Serotonin, also called 5-hydroxytryptamine (5-HT), is best known for the part it plays in mood and behavior.

But did you know that it also affects your sleep, appetite, digestion, and more? Low levels of serotonin can have wide-ranging effects on your mental and physical health.

Serotonin deficiency occurs when serotonin doesn’t act as well as it should in your body. This can happen if your body doesn’t produce enough serotonin or if it doesn’t use serotonin efficiently.

Scientists don’t yet understand exactly how serotonin works, what it does, and what causes low levels in the body. They’re also not certain exactly what the right levels are and how these might vary for different people.

Read on to learn what serotonin deficiency is and how it can affect your body.

Serotonin deficiency is a complex condition for which there are no diagnostic criteria and no clear tests. It’s generally discussed in terms of the symptoms that result, rather than the exact levels that might bring it on.

Serotonin deficiency has been linked to many physical and psychological symptoms. However, its exact role in any of them isn’t fully understood. Much research continues within the medical and scientific communities.

For example, researchers continue to debate the link between serotonin and depression. The connection between sleep and serotonin is also controversial. About the only thing researchers agree on is that serotonin’s function in the human body is complex and far-reaching.

Research has found that the overwhelming amount of serotonin in your body — 95 percent — is produced in the lining of your gastrointestinal (GI) tract. The remaining 5 percent is produced in your brain. There it acts as a neurotransmitter that carries signals between brain nerve cells (neurons).

Some research about serotonin has to do with its role in what is called the gut-brain axis. This is a communication line between the central nervous system and the enteric, or intestinal, nervous system. This effectively links the brain and the gut, giving rise to the name: gut-brain axis.

Research has shown that some of the serotonin produced in your gastrointestinal (GI) tract moves through your body in circulating platelets, or tiny blood cells, to help regulate important body processes such as:

  • immune response
  • bone development
  • digestion
  • cardiac function

Study of serotonin’s role in this gut-brain axis is relatively new, and ideas are changing rapidly. Much further research is needed.

Below, we’ll discuss the symptoms of serotonin deficiency and what may cause it. We’ll also outline ways to increase your serotonin levels.

Serotonin deficiency may be a contributing factor in many psychological and physical symptoms.

Psychological symptoms

Serotonin deficiency is associated with many psychological symptoms. These may include:

Low serotonin levels are also associated with various behavioral and emotional conditions, including:

Serotonin deficiency affects people differently. For example, research shows that people who haven’t experienced depression previously may not become significantly depressed with lower levels of serotonin, whereas those with a history of depression may.

Physical symptoms

Research has begun to show serotonin’s activity in increasing numbers of bodily processes, including:

  • metabolism
  • sleep
  • blood clotting
  • energy balance
  • digestion
  • body sugar balance
  • cardiac function
  • liver function
  • immune system response
  • pain production

Given serotonin’s wide scope of bodily functioning, it comes as no surprise that serotonin deficiency has been associated with many physical conditions, including:

Scientists are unsure what causes serotonin deficiency. Some research shows early life stressors might negatively affect the transport of serotonin in the body.

Other research shows that microbes in the gut help produce serotonin. This production might be disrupted when the microbiome, or gut bacteria as a whole, is disturbed because of stress, disease, diet, or other causes.

Both of these studies were done with animals, and researchers emphasized that further clinical research is needed.

Other potential causes of serotonin deficiency include:

  • chronic stress
  • nutritional deficiencies
  • digestion issues
  • certain drugs
  • hormone changes
  • lack of sunlight

Lower levels of serotonin are also thought to be related to a person’s particular biology, which may include:

Medical professionals generally don’t diagnose serotonin deficiency and choose instead to treat the symptoms.

This is because serotonin deficiency is a complex condition whose cause is very difficult to nail down. There are no diagnostic criteria, and it’s often unclear whether the symptoms cause the deficiency or the deficiency causes the symptoms.

There’s a test that measures the amount of serotonin in your blood, but medical professionals typically use this test only to check for tumors that produce serotonin outside of the brain. Your blood level of serotonin doesn’t accurately reflect the amount in your brain.

Serotonin generally can’t pass through the blood-brain barrier (BBB). This is a semi-permeable barrier surrounds your brain that lets some substances pass through, but not others.

This means that serotonin in your brain must be produced in your brain. For this reason, your body’s overall blood levels of serotonin are unreliable measurements of the amount of serotonin in your brain.

Urine tests are equally unreliable measures of your brain serotonin. They measure the amount of serotonin that your body is producing and how much is in your body, but they don’t measure the amount in your brain.

Your doctor may prescribe a urine test in combination with blood tests to test for serotonin-producing tumors, but not for serotonin deficiency.

If you think you have symptoms of a serotonin deficiency, it’s best to work with a medical professional to narrow down potential causes and develop a treatment plan. Read on to learn about potential treatments.

Your doctor will probably treat your symptoms of serotonin deficiency in one of the following ways.

Selective serotonin reuptake inhibitors (SSRIs)

Antidepressant medications called selective serotonin reuptake inhibitors (SSRIs) are often the first-line treatment of symptoms of serotonin deficiency such as depression and anxiety.

SSRIs help your body use serotonin more efficiently. They don’t create more serotonin.

Only a portion of the serotonin that your brain releases is used by your body. Some of the serotonin goes back into the cell that it came from. SSRIs block some of this reabsorption (reuptake) of serotonin, leaving more available for the body to use.

SSRIs commonly used include:

Natural remedies

SSRIs can take weeks to have an effect, and sometimes they may not work at all. Also, they can also cause a range of side effects that you may not tolerate well.

When SSRIs do work, they work very well and are a good option. Sometimes, if one SSRI doesn’t work, another one will.

If SSRIs aren’t the best treatment for you, you might ask your doctor about one of the following options.

Mood induction

Mood induction is an experimental treatment in which you create a positive mood by doing something you like or thinking about something that lifts your mood. Music, film clips, and imagery are common methods.

Exercise

Research shows that physical activity can raise brain serotonin levels by increasing both its production and its release in the brain.

Regular exercise is useful, but aerobic exercise is the most effective type of exercise for boosting serotonin levels. Aerobic exercises include:

  • walking
  • running
  • swimming

Diet

Research suggests a diet high in tryptophan may help increase serotonin levels in the body. Tryptophan is an essential amino acid in the body that is needed for the production of serotonin.

Significant amounts of tryptophan will probably not be absorbed into the brain from foods. Regularly consuming a variety of foods containing tryptophan may combine to make a difference, especially when combined with healthy carbs like whole grains or oatmeal.

Try these seven foods to start adding tryptophan to your diet.

Other substances that are thought to promote serotonin production in the body include:

Bright light

Research has shown that exposure to bright light — such as from the sun or a light box — may boost serotonin levels in your brain.

Serotonin deficiency can have far-reaching effects on both your mental and physical health. After more than 70 years of research, scientists and researchers still don’t entirely understand how serotonin is produced and used in the body.

If you have symptoms that make you think you might have a serotonin deficiency, talk with a doctor. Together, you can decide the best treatment options for you.

You might also try natural remedies, such as adding more sunlight, certain foods, and aerobic exercise to your lifestyle. These are best used as add-ons to medical treatment, not substitutions.

Serotonin deficiency is a complex condition, and a medical professional is the best person to guide you through it.