What is the role of serotonin?

Serotonin is scientifically known as 5-hydroxytryptamine (5-HT). In the human body, it works as a neurotransmitter and a hormone. 

A neurotransmitter is a chemical messenger that relays signals between nerve cells, helping communication within the central nervous system (CNS). In contrast, a hormone travels through the bloodstream to target distant organs or tissues, where it influences physiological processes. Serotonin plays both roles.

What does serotonin do?

Serotonin has a profound effect on many physiological and psychological functions in your body. Although the intricate ways serotonin affects your health are still not well understood, researchers agree that its roles are many and complex. 

Serotonin may affect the following body functions:

• Mood: Helps regulate feelings of happiness and well-being.
• Appetite: Affects feelings of hunger and fullness. 
• Sleep: Helps regulate sleep patterns. Serotonin produces melatonin, a hormone that controls the sleep-wake cycle.
• Other central nervous system effects: Plays a role in memory, stress and fear responses, pain perception, and learning. 
• Eye health: Affects dilation of your pupils and internal eye pressure.
• Heart health: Regulates blood clotting, heart contractions, and blood vessel narrowing and widening. 
• Gut health: Affects the speed of digestion, gut movement, and secretion of intestinal fluids.
• Endocrine and metabolic effects: Helps regulate insulin, fat storage, and pancreas functioning.
• Reproductive and urinary health: Modulates urination, uterine function, penile function, and maturation of oocytes, which are female eggs involved in fertilization. 

Low vs. high serotonin

Both low and high serotonin levels can have significant effects on your health and well-being. 

Low serotonin levels

A 2023 review describes that low serotonin levels may contribute to mood disorders such as depression. However, the authors emphasize that extensive research will help confirm the link between serotonin and mood. 

In addition to depression, a 2021 review notes that low levels of serotonin may lead to certain conditions such as:

• obsessive-compulsive disorder (OCD)
• impaired learning and memory
• reduced or heightened sense of pain (analgesia or hyperalgesia)
• problems with sleep, especially in terms of deep rapid eye movement sleep
• anxiety disorders
• attention deficit hyperactivity disorder (ADHD)
• autism spectrum disorders
• schizophrenia
• migraine

But again, more research will help better understand how serotonin levels may affect mental and physical health. 

High serotonin levels

A 2016 review explains that significantly high levels of serotonin may result in a condition called serotonin syndrome. 

The symptoms can be mild to life threatening. They may include: 

• nausea, vomiting, and diarrhea
• confusion and agitation
• twitching and anxiety
• elevated blood pressure (hypertension)
• high body temperature (hyperthermia)
• increased heartbeat (tachycardia)
• overactive reflexes (hyperreflexia)
• dilated pupils (mydriasis)
• erratic eye movements (opsoclonus)

Combining or taking high doses of certain drugs, including some antidepressants, increases the risk of serotonin syndrome.

What increases serotonin?

According to a 2019 review, your body produces serotonin in two places:

• 95% in the enterochromaffin cells, located in the gastrointestinal (GI) tract 
• 5% in the raphe nuclei, located in the brain

You may be able to boost serotonin levels in several ways:

• Eat pre- and probiotics: A 2016 review describes a link between your GI system and serotonin. Foods that support the healthy bacteria in your gut may boost serotonin. This includes probiotics from fermented foods like tempeh, kimchi, and yogurt and prebiotics from fibrous foods like oats, onions, bananas, and legumes. 
• Get light exposure: According to a 2015 study, bright and natural light exposure may increase your serotonin levels. You can use a light therapy lamp or spend time in the sun.
• Get regular exercise: A large 2017 review concludes that both long-term and short-term exercise increases serotonin levels in the body. 
• Eat tryptophan-rich foods: The 2016 review from above notes that your body needs tryptophan to make serotonin. It is an amino acid that works like a building block for protein. You can get it from foods such as eggs, chicken, milk, tofu, peanuts, and sesame seeds. 
• See a doctor: If you have OCD, depression, or anxiety, you may benefit from seeing a healthcare professional. They may recommend treatment like therapy or antidepressant medications to improve your condition and maybe boost your serotonin. 

What depletes serotonin?

Not adhering to the tips in the chapter above may lead to low levels of serotonin. Specifically:

• low exposure to light
• low physical activity
• a diet low in tryptophan 
• a diet low in gut-friendly foods like pre- and probiotics

Besides this, researchers are still exploring what might cause a serotonin deficiency. 

Medications that affect serotonin levels

A 2016 review describes the medications that influence serotonin levels. 

This includes certain antidepressants that increase serotonin levels in the brain to improve mood, including: 

• selective serotonin reuptake inhibitors:
  • fluoxetine (Prozac)
  • sertraline (Zoloft)
  • escitalopram (Lexapro)
• serotonin-norepinephrine reuptake inhibitors
  • duloxetine (Cymbalta)
  • desvenlafaxine (Pristiq)
  • venlafaxine (Effexor)
• monoamine oxidase inhibitors
  • phenelzine (Nardil)
  • tranylcypromine (Parnate)
  • selegiline (Emsam)

In addition, other medications may affect serotonin levels in your body:

• fenfluramine (Fintepla), used to treat seizures
• amphetamine dextroamphetamine (Adderall), used to treat ADHD and narcolepsy

It’s essential to use prescription medications only as instructed by a healthcare professional. Misuse or improper combinations of drugs may lead to adverse effects, including serotonin syndrome.

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Summary

Serotonin is a multifunctional neurotransmitter and hormone that helps regulate many physiological and psychological functions. 

For example, adequate serotonin levels likely improve emotional well-being, appetite regulation, and sleep patterns. On the other hand, low levels could lead to mood disorders like depression and anxiety.

Gut-friendly foods, light exposure, and medications are a few ways to boost your serotonin levels.

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