16].

Imbalances in the levels or relative activity of serotonin, dopamine, and norepinephrine have also been proposed to play a role in other common psychiatric conditions, such as bipolar disorder [17].

However, some researchers have proposed that combined low levels of these three neurotransmitters — and not just low serotonin alone — may be important for understanding how these mood disorders originally develop and progress [17].

Hormones

In the pineal gland, serotonin is used to make melatonin, a hormone that synchronizes the body’s “biological clock” or circadian rhythm. When serotonin is low, that limits the amount of melatonin that can be made in the body, potentially interfering with the sleep-wake cycle [5].

Download the Stress Less guide to discover natural supplement and lifestyle recommendations designed to help you beat stress and improve your mood.

Associated Health Conditions & Disorders

Note that when we talk about serotonin-associated disorders, it’s important to realize that these disorders are not necessarily directly due to serotonin levels or production per se. Rather, they may instead stem from issues with serotonin reuptake, or the availability of certain serotonin receptors. There are over 15 different receptor types discovered to date, including the well-known 5-HT1A, 5-HT2A, and 5-HT2C [18, 19, 20].

Additionally, the majority of studies covered in this article deal with associations only, which means that a direct cause-and-effect relationship hasn’t yet been conclusively established.

For example, just because depression has been associated with low serotonin in certain brain areas doesn’t mean that depression is actually directly caused by low serotonin. Data are lacking to make such claims.

Also, even if a study did find that low brain serotonin contributes to depression, serotonin levels are highly unlikely to be the only causative factor. Complex disorders like depression always involve multiple possible factors — including brain chemistry, environment, health status, and genetics — which may vary from one person to another, and which may interact in highly complex ways to cause any particular effect on health or well-being.

With this in mind, limited studies have linked abnormal serotonin levels with [2, 4, 1, 21, 22]:

Additionally, scientists believe serotonin connects the gut microbiome with the brain – forming the so-called “gut-brain axis.” Decreased diversity and stability of beneficial gut bacteria has been linked with serotonin-related health issues — especially in the elderly [23, 24, 25].

When To “Increase” Serotonin Levels?

Like any bioactive substance in the body and brain, serotonin levels need to be carefully balanced in order to ensure optimal overall health.

However, this important fact sometimes gets lost in the way that many people discuss certain popular health topics, such as serotonin and dopamine levels. Unfortunately, it’s often possible to come away with the impression that having “more” of these is always “better” — which is definitely not the case!

For example, elevated levels of serotonin can cause serotonin syndrome — a serious medical condition that can be potentially fatal [26, 27, 28].

Additionally, increasing serotonin levels can sometimes worsen the symptoms of other pre-existing conditions (such as OCD) [29, 30, 31].

Therefore, it shouldn’t be assumed that increasing serotonin levels or activity is necessarily always a good thing. For this reason, it is crucially important to always talk to your doctor first before deciding to try any lifestyle changes or new supplements, as only a qualified medical professional can help you determine the most effective and safest course of treatment for you, based on your specific health needs and medical history.

Testing Serotonin

Serotonin that gets released into the blood gets rapidly broken down in the liver and lungs, to inactive metabolites (such as 5-HIAA) that are eventually excreted in urine [3].

This is why blood and urine typically contain trace amounts of serotonin. By extension, a person’s level of serotonin in these bodily fluids can sometimes be a useful diagnostic marker for serotonin-related abnormalities and health conditions. For example, larger quantities of serotonin in the blood/urine can be observed in people with serotonin-producing tumors (carcinoid tumors).

Nonetheless, there are a wide range of important limitations that reduce the reliability of urine tests when trying to “estimate” the actual levels of serotonin available in the brain. For example [32]:

For these reasons, it is useful to remain skeptical about the use of urine serotonin levels to check for so-called “neurotransmitter imbalances.” While many companies that provide these tests state that the levels in urine directly and reliably correspond to brain neurotransmitter levels, research has repeatedly shown that this is not necessarily the case [32].

In addition, many of these companies have also been known to intentionally use extremely narrow reference ranges, without any scientific support whatsoever — often in order to sell supplements to their clients [33]!

By contrast, more reliable tests of serotonin levels include cerebrospinal fluid (CSF) tests, or measurements of serotonin in blood platelets. This is because these measurements are either more “direct” measurements of serotonin in brain and nervous system (such as for CSF tests), or are based on measurements that are more “stable,” and have less sudden fluctuations over time (such as for platelet tests) [34, 35].

Ultimately, however, getting a PET scan is really the only “direct” way to accurately and reliably detect changes of serotonin production in specific areas of the brain [35].

Risks and Safety

Like any bioactive compound, serotonin (and the substances that potentially influence it) have the possibility of causing adverse side-effects and other potential risks and dangers.

Additionally, any substance or other factor that can influence serotonin levels also has the potential to have unpredictable and negative interaction with other dietary factors, supplements and medications, pre-existing health conditions, and other important health-related factors.

Therefore, always make sure to discuss any new supplements or lifestyle changes with your doctor first. Also make sure that he- or she is fully aware of any other relevant factors (such as special diets, current medications, or supplements) that may impact your health. The information in this post should never be used to replace conventional treatment.

Serotonin Syndrome

Excess serotonin may result in serotonin syndrome, which often results from adverse drug interactions, and which can be fatal [36].

MDMA, LSD, and other synthetic drugs may cause serotonin syndrome, and should not be taken without medical supervision or outside a psychotherapeutic environment [37].

>>> To learn more about serotonin syndrome, you can check out our detailed and comprehensive post on it here.

Drug Interactions

The use of St. John’s Wort, SAM-e, or lithium simultaneously with serotonergic drugs such as selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), or triptans can greatly increase the risk of serotonin syndrome, a life-threatening and potentially fatal condition [26, 27, 28].

Other Potential Risks

Abnormally heightened blood levels of serotonin (hyperserotonemia) is a consistent finding in individuals with autism. Relatedly, pregnant women with hyperserotonemia have been reported to be more likely to give birth to children with autism [38, 39].

Takeaway

Serotonin is an important signaling molecule throughout the brain and body. It is commonly known as the “happiness neurotransmitter” or the “happiness hormone” due to its prominent role in regulating mood.

The majority of the serotonin in the human body is made and metabolized entirely in the gut. The brain must produce its own serotonin, as this hormone cannot cross the blood-brain barrier.

Serotonin has a vast array of known and suspected functions, including in regulating mood (a task it appears to share with other neurotransmitters like dopamine), movement, sleep, body temperature, appetite, gut function, blood clotting, immune response, and much more.

Imbalances in the serotonin system have been associated with such diverse conditions as migraines, mental illness (chiefly, depression), irritable bowel syndrome (IBS), heart disease, and osteoporosis.

Too much serotonin in the body can result in serotonin syndrome, a potentially life-threatening condition. Combining any drugs or supplements that can increase serotonin may increase a person’s risk of serotonin syndrome. Talk to your doctor before using any such substances.

Further Reading

About the Author

Ana Aleksic

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