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Serotonin Level: Functions, Uses Side Effects, Source, Serotonin vs. Dopamine & More

Serotonin is a chemical that is often termed a hormone. Serotonin's normal level is produced by nerve cells and acts as a neurotransmitter, relaying messages between brain cells.

The other name for serotonin is 5-hydroxytryptamine or 5-HT.

Serotonin is also labeled as the ‘happy’ hormone owing to its role in maintaining mood, feelings of well-being, and anxiety relief. Too little serotonin in the brain can induce depression. However, the definition of serotonin as an anti-depressant only is not fair because the neurotransmitter plays a significant role throughout the body.

Optimal levels of serotonin are important for maintaining mood, sleep patterns, and digestion. Though the hormone is linked to brain functioning, serotonin contributes to many other body functions. These include wound healing, preserving bone health, regulating bowel movements, and so on.

Serotonin Level Functions, Uses like Side Effects, Source, Serotonin vs. Dopamine

Serotonin vs. dopamine

Dopamine is a neurotransmitter. It is called the happy hormone alongside serotonin.

This neurotransmitter is associated with feelings of motivation and reward. Its deficiency causes low self-esteem, a feeling of helplessness, and loss of pleasure in activities that previously attracted a person.

Serotonin, on the other hand, is a mood-boosting hormone. It works by positively processing the emotional response over time.

Dopamine is the neurotransmitter that creates addictive patterns in the brain (because of its reward-based response) and is responsible for the withdrawal effects of a substance.

Both of these chemicals affect the digestive system, dopamine being the insulin stimulator while serotonin regulates gut functions.

Dopamine is linked to wakefulness while serotonin has a dual effect as regards sleep (details explained later in the article).

The source of the body’s serotonin

Serotonin is often tagged as being a brain-specific hormone. However, the chemical is also found throughout the central nervous system. It is also produced by blood platelets. The digestive system is the major source of this ‘happy’ hormone.

Did you ever wonder why eating certain foods like nuts, cheesy pizza, steaks, make you happy? These food items are rich sources of tryptophan, one of the essential amino acids.

Amino acids are building blocks of proteins, which in turn form essential structural components of many cells, hormones, and neurotransmitters.

There are eleven non-essential amino acids, which the body synthesizes in abundance.

Nine amino acids are essential, meaning the body cannot synthesize them and they must be taken from an outside source including diet and nutritional supplements.

Tryptophan, being an essential amino acid, must be taken via food. After being absorbed, tryptophan is converted in the digestive tract into serotonin, which is then released into the bloodstream to reach everybody cell.

Some of the best dietary sources of serotonin are;

  • Salmon
  • Eggs
  • Nuts and seeds
  • Poultry
  • Turkey
  • Tofu and soy
  • Milk and cheese
  • Red meat
  • Pineapple

Green tea, probiotics, and vitamin D help boost tryptophan and increase its conversion to serotonin.

What does serotonin do?

Serotonin is a natural stabilizer of mood. Besides that, it impacts every part and function of your body. That includes motor abilities (movements and functions muscles), sleeping, eating, and digesting. Serotonin levels are directly proportional to our emotional health. The chemical contributes significantly too;

  • Maintain mood; high levels of serotonin increase the neuronal activity in the brain and vice versa. Serotonin is also called the mood hormone owing to its contribution to improve mood and induce feeling of happiness.
  • Cut back depression; owing to its mood elevating effects, serotonin is linked to effectively reduce depressive thoughts and feelings.
  • Alleviate anxiety; the hormone makes you calmer and happier thereby making you less anxious and restless.
  • Contributes to bone health; the relationship of serotonin and bone health is complex yet interesting.

Two distinct genes produce serotonin at two different sites; peripheral in the gut and elsewhere and central in the brain. The hormone produced at these sites plays an opposing role regarding bone health.

Serotonin synthesized peripherally inhibits bone formation. On the other hand, serotonin produced in the brain exerts a positive effect on bone formation and cuts back at bone resorption. This effect is dominant as compared to the peripheral effect on bone health.

  • Maintain muscle function; serotonin contributes to motor skills as is evident by the fact that it positively impacts the skeletal muscle growth, differentiation and metabolism. 
  • Regulate sleep pattern and quality; another intriguing relationship of serotonin is with sleep pattern. Serotonin is the precursor of sleep hormone, melatonin. However, the actual role of serotonin is dual; it helps maintaining sleep as well as contributes to wakefulness.

The effects of serotonin on sleep depend on many factors. The source of serotonin in the brain and the type of receptor the hormone binds to are some primary limiting factors.

For example; high levels of serotonin in the dorsal raphe nucleus of the brain is linked to wakefulness. However, a gradual build-up of serotonin in the same area is linked to sleep induction with time.

Serotonin is also linked to reducing the duration of REM sleep patterns. This is shown by the fact that individuals who take selective serotonin reuptake inhibitors (SSRIs) experience less REM sleep.

  • Accelerates wound healing; serotonin is found in blood platelets. At the time of injury, the serotonin stimulates the blood platelets to accumulate at the site of injury. This encourages blood clot production, stops bleeding, and speeds wound healing.

Serotonin has a vasoconstrictive effect on small vessels. This helps to slow down the blood flow through the local vessels at the site of injury and promotes the accumulation of platelets and the formation of a blood clot.

  • Induce nausea; high levels of serotonin induces nausea that may or may not result in vomiting. This fact is manipulated in cancer therapy to control and manage the nausea and vomiting, a side effect of chemotherapy.

Similarly, serotonin blocking drugs help manage nausea associated with post-radiation, post-surgery, hyperemesis gravidarum, and acquired immunodeficiency syndrome or HIV.

The nausea-inducing effect of serotonin has a protective effect on the gut lining. When a noxious stimulus enters the gut, the serotonin production from the local cells is increased. High levels of serotonin in the gut increase peristalsis and speed up the removal of the toxic material from the body.

  • Role in sexual function; increased levels of serotonin have a dampening effect on sex drive and vice versa. This is often observed as a side effect of anti-depressants like SSRIs that increase the levels of serotonin in the body. That is why serotonin agonists are suggested to treat premature ejaculation in men.
  • Regulate bowel movement; being present primarily in the cells of stomach and intestine, the hormone caters to function and movement of smooth muscle of the intestine.
  • Serotonin and appetite; serotonin plays an active role in energy homeostasis in the body. The hormone levels of centrally-produced (brain) serotonin has inverse relationship with appetite; increased levels suppress appetite. Serotonin produced in the brain increases the sympathetic drive to fatty tissue and promotes fat burning and energy expenditure.

This fact is being utilized in creating and designing safer anti-obesity drugs.

On the other hand, there is increasing evidence of serotonin regarding improved nutrient absorption and its storage in different organs including the liver. The glucose and fatty acids stimulate the release of serotonin from the duodenum. Gut peristalsis is increased in response that results in enhanced absorption from the small intestine.

Serotonin also enters the bloodstream and stimulates the release of insulin. The effects of serotonin in enhancing the liver lipid storage processes and decreasing lipid breakdown are active topics of research.

Body temperature

Breathing rate

What are the body’s normal levels of serotonin?

The normal levels of serotonin are dependent on the method used to measure the chemical as well as the location from where the sample is obtained. So there is no definite benchmark for the body’s serotonin levels.

However, an average value is placed at 101–283 nanograms per milliliter (ng/mL) in the blood.

Causes for imbalances in serotonin levels

Low levels of serotonin are more common than high ones. There are two causes of low serotonin levels in the body;

  • Deficient intake of serotonin
  • Inefficient use of available serotonin in the body

Diet deficient in tryptophan may result in low serotonin levels. This may also happen in cases of low intake of vitamin B6 and vitamin D as well as omega-3 fatty acids.

Besides physical causes, life experiences are also suggested to play a role in serotonin functioning. For example, a 2019 study concluded that participants who had experienced abuse in childhood had lower brain serotonin transporter binding potential as compared to those who did not have any such experience. The low potential means low serotonin functioning and more chances of depressive episodes.

The inefficient use of serotonin may happen if the serotonin receptors in the brain are not in sufficient numbers. It may also happen that the receptors are not working effectively. In such a case, the serotonin, despite being in sufficient quantities, may not work efficiently.

On the other hand, certain conditions may result in increased serotonin levels. For example carcinoid syndrome. The syndrome presents with a group of symptoms that arise due to tumors of;

  • small intestine
  • bronchial tubes
  • appendix
  • colon

Symptoms of low serotonin levels

Serotonin deficiency results in physical and psychological symptoms owing to the fact that the chemical is released both centrally and peripherally.

It must be appreciated that serotonin deficiency may exhibit itself differently in men and women. For example, low levels are linked to depression in women while in men it causes a tendency to impulsive behavior instead of depressive thoughts.

Similarly, the depressive effects of low serotonin are exhibited differently in people who have had a previous depressive episode than those who never had low mood and behavioral changes.

The psychological symptoms of serotonin deficiency and some psychological behavioral conditions are;

  • anxiety
  • depressive feelings and thoughts
  • aggressive behavior
  • impulsiveness
  • insomnia
  • irritability
  • low self-esteem
  • lack of appetite
  • poor memory
  • eating disorders
  • obsessive-compulsive disorder
  • panic disorder
  • post-traumatic stress disorder
  • social anxiety disorder

The physical changes related to serotonin deficiency include;

  • increased carbohydrate cravings
  • weight gain
  • fatigue
  • nausea
  • digestive issues or gastrointestinal motility problems (irritable bowel syndrome and constipation)

Symptoms of high serotonin levels

An excess of anything is bad and that is true for serotonin the ‘feel-good’ hormone as well.

Serotonin syndrome is a condition that results from an excess accumulation of the hormone in the body. This may happen as a reaction to a newly introduced serotonin agonist drug or increasing the dose of a serotonin-boosting medication.

A combination of different prescriptive medicines may also cause a negative reaction increasing the serotonin levels in the body.

Anti-depressants (SSRIs, SNRIs, tricyclic antidepressants, monoamine oxidase inhibitors) taken with analgesics and drugs for migraine (almotriptan, naratriptan, sumatriptan) may result in serotonin syndrome.

Certain prescriptive antibiotics, antivirals, and anti-emetic may also increase the serotonin levels to dangerous levels if taken with anti-depressants.

Medicines for cold and cough (Robitussin DM and Delsym) and herbal supplements like St. John’s wort and ginseng also tend to increase the levels of serotonin in the body.

Illegal substances and drugs like LSD, ecstasy (MDMA), cocaine, and amphetamines are also linked with serotonin syndrome.

It is always better to consult your doctor if you are currently taking serotonin-enhancing drugs before taking any new medication protocol.

The symptoms of serotonin excess range from mild to severe and include the following;

  • Confusion and disorientation
  • irritability
  • anxiety
  • headache
  • muscle spasms and rigidity
  • tremors
  • shivering
  • diarrhea
  • rapid heartbeat
  • high blood pressure
  • nausea
  • hallucinations
  • overactive reflexes
  • dilated pupils
  • goose bumps

The severity of serotonin syndrome is presented as;

  • High grade fever
  • twitching of muscles
  • loss of muscle agility along with muscle stiffness
  • high blood pressure
  • irregular and rapid heartbeat
  • seizures
  • unresponsiveness
  • coma
  • seizures

The muscle spasms of serotonin syndrome are severe enough to result in the breakdown of muscle tissue. This burdens the kidney and may damage the organ seriously. It is a serious complication of serotonin syndrome which requires temporary paralysis of the muscles. This can only be done in a hospital setting with the insertion of a breathing tube and a respirator.

Any suspicion of serotonin syndrome should call for prompt treatment and management. This includes;

  • withdrawal of any medication that resulted in serotonin increase
  • intravenous fluids maintenance to counteract dehydration and fever
  • medications to relieve muscle stiffness
  • administration of serotonin-blocking medications

How to maintain healthy levels of serotonin?

Serotonin levels can be improved via medication. There are natural ways to improve or preserve the levels of serotonin. Here is a look at them;

  1. Use of Selective serotonin reuptake inhibitors (SSRIs)

SSRIs are the first-line therapeutic drugs to treat the depressive symptoms of low serotonin levels. 

These drugs act by blocking the reabsorption of serotonin. Serotonin when released for signaling in the brain between two nerve cells must be reabsorbed and recycled before the next signal initiation. 

When the reuptake is inhibited, it increases the level of serotonin in a nerve synapse, the space between the two nerve cells.

Common examples of these drugs are

  • Prozac
  • Zoloft
  • Celexa
  • Lexapro
  • Luvox
  • Paxil
  • Prozac

Some serotonergic drugs act the same way besides being a partial agonist of the 5HT-1a receptor. These are called serotonergic antidepressants. For example; Trintellix and Viibryd.

  • Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)

These drugs work in a similar way as the SSRIs. They not only block the reuptake of serotonin but also work to increase norepinephrine, which is another neurotransmitter involved in mood regulation.

SNRIs are also termed as dual-acting antidepressants as they affect both serotonin and norepinephrine.  

Some examples of SNRIs include;

Popular SNRIs include:

  • duloxetine
  • venlafaxine
  • levomilnacipran
  • desvenlafaxine
  • Tricyclics (TCAs) and Monoamine Oxidase Inhibitors (MAOIs)

These antidepressants are old-timers and are not preferred because of their side effects.

TCAs cut back on the reabsorption of serotonin and norepinephrine. Some examples of TCAs include;

  • Anafranil
  • Elavil
  • Norpramin
  • Pamelor

MAOIs block the effects of the monoamine oxidase enzyme. This enzyme is responsible for the breakdown of serotonin, epinephrine, and dopamine thereby resulting in an increase in the levels of these hormones in the brain. Examples of MAOIs are;

  • Selegiline
  • isocarboxazid
  • phenelzine

What are natural ways to improve serotonin levels?

According to the Journal of Psychiatry and Neuroscience, some natural ways to maintain healthy levels of serotonin include;

  1. Exposure to bright light

Seasonal depression is related to the length of the day and the light exposure of a person. That is why light therapy is suggested to improve symptoms of seasonal depression and other types.

Sunlight also boosts the levels of vitamins which is important for converting tryptophan to serotonin. Spending some time in sunlight every day improves mood and contributes to health as well.

If your lifestyle does not allow for spending outdoor time, seek light therapy to compensate for the daily dose of sunlight.

  • Exercise

Regular physical activity can have mood-boosting effects, particularly aerobic exercise. Exercise helps boost serotonin levels. The health benefits of regular moderate exercise extend to all bodily functions including cardiovascular and metabolic health.

Health experts suggest at least 150 minutes of moderate-intensity cardio exercise per week. Adding strength training to the exercise schedule upgrades the benefits a step further.

  • A healthy diet

Foods that have a direct impact on serotonin levels, as well as those that help in the synthesis of serotonin, should be a regular part of the diet. Tryptophan rich foods include

  • eggs
  • cheese
  • turkey
  • nuts and seeds as walnuts and flaxseeds
  • salmon and other fatty fish as tuna, mackerel
  • pineapple
  • green leafy vegetables
  • bananas
  • beans as chickpeas, black beans, pinto, etc
  • Probiotic rich or fermented foods such as kefir, yogurt, tofu
  • turkey

A balanced diet provides the adequate raw material, tryptophan, vitamin B6, vitamin D, and omega-3 fatty acids, for serotonin synthesis in the body. A fiber-rich diet preserves and maintains the friendly bacteria in the gut which ultimately results in healthy serotonin levels with the gut being the primary source of the hormone.

  • Meditation

Meditating works in conjunction with exercise to boost your serotonin levels. Meditative exercises help relieve stress and improve the outlook on life in general, which has a significant impact on serotonin and its receptor-binding potential in the brain.

  • Massage

Massage therapy is linked with the release of serotonin. It also decreases the stress hormone cortisol.

Study results published in the International Journal of Neuroscience (2004) concluded that a massage session of 20 minutes increased the serotonin levels by 28% and dopamine levels by 31% in pregnant women.

  • Supplements

Supplements may complement your dietary sources of tryptophan and other necessary ingredients. These include;

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

However, the FDA does not regulate dietary, herbal or other nutritional supplements. So a vigilant consultation with your doctor is a must before supplementing your diet. This is particularly true if you are already taking antidepressants or other serotonin-boosting medications.

Abdur Rashid
Medically Reviewed By Abdur Rashid
MSC Public Health, MCSP, MHCPC
BSC (Hon) Physiotherapy
Consultant Neuro-spinal & Musculoskeletal Physiotherapist

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