Serotonin deficiency

Serotonin Deficiency: Causes, effects & how to fix low serotonin

Serotonin (also known as 5-hydroxytryptamine or 5-HT) is among the most widely distributed chemicals in the human body. It has a diverse array of functions, some of which you may find surprising; serotonin is involved in everything from regulating mood and promoting learning to aiding with digestion and blood clotting. It is found everywhere from the brain to the bowels to your bloodstream.

Simply put, serotonin is an extremely important chemical for the proper functioning of the human body.

As you might imagine for such a vital neurotransmitter, a serotonin deficiency can be extraordinarily problematic. Low serotonin levels can have a devastating effect on a wide range of physiological functions. Specifically, serotonin deficiency is associated with:

  1. Anxiety
  2. Panic
  3. Low mood
  4. Depression
  5. Carbohydrate cravings
  6. Compulsive behaviors
  7. GI distress/discomfort
  8. Sleep disruption
  9. Insomnia
  10. Sexual dysfunction

That is a staggering range of effects for a single deficiency to have, but it’s true; low serotonin levels can negatively impact all of these things. Having chronically low serotonin levels can be difficult to reverse quickly too, so it’s important to not let serotonin deficiencies go untreated!

So what are the signs of serotonin deficiency? What causes a serotonin deficiency? How do you raise serotonin levels? Does low serotonin always cause depression and anxiety? Do any supplements help with serotonin levels?

In this article, I’ll answer all of these questions and more. But before I do, I’ll explain what serotonin is and what it does in the body.

What is serotonin?

As mentioned above, serotonin is one of the body’s most important neurotransmitters in the human brain, and in the human body more widely. Specifically, it is a monoamine neurotransmitter, which means it has a particular structure (other monoamine neurotransmitters are dopamine and norepinephrine). The proper name of serotonin is 5-hydroxytryptamine, although in the medical literature you will often see it written as 5-HT.

Serotonin is prevalent throughout the central, peripheral and enteric nervous system; this last one is the nervous system found in the gut which controls digestion among other things. In fact, many people are surprised to find out that most of the body’s serotonin is found in the gut. More on this later!

What is serotonin

While most of the body’s serotonin is found in the gastrointestinal tract, large quantities are produced in the brain; specifically, serotonin synthesis in the brain occurs in the Raphe nuclei located in the brainstem. It is also produced by Merkel cells located in the skin, and it can be found in your blood platelets (where it acts as an agonist to other plateletes, helping with clotting).

That’s what serotonin is, but what about what serotonin does?

What does serotonin do?

Serotonin’s role in the body is multifaceted and extremely complex. It is involved in a wide range of bodily functions, both mental and physical: serotonin is thought to underlie many sleep problems, mental illnesses, cognitive issues, and general well being. Due to its complex nature, it is best to understand serotonin by looking at its mental and physical effects separately.

Serotonin and mental health

Serotonin is best known as one of the “happy” neurotransmitters. It does indeed have a massive effect on mood and mental health. Serotonin is largely responsible for producing feelings of joy, contentment, satisfaction, empathy, and euphoria. It is heavily implicated in social bonding; studies have found that serotonin manipulation alters social behavior and the desire to interact with others[1]. This is how drugs such as MDMA work: MDMA is serotonin receptor agonist, which is why it produces feelings of intense euphoria and empathy.

Since it can directly affect empathy, contentment and social cohesion, serotonin obviously has a tremendous effect on anxiety, depression and aggression.

Serotonin, anxiety and depression

Selective Serotonin Reuptake Inhibitors is one of the most commonly used antidepressant drug classes in the world. These antidepressants work by inhibiting the reuptake of serotonin by the presynaptic cell; this by extension increases the amount of serotonin in the “synaptic cleft” (the gap between your synapses), effectively raising serotonin availability. These drugs have been found to be extraordinarily effective for treating major depressive disorders, and they are being investigated as a treatment for anxiety disorder, exemplifying the effect that serotonin has on mood. As selective serotonin reuptake inhibitors only affect one neurotransmitter, I think it is reasonable to conclude that serotonin has a pretty substantial role as a mood regulator.

Further evidence for serotonin’s role as a mood regulator comes from studies on genetics. One clinical investigation found that mutations in the genes which encode select serotonin receptors is a strong predictor for suicide; it is thought that said gene mutations may even double the risk of suicide[2]. Further studies have found that mutations in genes which influence the development of the serotonin system are strong predictors of depression, anxiety, seasonal affective disorder, aggression, panic attacks, and suicide[3].

Of course, this is to say nothing of the many mental illnesses thought to be affected by and in part caused by serotonin disruptions or abnormalities. Serotonin disturbances have been implicated in numerous mental illnesses, especially psychosis, impulse control disorders, and related mood disorders[4]. Monoamine neurotransmitters are thought by some to be the main drivers of conditions such as schizophrenia. While I could talk more about the incredibly exciting research going on in this area, I lack the expertise to talk about schizophrenia properly, and this article needs to focus on serotonin deficiencies!

Serotonin and cognition

According to the most current scientific literature, it is thought that serotonin has a significant and direct effect on cognitive function, particularly in the context of mental illnesses such as schizophrenia, as well as diseases like dementia or Alzheimer’s Disease. This shouldn’t be surprising, as we know that neurotransmitter levels typically affect cognitive performance in some way.

However, due to the ubiquitous nature of serotonin in the central nervous system, it seems that brain serotonin levels may affect almost every aspect of brain function.

The wide distribution of serotonin receptors throughout the brain makes it a very useful regulator for cognitive functions which require the simultaneous action and co-ordination of multiple different areas of the brain[5]. The varied distribution of serotonin receptors also means the neurotransmitter is intimately involved in most cognitive functions.

A literature published in a 2016 issue of Translational Neuroscience really drives home the fact that serotonin affects most aspects of brain function: clinical trials have found that serotonin influences memory, learning, spatial navigation, decision-making, social interactions, and attention[6].

Serotonin cognitive function

The reason serotonin activity is so influential on brain function is that it is highly prevalent in every area of the brain. Serotonin in the hippocampus helps control working memory and learning, while serotonin in the prefrontal cortex supports decision-making, social behavior moderation and relationship building. As serotonin helps with the co-ordination of activity in these areas of the brain, it is also heavily implicated in higher cognitive functions.

Interestingly, I found one clinical trial which suggests part of serotonin’s ability to enhance cognition comes from its interaction with other neurotransmitters, namely glutamate, GABA, dopamine, and acetylcholine[7]. It seems that serotonin may positively influence important brain chemicals, potentially fixing neurotransmitter imbalances, and thereby improving cognitive performance in a broad way. But this research is very new and more work needs to be done before I can embrace the idea that serotonin boosts the synthesis of other neurotransmitters!

Serotonin and digestion

As mentioned above, serotonin is also found in very high concentrations in the gastrointestinal tract. The enteric nervous system is an extensive network of nerves found suffused throughout the human gut. So extensive is this system of nerves that the enteric nervous system (ENS) is often referred to as the “second brain”; for context, the ENS has more neurons than a rat’s brain.

Serotonin is the neurotransmitter predominantly responsible for the contractions which move food through the gut. It is therefore no surprise to learn that serotonin deficiency is implicated in several disorders of the digestive system, and that when you raise serotonin levels, digestion tends to improve.

Researchers have found that serotonergic agents – substances which can raise serotonin levels – are efficacious in the treatment of irritable bowel syndrome, chronic diarrhea, and chronic constipation[8]. Considering how important your gut is for supporting mental health, cognitive performance and immunity, serotonin can be said to be intimately involved in lots of different aspects of health and performance.

Serotonin deficiency symptoms

What are the symptoms of low serotonin?

There are some very obvious symptoms of serotonin deficiency. While many of these symptoms can have other causes, it is worth exploring the possibility that you are suffering from a serotonin deficiency, particularly if the causes of low serotonin listed below apply to you!

Symptoms of low serotonin

Psychological symptoms of low serotonin

Here are the most common psychological/cognitive symptoms of low serotonin:

  • Anxiety
  • Panic
  • Low mood
  • Depression
  • Compulsive behaviors
  • Aggression
  • Low self-esteem
  • Poor memory function
  • Loss of motivation
  • Lack of focus

If you’re experiencing any of these symptoms, then it is really important that you talk to your doctor and explore the possibility that you have low serotonin.

Physical symptoms of low serotonin

Here are the most common physical signs that you have a serotonin deficiency:

  • Digestive problems
  • Insomnia
  • Sleep disturbances
  • Carbohydrate cravings
  • Compulsive eating
  • Fatigue
  • Nausea
  • Weight gain

Again, if you are struggling with any of these symptoms, it is vital that you talk to a medical professional as soon as possible to see if you have low serotonin.

Causes of low serotonin

So what causes low serotonin?

There are lots of things that can cause low serotonin. Some of them are acute causes of low serotonin; things that sap the amount of the neurotransmitter available in the brain. Other causes are more systemic, limiting your ability to produce more neurotransmitters.

Low serotonin causes

Common causes of serotonin deficiency include:

  1. Use of serotonergic drugs such as MDMA
  2. Lack of exercise
  3. Low sunlight exposure
  4. Low Vitamin D
  5. Lack of carbohydrates in diet
  6. Low Tryptophan intake
  7. Low omega 3 intake
  8. Having fewer serotonin receptors
  9. Having reduced serotonin synthesis capacity
  10. Chronic stress
  11. Acute anxiety

That’s quite a varied list of potential causes. Unfortunately, most people in the modern world suffer from at least one of these issues, and as such, are probably struggling with low serotonin.

The worrying rise in low carbohydrate diets and a rapid reduction in the amount of omega 3s people consume are potentially causing a systemic decline in serotonin levels at the population level. This is the problem of serotonin depletion.

Serotonin depletion

What is serotonin depletion?

Serotonin depletion, also called tryptophan depletion, is where your diet is systemically devoid of the nutrients you need to make serotonin. Specifically, a lack of tryptophan – the amino acid used to make serotonin – in your diet can cause a steady decline in your serotonin levels over many months and years.

Because the lack of tryptophan in your diet will inhibit the synthesis of new serotonin, you will not experience a rapid decline in serotonin levels; rather, you will experience a slow reduction in your serotonin levels. This is a slow decline rather than a rapid fall; as such, you will not experience intense symptoms of serotonin deficiency. You may not even realize you’re experiencing serotonin depletion; this is why it is so important to talk with a healthcare professional if you experience any symptoms of low serotonin.

How to increase serotonin levels

The most effective way to raise serotonin levels is to use SSRI antidepressants. If you are suffering with depression or severe anxiety, and low serotonin has been determined to be the cause, then you will likely be prescribed an SSRI antidepressant. However, if you have not been diagnosed with depression linked to low serotonin, and you have not been prescribed an SSRI by your healthcare provider, then you should not be using those drugs. Neurochemistry is extremely complicated and delicate; using drugs like SSRIs outside the supervision of doctors or psychotherapists will almost always cause serious long-term issues.

For those of you suffering with mild forms of depression, anxiety, or other negative emotions, then it is worth exploring some natural ways to raise serotonin.

Luckily, there are some very simple, cheap and effective ways to raise serotonin levels naturally.

How to naturally increase serotonin levels

The best way to treat low serotonin obviously differs person to person depending on the exact causes of the problem. But for most people, taking some simple steps can drastically improve serotonin production and receptor health, thus reducing low serotonin symptoms like depression and anxiety. This is because most cases of serotonin deficiency are caused by the same issues.

Get more exercise

Exercise is one of the most reliable and easy ways to stimulate the release of serotonin in the brain. Activities such as running, lifting weights, swimming, and even brisk walking have all been shown to acutely raise serotonin levels in the brain, thereby reducing anxiety and promoting a positive mood (and healthy digestion).

Eat foods high in tryptophan

Tryptophan is the raw building block of serotonin. Without tryptophan, you simply cannot make any serotonin. While there are lots of foods rich in this amino acid, many people still do not consume enough tryptophan on a daily basis to support optimal serotonin synthesis. If a tryptophan deficiency continues for a long time, serotonin depletion and serotonin deficiency will surely follow.

Foods high in tryptophan include: cheese, milk, eggs, peanuts, turkey, fish, pumpkin seeds, and chicken. I recommend upping your intake of peanuts, pumpkin seeds and cheese if you think you may have low serotonin caused by a tryptophan deficiency.

Get more sunlight (or use a lightbox)

Sunlight is as reliable a trigger for serotonin release as they come. We have long known that exposure to sunlight leads to higher blood serotonin levels; in some cases, people have reported that upping sunlight exposure (as a way to increase vitamin D) has helped reduce anxiety and depression symptoms as effectively as some antidepressant medications[9].

While low Vitamin D is correlated with low serotonin, it is not clear that this is the mechanism by which sunlight rapidly raises serum levels of the neurotransmitter. It is possible that the skin, as a major part of the serotonergic system, responds to sunlight in a way that directly triggers the release of serotonin. The skin is capable of producing the neurotransmitter, so this is a possibility warranting further study in my opinion.

Use serotonin supplements

Serotonin supplements can significantly improve serotonin synthesis, reduce serotonin reuptake, and help prevent serotonin depletion. There are lots of natural supplements which promote health blood serotonin levels. Of course, different substances work in different ways. But natural substances such as amino acids, vitamins, and herbal extracts can effective raise levels of serotonin.

I have already mentioned tryptophan and Vitamin D. Supplementing with both of these substances has been shown to raise serotonin levels in otherwise healthy people.

Serotonin supplements

Here is a list of supplements proven to raise serotonin availability in the blood and brain:

  • Vitamin D
  • Trypophan
  • 5-HTP
  • S-adenosyl-L-methionine (SAMe)
  • Vitamin B6
  • Zinc
  • Rhodiola rosea
  • Ashwagandha

The last two substances in this list are powerful anxiolytics, which means they reduce anxiety and stress. While they do not increase serotonin supply directly, they do help adult brain serotonin deficiency indirectly by reducing anxiety (and cortisol along with it).

The Vitamin B and Zinc are included in this list because deficiencies in both of these nutrients has been linked with anxiety, depression, lethargy, and poor sleep quality. On top of these supplements, people with disturbed sleep may want to consider adding in melatonin supplements to help fix their circadian rhythm. Poor sleep is tightly correlated with chronically low serotonin levels.

These treatments are not suitable for people with serious depression or severe neurotransmitter imbalances. If you are suffering from serious and systemic issues with your serotonin system, talk to your doctor about treatment options and medications. If you have a severe serotonin deficiency, neurotransmiter imbalance or hormone imbalance, then you will likely require antidepressants like selective serotonin reuptake inhibitors.

There are also specific nootropics designed to raise serotonin levels. It is worth checking out the best nootropics on the market today to see if any can help you by reducing stress and anxiety and improving cognitive performance.


[1] Knutson B, Wolkowitz OM, Cole SW, et al. Selective alteration of personality and social behavior by serotonergic intervention. Am J Psychiatry. 1998;155(3):373-379. doi:10.1176/ajp.155.3.373

[2] Ito Z, Aizawa I, Takeuchi M, Tabe M, Nakamura T (December 1975). “[Proceedings: Study of gastrointestinal motility using an extraluminal force transducer. 6. Observation of gastric and duodenal motility using synthetic motilin]”. Nihon Heikatsukin Gakkai Zasshi11 (4): 244–6.

[3] Albert PR, Benkelfat C. The neurobiology of depression–revisiting the serotonin hypothesis. II. Genetic, epigenetic and clinical studies. Philos Trans R Soc Lond B Biol Sci. 2013;368(1615):20120535. Published 2013 Feb 25. doi:10.1098/rstb.2012.0535

[4] Sumiyoshi T, Kunugi H, Nakagome K. Serotonin and dopamine receptors in motivational and cognitive disturbances of schizophrenia. Front Neurosci. 2014;8:395. Published 2014 Dec 4. doi:10.3389/fnins.2014.00395

[5] Serotonin Modulation of Prefronto-Hippocampal Rhythms in Health and Disease. Puig MV, Gener T. ACS Chem Neurosci. 2015 Jul 15; 6(7):1017-25.

[6] Švob Štrac D, Pivac N, Mück-Šeler D. The serotonergic system and cognitive function. Transl Neurosci. 2016;7(1):35-49. Published 2016 May 9. doi:10.1515/tnsci-2016-0007

[7] Seyedabadi M, Fakhfouri G, Ramezani V, Mehr SE, Rahimian R. The role of serotonin in memory: interactions with neurotransmitters and downstream signaling. Exp Brain Res. 2014;232(3):723-738. doi:10.1007/s00221-013-3818-4

[8] Camilleri, Michael Serotonin in the gastrointestinal tract, Current Opinion in Endocrinology, Diabetes and Obesity: February 2009 – Volume 16 – Issue 1 – p 53-59

[9] Penckofer S, Kouba J, Byrn M, Estwing Ferrans C: Vitamin D and depression: where is all the sunshine? Issues Ment Health Nurs 2010, 31:385–393.