Serotonin Metabolism: How Does It Affect Your Health?

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When people think of happiness hormones, many often think of “dopamine” and forget about the other happy hormone, “serotonin.”

Serotonin Metabolism: How Does It Affect Your Health?

Serotonin is a hormone that is also a neurotransmitter, which means it can carry signals between the cells of the nervous system (neurons). It is best known for its role in the nervous system and neuropsychological processes; however, serotonin regulates numerous other biological functions. 

Have you ever wondered what makes you feel full and stop eating? Serotonin is an appetite suppressor, and that is only one of its many roles.

Although serotonin is produced outside the central nervous system (CNS), it virtually modulates all human biological processes [1]. 

Serotonin modulates mood, appetite, anger, aggression, memory, sexuality, and practically every type of behavior.

a picture of good health

Almost every cell in the brain is affected by serotonin in one way or another. Low serotonin levels have been linked with anxiety, depression, mania, and others, making it a target for therapy in psychological disorders. The most potent class of antidepressants is that of drugs known as selective serotonin reuptake inhibitors (SSRI) [2].

Beyond the CNS, serotonin is involved in cardiovascular function, bladder control, bowel motility, and sexual health. It also plays a significant role in the gastrointestinal system. In fact, about 95% of the body’s serotonin is released into the gut [1]. 

Serotonin plays various essential roles in the body, from metabolism to pain control and bone density. 

  • Vascular: serotonin controls vascular resistance, blood pressure, homeostasis, and platelet function.
  • Cardiac: modulates heart function.
  • Pulmonary: serotonin helps control breathing through its effects on the brainstem and the lungs. 
  • Metabolism: it helps in energy balance and health of endocrine glands such as the pancreas and liver.
  • Gastrointestinal System: it controls satiety and regulates pancreatic enzymes.
  • Pain Control: serotonin regulates pain perception and processing. 
  • Genital and Urinary (genitourinary): serotonin prolongs ejaculatory latency, delays orgasm, and affects the bladder.
  • Bone: it regulates bone density.
  • Fat Tissues: serotonin regulates adipose tissue or fat.
serotonin metabolism

In this article, we will explore the metabolism of serotonin and its health implications.

Where & How Is It Made?

Serotonin is scientifically known as 5-Hydroxytryptamine (5-HT). It binds to receptors called 5-HT receptors in order to exert its functions. These receptors are widespread across the body and found on many different cells such as neurons, the cells of the GI tract, liver, pancreas, veins, arteries, etc. [3]. The abundance of serotonin receptors across many different types of cells in the body explains its multifunctional roles. 

Serotonin is biochemically produced in two steps from the amino acid tryptophan. The amino acid tryptophan is transformed to 5-hydroxytryptophan (5-HTP) then to 5-hydroxytryptamine (5-HT) or serotonin [5]. 

In the CNS, serotonin is synthesized in the neurons in limited quantities. Less than one in a million CNS neurons synthesize serotonin, the bulk of serotonin is produced outside the CNS [6]. This peripheral serotonin production mainly occurs in enterochromaffin cells, and to a lesser extent, in the platelets. Enterochromaffin cells are found alongside the lining of the digestive tract. And while enterochromaffin cells produce the bulk of the body’s serotonin, more than 90% of the body’s serotonin is stored in platelets [2].

Serotonin Metabolism Enzymes

Serotonin metabolism is primarily executed by enzymes of the outer mitochondrial membrane, monoamine oxidase (MAO). There are two subtypes of MAO; MAO-A, and MAO-B, widespread in the brain and peripheral tissues. 

The primary metabolism of serotonin is through MAO. MAO converts serotonin to 5-hydroxyindole acetaldehyde, which is metabolized by mitochondrial aldehyde dehydrogenase (ALDH2) to produce 5-hydroxyindole acetic acid, the metabolite of serotonin [7]. 

The availability of serotonin impacts serotonin metabolism, alongside the type of tissue and cells, the state of the tissue, and many other factors. 

serotonin metabolism

For example, in the brain, lowering the dietary intake of the amino acid tryptophan reduces the content of 5-HT in the brain and changes certain behaviors associated with serotonin [8].

In the lungs, in response to injury, 5-HT uptake from the blood is significantly reduced early on, which means that the metabolism of serotonin is shut down by decreasing serotonin itself in lung cells [9]. 

Serotonin: In Sickness & In Health

As we previously mentioned, serotonin is the primary target for treating psychological disorders. Serotonin disorders usually lead to mental disorders. The following is the list of mental disorders caused by serotonin imbalance [10,11,12]:

  • Major Depressive Disorder (MDD): one of the most critical mental disorders associated with altered serotonin levels. 
  • Mood Disorders: such as bipolar disorder.
  • Attention Deficient Hyperactivity Disorder (ADDH): multiple studies suggested a role for serotonin in ADHD.
  • Autism: hyperserotonemia Elevated whole blood serotonin was the first biomarker identified in autism. Recent studies suggest serotonin as a primary target for treatment for children with autism.
  • Eating Disorders: such as bulimia and anorexia. Alterations in brain serotonin contribute to eating disorders. 

Serotonin also affects many other physiological functions; here is a list of serotonin-related disorders beyond the nervous system [13,14]:

  • GI Disorders: serotonin receptors have been targeted for the treatment of diarrhea and constipation.
  • Irritable Bowel Syndrome (IBS): studies strongly suggest serotonin’s involvement in IBS.
  • Inflammatory Bowel Diseases (IBD): serotonin is reduced in IBD.
  • Inflammation: many inflammatory disorders are associated with a decreased serotonin expression, except in celiac disease, where serotonin levels are increased.
  • Obesity: peripheral serotonin production is increased in obesity.

How Can You Boost Serotonin Metabolism In Your Body?

  • Get out more: Recent studies suggest that bright sunlight exposure increases serotonin in the brain, which in turn explains seasonal depressions [15]. 
  • Exercise: Physical activity has been linked with increased brain serotonin [16].
  • Eat More Carbs: Carbohydrates increase the release of brain serotonin [17].

Serotonin can be manipulated by drugs such as the previously mentioned antidepressant drugs; however, serotonin toxicity, a life-threatening condition, has been linked to such antidepressants [2].

Serotonin Metabolism: Summing Up

Serotonin is a hormone and a neurotransmitter that affects our bodies in more ways than we can imagine. 

It plays many crucial roles in mental health as well as physical health. It is synthesized mainly in neurons and cells of the gut and derived from an amino acid called tryptophan.

Serotonin metabolism is dependent on many factors, such as the availability of tryptophan. We can naturally boost our serotonin levels by exercising, getting enough sunlight, and eating an adequate amount of carbs. If you are currently on antidepressants that target serotonin to increase its levels, please remember to take it as prescribed by your doctor since excess serotonin levels lead to serious health issues.



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