Serotonin is a powerful neurotransmitter that’s responsible for some of your body’s most important functions. While you’re probably familiar with its role in regulating mood, serotonin also affects your sleep cycle, appetite, and digestion, among other physical processes.

About 95 percent of the serotonin in your body is produced in the lining of your gastrointestinal (GI) tract, where it regulates the movement of your intestines. The remaining 5 percent is produced in your brainstem, where it transmits signals between nerve cells in your brain.

Serotonin deficiency occurs when your body doesn’t have enough serotonin activity. This can happen for several reasons. It’s associated with a range of physical and psychological symptoms.

However, it’s important to keep in mind that serotonin’s role in these symptoms, especially the psychological ones, isn’t fully understood.

For example, the relationship between serotonin and depression is still frequently debated within the medical community. The one thing everyone seems to agree on is that serotonin’s function is much more complex than previously thought.

Keep reading to learn more about the symptoms associated with serotonin deficiency and ways to increase your serotonin levels.

Serotonin deficiency may cause a range of psychological and physical symptoms.

Psychological symptoms

Serotonin deficiency is thought to be associated with several psychological symptoms, such as:

In addition, low serotonin levels are also thought to be associated with several psychological conditions, including:

Remember, doctors don’t understand the exact role of serotonin in these symptoms and conditions. Serotonin deficiency also seems to affect men and women differently.

For example, a 2007 study found that reduced levels of serotonin in the brain caused depression and other mood changes in women. Male participants, however, became more impulsive and didn’t report any mood changes.

A more recent study showed that serotonin deficiency may affect mood differently in people who’ve previously had depression compared to those who’ve never had it. People who haven’t had depression may not become significantly depressed when serotonin is deficient.

Physical symptoms

Given its role in many of your body’s vital functions, serotonin deficiency may also cause several physical symptoms, including:

Researchers aren’t sure about the exact causes of serotonin deficiency. Some people may simply produce less than others.

Other potential causes include:

  • having fewer serotonin receptors
  • having serotonin receptors that don’t effectively receive serotonin
  • serotonin breaking down or being absorbed to soon
  • low levels of L-tryptophan, vitamin D, vitamin B-6, or omega-3 fatty acids, which your body needs in order to produce serotonin

In addition, your life experiences may also play a role.

For example, a 2009 study found that participants who’d experienced childhood abuse had lower brain serotonin transporter binding potential than those who weren’t abused. This means that those who had been abused had less serotonin activity.

It’s hard to diagnose a serotonin deficiency because there’s no way to accurately test the amount in your brain, and there are no specific diagnostic criteria.

While there is a test that measures serotonin in your blood, it’s generally only used to check for serotonin-producing tumors outside of the brain. Also, blood serotonin levels don’t necessarily reflect the levels in your brain.

Steer clear of neurotransmitter urine tests that are available online. A 2010 analysis debunked claims that these tests can help to diagnose serotonin deficiency in the brain.

Your brain is surrounded by a membrane called the blood-brain barrier (BBB). This membrane is semi-permeable, meaning it lets some things through but not others. Serotonin is one substance that can’t pass through the BBB.

This means that serotonin in your brain generally must be produced in your brainstem, making the levels in your blood and urine an unreliable measurement of the amount in your brain.

If you think you have symptoms of a serotonin deficiency, it’s best to track your symptoms for a few weeks and work with your doctor to narrow down a diagnosis.

Regardless of what’s causing a serotonin deficiency, there are a few proven ways to increase serotonin functioning, both in your brain and the rest of your body.

Selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are antidepressant medications that help your body use serotonin more efficiently.

They do this by inhibiting serotonin reuptake by the presynaptic receptors in order for serotonin to be more available to bind to the postsynaptic receptors. This results in more serotonin in the synapses between the ends of neurons, increasing the amount that’s available to use.

In other words, SSRIs don’t create more serotonin, but rather help your body use what it has more effectively.

Some common SSRIs include:

Natural remedies

Like any type of medication, SSRIs don’t work for everyone. In some cases, they can also cause a range of unpleasant side effects.

If SSRIs aren’t an option for you, there are several effective natural remedies you can try:

Mood induction

This refers to intentionally creating a happy mood by doing something you love or thinking about things that you know will make you happy.

While this might sound easier said than done, a 2007 study found that doing so increased serotonin levels in the brain.

Exercise

Multiple studies have suggested that physical activity improves brain serotonin levels by increasing both the production and the release of serotonin in the brain.

The most effective exercises seem to be aerobic ones, such as walking, running, or swimming.

Diet

Consume more foods that contain the nutrients your body needs to produce serotonin.

These would include those with:

Try these seven serotonin-boosting foods to get started.

Bright light

Several studies have shown that exposing yourself to bright light — either from the sun or a light box — may increase the level of serotonin in your brain.

Not having enough serotonin can have range of effects on your overall mental and physical health. Yet researchers still have many questions about how serotonin works in both the brain and the rest of your body.

If you think you have a serotonin deficiency, it’s best to talk with your doctor to get a better idea of what might be causing your symptoms.

You can also try some simple but effective natural remedies, such as going for regular walks outdoors and adding certain foods to your diet, to see if your symptoms improve.