Our body produces several chemicals that make us feel good. Serotonin is one of them. However, balanced serotonin levels are essential for other bodily systems, not just mood. The chemical is involved in digestive health, the sleep-wake cycle, appetite regulation, sexual function, body temperature regulation, wound healing, cognitive skills, and more.

This article explains what serotonin is, how it affects our overall health and behavior, and how to maintain adequate levels.

What Is Serotonin?

Serotonin is a neurotransmitter – a chemical substance that sends signals from nerves to other nerves or cells. It essentially "instructs" nerve cells on how to respond to stimuli, affecting functions such as mood regulation, sleep, and appetite.

In addition to its role in the brain, serotonin acts as a hormone when produced outside the nervous system, particularly in the gastrointestinal tract. About 90% of the body’s serotonin is found in the digestive system, where it helps control gut movements and can affect processes like digestion and blood clotting.

A serotonin imbalance is associated with a host of unpleasant symptoms, most commonly depression and anxiety. Because of its strong impact on mood and behavior, treatments for many psychiatric and neurological conditions rely on modulating serotonin production. Imbalances in gut serotonin can lead to digestive issues such as irritable bowel syndrome (IBS) and constipation and may indirectly influence mood and mental health through the gut-brain axis. Research also suggests links between gut serotonin levels and conditions like obesity and osteoporosis.

Where Is Serotonin Produced?

Serotonin is synthesized from the essential amino acid tryptophan, which enters our bodies through food. About 5% of serotonin is synthesized in the brain, where it acts as a neurotransmitter, sending signals via neurons.

About 95% of serotonin is produced in the intestine, where it acts as a hormone that aids digestion and is involved in regulating intestinal movements (peristalsis). Once released into the blood, most of serotonin is absorbed by platelets. The rest is metabolized by the liver and excreted through urine or degraded in the lungs.

What Does Serotonin Do?

Serotonin regulates various bodily activities, including:

Mood and Behavior

Serotonin receptors are located in multiple brain regions which govern our behavior. Depending on which receptors are activated and how much serotonin is transmitted, the neurotransmitter affects our feelings and expressions of anger, aggression, fear, reward processing, and almost every other behavior. Normal serotonin levels contribute to emotional stability and increase happiness.

Note: Learn more about the relationship between hormones and mental health.

Cognitive Function

Many serotonin receptors are in the brain regions that regulate cognitive processes. Scientists speculate that serotonin concentrations and transmission are linked to memory, learning, concentration, decision-making, problem-solving, spatial navigation, and other cognitive skills.

Heart Function

Serotonin is involved in several cardiac processes, from heart development to heart rate regulation. It may play a role in the development of cardiovascular diseases like hypertension and atherosclerosis. Scientists are exploring serotonin-modulating drugs as promising treatment options.

Sleep

Serotonin is a precursor to melatonin, the key hormone regulating sleep. It is involved in controlling the circadian (sleep-wake) rhythms and its levels affect sleep onset and depth. An imbalance in serotonin levels can lead to difficulty falling asleep, interrupted sleep patterns, insomnia, and other sleep disorders.  

Appetite

Serotonin suppresses appetite and regulates food intake by influencing hunger signals and energy balance. It is considered a promising aid in weight loss and obesity treatments due to its effects on satiety and metabolism.

Digestion

One of serotonin’s key functions is regulating the movement of food through the digestive system. Disrupted serotonin signaling is associated with gastrointestinal disorders, such as irritable bowel syndrome, chronic constipation, and chronic diarrhea.

Body Temperature

The activation of different serotonin receptors causes an increase or a decrease in body temperature. With other chemicals, such as adrenaline and noradrenaline, serotonin maintains a balanced thermoregulation system.

Wound Healing

When an injury occurs, platelets are activated at the injury site and release serotonin, which constricts blood vessels to limit blood flow and reduce blood loss. Serotonin also enhances the formation of blood clots to close the wound and stimulates fibroblasts – cells that produce collagen to form new tissue.

Sexual Drive

Serotonin has a complex effect on libido, depending on which receptors are activated. Studies show that high serotonin levels inhibit sex drive, while low levels are associated with increased sexual desire. That is why low libido is one of the side effects of SSRIs (selective serotonin reuptake inhibitors), anti-depressants drugs that increase serotonin levels.

Note: Learn what other hormones and factors contribute to low sex drive in men and how to treat it.

Other Functions

The list of functions modulated by serotonin is long and includes breathing, eye health, bone density, immune function, stress response, pain sensitivity, embryonic development, and more. This chemical plays a crucial role in maintaining homeostasis across multiple systems, influencing both physical and mental wellbeing.

How Do I Know If I Have Low Serotonin?

Low serotonin levels are typically associated with mood disorders like depression and anxiety. It can also lead to other undesirable mental and psychological states, including:

• Irritability
• Frustration
• Phobias
• Panic attacks
• Schizophrenia
• Cognitive decline
• Dementia
• Lack of energy
• Muscle pain
• Digestive disorders
• Sleep problems, etc.

What Reduces Serotonin?

Not enough serotonin receptors or ineffective usage of serotonin by the receptors are the direct causes of low serotonin. They are affected by the following factors:

• Genetics
• Chronic stress
• Nutritionally poor diet
• Environmental toxins
• Lack of sunlight
• Hormonal imbalances
• Alcohol and nicotine
• Certain medications

How to Check Serotonin Levels?

There is no reliable blood test that accurately evaluates overall serotonin levels. The following procedures help doctors establish if a patient has a serotonin imbalance.

• Physical examination – Medical providers first physically examine the patient and discuss their symptoms, genetics, medical history, medications, and other factors that may signal serotonin deficiency.
• Blood and urine tests – Testing the level of certain vitamins and nutrients required for serotonin synthesis can help determine serotonin levels. Doctors can also check hormones that affect serotonin release, such as estrogen, testosterone, cortisol, thyroid hormones, etc.
• Other specialized tests – Doctors may order an image CT scan, X-ray, spinal tap, and other specialized tests to exclude conditions that produce similar symptoms to those of the serotonin syndrome (elevated serotonin levels).

How to Increase Serotonin?

If you recognize symptoms of decreased serotonin, try natural ways of enhancing it.

Regular Exercise

Exercise is one of the best ways to boost serotonin levels because it has no side effects (like medications) and improves other health markers. Only 20-30 minutes of moderate physical activity daily, such as jogging or swimming, can increase the concentrations of this feel-good hormone.

Diet Modification

Eating more foods with tryptophan, serotonin’s precursor, may help improve serotonin levels in the blood. Sources of tryptophan are salmon, eggs, nuts, seeds, dairy products, soy products, whole grains, and legumes.

Light Therapy

Exposure to sunshine or light lamps for at least 10-15 minutes daily is associated with an increase in feel-good hormones, including serotonin. Light therapy is used in countries with low amounts of natural light to treat patients with SAD (seasonal affective disorder) and depression.

Stress Relief

Chronic stress can damage our health in many ways. It can lead to inflammation, hormonal imbalances, insulin resistance, and more severe diseases. It can also disrupt serotonin release. Engage in stress-relieving activities, such as meditation, yoga, relaxing music, and daily walks to counter the effects of elevated cortisol.

Note: Learn how to naturally lower cortisol levels and reduce the risk of stress-induced health problems.

Medications

Selective serotonin reuptake inhibitors (SSRIs) are the first-line treatment for moderate to severe symptoms of serotonin deficiency, such as depression, anxiety, obsessive-compulsive behavior, eating disorders, etc. Prozac is one of the best-known SSRIs. These medications work by blocking the reabsorption (reuptake) of serotonin in the brain, increasing its availability and concentration. While SSRIs are effective, they are potent medications and carry a black box warning due to the increased risk of suicidal thoughts, particularly in young people. Always take them only under a doctor's supervision and recommendation.

Other serotonin-increasing medications include serotonin norepinephrine reuptake inhibitors (SNRI), monoamine oxidase inhibitors (MAOI), tricyclic anti-depressants (TCA), and 5-HT receptor agonists. These medications are often prescribed for patients who don’t respond to SSRIs or to treat conditions such as migraines (5-HT receptor agonists).

Supplements

Supplements that may promote serotonin synthesis include:

• Probiotics – They help improve gut microbiota, potentially creating a healthier environment for serotonin synthesis.
• Tryptophan – Like tryptophan-rich foods, tryptophan supplements may promote serotonin synthesis. These supplements contain much higher concentrations than food and provide quicker results.
• St. John’s wort – This herb is a natural serotonin reuptake inhibitor. It also helps raise levels of other hormones that improve mood.
• B vitamins – They are essential in forming serotonin, especially B3 and B6. The vitamin B complex supports brain function and healthy energy levels.
• Vitamin D – It may help promote serotonin and melatonin synthesis, regulating sleep, mood, and other mental health parameters.

What Happens if Serotonin Levels Are Too High?

Serotonin syndrome or serotonin toxicity is a condition where patients suffer from excessive serotonin activity and associated symptoms. They include:

• Tremor
• Increased reflex response
• Uncontrollable jerking movements
• Increased heart rate
• Abnormally dilated pupils
• Excessive sweating
• Rapid breathing
• Overheating
• Vomiting
• Agitation
• Excitement
• Insomnia
• Confusion
• Anxiety

Serotonin syndrome can be caused by a reaction to a certain medication or taking higher doses than prescribed. It can be life-threatening if severe symptoms are not treated promptly.

How to Lower Serotonin?

If you experience serotonin toxicity, visit your doctor, or go to the ER immediately. The treatment typically involves the following:

• Stopping the medication that is causing the symptoms.
• Muscle relaxants or medications that paralyze the muscles.
• Serotonin antagonists, which block serotonin receptors.
• IV therapy to provide immediate symptom relief, helping to treat dehydration, fever, and other symptoms.
• Medications that lower heart rate and blood pressure.

Conclusion

Serotonin is an essential molecule that regulates nearly every behavioral and many other functions in our body. Disruptions in serotonin concentrations can lead to health problems, particularly those related to mood and mental health.

Healthy lifestyle habits are the first step in supporting healthy serotonin levels. Seek medical help if you suspect you’re suffering from a serotonin imbalance.