How Serotonin Regulates Body Functions

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 the neurotransmitter 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. Not only do the intestines produce almost all of the body's serotonin supply, but serotonin is required there to promote healthy digestion.

Elsewhere in the body, serotonin also 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 Does Serotonin Regulate?

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

Mood

Serotonin's effects in the brain could be considered its “starring role” in the body. As it helps regulate your 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.

The neurotransmitter'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, serotonin plays a starring role in treatments with 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. The neurotransmitter 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" of the chemical 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 has been debated by researchers, 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 your sleep cycle. Your body needs serotonin to make melatonin, so not having enough of the neurotransmitter (or having too much of it) can affect the pattern and quality of your sleep.

Your brain has specific sections 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.

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 arteriole) of the circulatory system to narrow. As they get smaller, blood flow slows.

This narrowing (known as vasoconstriction) and slowed blood flow are two crucial 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 a type of antidepressant that works on serotonin called selective serotonin reuptake inhibitors (SSRIs) is 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 doctor about other risk factors, such as having a family history of osteoporosis or smoking.

Sexual Function

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

Serotonin's influence on libido is also somewhat related to the neurotransmitter's relationship to another chemical in the brain: dopamine. For example, a 2017 study of women with hypoactive sexual desire disorder (HSDD) indicated 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, digestive, 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.

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 low serotonin 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 break down and absorb serotonin too quickly).

How to Increase Serotonin

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 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.

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 released. This process is called reuptake.

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

• Celexa (citalopram)
• Lexapro (escitalopram)
• Luvox (fluvoxamine)
• Paxil (paroxetine)
• Prozac (fluoxetine)
• Zoloft (sertraline)

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.

Popular SNRIs include:

• Cymbalta (duloxetine)
• Effexor (venlafaxine)
• Fetzima (levomilnacipran)
• Pristiq (desvenlafaxine)

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 epinephrine, which effectively increases the amounts available in the brain.

Examples of TCAs include:

• Anafranil (clomipramine)
• Asendin (amoxapine)
• Elavil (amitriptyline)
• Norpramin (desipramine)
• Pamelor (nortriptyline)
• Sinequan (doxepin)
• Surmontil (trimipramine)
• Tofranil (imipramine)
• Vivactil (protriptyline)

MAOIs, on the other hand, 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:

• Azilect (rasagiline)
• Emsam (selegiline)
• Marplan (isocarboxazid)
• Nardil (phenelzine)
• Parnate (tranylcypromine)

Food

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 the neurotransmitter.

Foods that are good sources of these key nutrients include:

• Bananas
• Beans (such as chickpeas, kidney, pinto, black beans)
• Eggs
• Leafy greens (such as spinach, kale)
• Nuts and seeds (such as walnuts, flaxseed)
• Oily, fatty fish (such as salmon, tuna, mackerel) 
• Probiotic/fermented foods (such as kefir, yogurt, tofu)
• Turkey

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 been linked to adequate serotonin levels (as the intestines make about 95% of your body's supply of the neurotransmitter).

Exercise

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

A workout 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 President's Council on Sports, Fitness, and Nutrition recommends that adults get at least 150 minutes of moderate-intensity cardio exercise each week plus two days of strength training.

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).

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 sunlight.

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 can also be helpful. Popular dietary supplements you might want to consider include:

• 5-HTP
• Probiotics
• Pure tryptophan
• SAMe (S-adenosyl-L-methionine)
• St. John's wort

Dangers of Too Much Serotonin

Always ask your doctor 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.

The symptoms of serotonin syndrome range from unpleasant to life-threatening and can include sudden swings in blood pressure, seizures, and loss of consciousness.

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 doctor. If your serotonin levels are a culprit, you are not alone and there are many treatment options available from medications to lifestyle changes.