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Mental health awareness: what is serotonin?


What is serotonin? As we most likely already know, our mental health is just as important as our physical health – this is something many of us have perhaps realised especially over the course of the global Covid-19 pandemic. Serotonin affects important factors of our well-being, such as our mood, the quality of our sleep, our energy levels and our digestive system.

When the body is bursting with serotonin, we tend to smile more, feel more at peace and fall asleep more easily. When people suffer from depression, they feel these effects only to a small degree: depressed people have serotonin levels that are 50 per cent lower than healthy people. This finding gave rise to the hypothesis that a serotonin deficiency causes depression.

So, why is serotonin more than just a happiness hormone? Which symptoms arise with a serotonin deficiency, and can you can best optimise your serotonin level by natural means? All will be revealed in our latest article on serotonin.

What is serotonin?

happy young people laughing on a beach

First things first, serotonin is known as the happiness hormone, taking on the function of a hormone and a neurotransmitter. Tryptophan, an amino acid in food, serves as a precursor of serotonin. Astonishingly, 95 per cent of our serotonin is produced in our gut, while the rest is produced in the brain. From serotonin, the body in turn forms the sleep hormone melatonin.[1]

What are neurotransmitters? These messenger substances transmit information from one nerve cell to the next. For example, neurotransmitters in the muscles cause muscle fibres to contract and relax.

What is the blood–barrier and why is it important?

Substances that want to enter the nervous system from the bloodstream must pass through the blood–brain barrier. However, not just any substance can do this. Transport proteins are based around this barrier and only allow certain substances to enter. Serotonin from the blood is denied entry. Only its precursor tryptophan can cross it.

Enzymes and nutrients ultimately convert the amino acid tryptophan into the happiness hormone serotonin. If there is a lack of vitamin B6, vitamin D, omega-3 fatty acids or magnesium, this conversion into serotonin can only occur to a limited extent.[1–3]

Did you know that bacteria produce serotonin? In 2015, the California Institute of Technology was able to determine in mice that without gut flora, much less serotonin is produced. Researchers are now transferring this knowledge to humans. Healthy gut flora not only improves digestion but also your mood.[4, 5]

How does serotonin work?

Serotonin puts you in a good mood, gives you restful sleep and increases your drive. It not only affects your psyche, but it also regulates body temperature and supports digestion. As a neurotransmitter, it transmits stimuli that cause the heart to beat, muscles to move and thought processes to take place. In addition, serotonin ensures that anaemia does not occur, as in the case of an iron deficiency.[1, 6]

Serotonin is called the happy hormone because it has a mood-boosting effect. It inhibits the area in our brain called the cerebrum, which causes negative emotions. Together with the neurotransmitter dopamine, it drives away negative feelings such as fear, sadness and depression.[7]

Our heart also benefits from serotonin each time it beats, as the hormone helps keep blood pressure under control. As is widely known, high blood pressure is considered a precursor to numerous cardiovascular diseases such as heart attacks, hardening of the arteries and strokes.[8]

Serotonin deficiency

If the level of the happiness hormone drops, it’s easy to assume that it’s mainly our sense of happiness that suffers. But symptoms of serotonin deficiency can be recognised all over our body.

What causes low levels of serotonin?

Researchers have not yet been able to find out exactly what triggers serotonin deficiency. They suspect the following causes have a part to play:[3, 9]

  • Insufficient serotonin receptors
  • Defective serotonin receptors due to drug abuse
  • Deficiencies in nutrients such as vitamin D, vitamin B6, magnesium, omega-3 fatty acids and tryptophan

Researchers in one study that investigated childhood trauma concluded that traumatic experiences may have lowered the serotonin levels of the people studied over the years.[10]

When serotonin receptors don’t work properly

Specific receptors for each chemical compound are found on the surface of cells. As soon as a substance docks onto its respective receptor, reactions are set in motion in the cell. If there is a deficit of receptors for serotonin, the happiness hormone cannot function properly – causing a deficiency. Damage to the receptors – for example, through drug abuse – can cause serotonin deficiency.[11–13]

Serotonin and nutrients

Vitamin B6 and serotonin: Studies have shown in people with depression who have low serotonin levels that vitamin B6 enables the conversion of tryptophan into serotonin. Therefore, people with a serotonin deficiency should make sure they have enough vitamin B6. Foods particularly rich in B6 include legumes, whole-grain products and green vegetables.[2, 14]

Vitamin D and serotonin: During wintertime, the body’s own vitamin D production is weakened due to low sunlight. Now your body also converts less tryptophan into serotonin. Ergo, serotonin levels can drop in winter without vitamin D supplementation [13].

Omega-3 fatty acids and serotonin: Omega-3 fatty acids are also linked to serotonin. Researchers found that low omega-3 levels also leads to reduced serotonin levels.[13] Omega 3 is found in large quantities in cold-water fish such as salmon, mackerel and herring, for example.

Serotonin deficiency symptoms

Serotonin has the greatest influence on your mood, but a deficiency is also associated with a number of physical complaints in addition to psychological symptoms.[7]

Psychological symptoms

Physical symptoms

Depressive moods

Increased craving for carbohydrates

Concentration problems

Weight gain

Mood swings, aggressiveness, anxiety


Attention deficit disorder

Gastrointestinal complaints

Decreased self-confidence and libido

General food cravings

Serotonin syndrome

Active substances – such as LSD, cocaine, high doses of tryptophan and antidepressants, in addition to tumours – can cause serotonin levels to skyrocket, which can lead to serotonin syndrome. High levels of serotonin overload the receptors, leading to the following physical symptoms.

  • Fever, tremors
  • Nausea, vomiting
  • Decreased performance
  • Anxiety, restlessness, disorientation

The symptoms usually disappear when those affected stop taking certain medication. Never stop taking antidepressants without consulting your doctor – these drugs usually have to be phased out gradually.[15]

Serotonin and depression

Depression is not simply a short-term phase of grief or despair. It is a serious illness that requires intensive therapy. Not only the psyche, but the entire body suffers from the consequences of depression.

What is depression? Depression is a mental illness that has an immense impact on mood. People with depression suffer from severe lack of interest and struggle with negative thoughts. Depression can be caused by emotionally stressful life events or brain metabolism disorders.[16]

Does a serotonin deficiency lead to depression?

serotonin deficiency doesn't lead to depression

People with depression have a 50 per cent lower hormone level. In the 1960s  low serotonin levels were said to be associated with the occurrence of depression. Nowadays, scientists are questioning this statement. Although  serotonin metabolism in the brain is disturbed in cases of depression, the following question remains: does serotonin deficiency lead to depression or does depression lead to a serotonin deficiency?[13, 17–20]

Researchers have conducted numerous studies to find out whether serotonin deficiency causes depression. Studies have tried to lower serotonin levels with a diet low in tryptophan in order to induce depression in the test participants. The level did drop, but this did not lead to depression or depressive symptoms. When people with depression were given serotonin as a medication, researchers observed only minimal improvement. Other studies show that too little tryptophan reaches the brains of people with depression. [13, 17-20]

Research has thus not been able to prove that a serotonin deficiency leads to depression, as has been assumed for years. Serotonin seems to play an important role in depression, but it is only a small piece of the puzzle.

What are antidepressants?

Antidepressants belong to the group of psychotropic drugs, the drugs used to treat mental illness. They influence brain metabolism by affecting messenger substances such as serotonin.[21]

How do serotonin reuptake inhibitors work?

Among the antidepressants doctors prescribe are serotonin reuptake inhibitors (SSRIs). They act like a filter in the central nervous system. When serotonin as a neurotransmitter transmits stimuli, it passes from one nerve cell to the next and is used up. SSRIs block serotonin from exiting the cell, whereupon other neurotransmitters take over stimulus transmission.

This way, enough serotonin remains in the brain and can carry out its mood-lifting function. SSRIs are used to treat mild to moderate depression. As with other antidepressants, a noticeable effect on mood only becomes apparent after several weeks. During this time, serotonin syndrome can develop as a side effect – that is, an excess of serotonin.[21]

According to a Swiss study, the intensity of dreams decreases with SSRIs. Those affected can also remember less easily what they have dreamed.[22]

A doctor usually determines the severity of depression through a conversation in person and a physical examination. How long an antidepressant has to be taken for is decided after regular check-ups. Depending on whether symptoms improve, the dose can be reduced. Common side effects of antidepressants are a decrease in libido, headaches, restlessness and nausea.[21]

According to several studies on nutrition and depression, an adequate supply of omega-3 fatty acids – including in the form of omega-3 supplements – and tryptophan can improve the effect of antidepressants.[23]

Treatment: boost serotonin levels

Our food also contributes to the production of the happiness hormone serotonin. But for the body to be able to draw serotonin from our food, it needs important nutrients, exercise and light.

Food makes us happy – this is not groundbreaking news for many. A juicy steak, our favourite chocolate or a colourful fruit salad give us that simple pleasure. Just the sight of it triggers happiness in us. When we indulge in our favourite foods, numerous psychological and neurobiological processes take place, and the serotonin hormone plays an important role.

You should incorporate plenty of the amino acid tryptophan into your diet, so that your body can create the mood-booster serotonin. You can increase your tryptophan levels with the following foods:[24]


Tryptophan content in mg/100 g

Parmesan (37% fat)


Soy flour 


Emmental cheese (45% fat)


Cashew nuts


Wheat germ






Chicken eggs


Porcini mushroom


Cereals, grain


Daily tryptophan intake and 5-HTP

The International Journal of Tryptophan Research recommends a daily tryptophan intake of 250 to 450 milligrammes. You can meet this requirement with just two cheese sandwiches! According to the journal, a person takes in an average of up to 1,000 milligrammes of tryptophan a day through their diet.[25]

5-Hydroxytryptophan, also known as 5-HTP or a form of tryptophan, is a supplement commonly used to boost serotonin production. 5-HTP originates from the seeds of an African shrub named Griffonia Simplicifolia.

Unlike other forms of tryptophan, 5-HTP isn’t present in any food. It can only be added to our bodies by taking a supplement.

How do I boost serotonin levels?

Tips on how to boost serotonin levels

Eating plenty of tryptophan-rich foods is not the only way to boost serotonin levels. Some nutrients prevent tryptophan from crossing the blood–brain barrier or being converted into serotonin. These include amino acids, caffeine and nicotine.

Only a limited number of amino acids can reach the nervous system and pass the blood–brain barrier. Such competition can prevent tryptophan from also passing the barrier. Therefore, if you have a serotonin deficiency, you should make meals relatively low in protein with tryptophan-rich foods.[13]

It’s no revelation that sports and sunshine stimulate serotonin production. Other factors that boost serotonin levels include:[13, 14, 26-28]

  • Sugar
  • Vitamin D
  • Vitamin B6
  • Magnesium
  • Omega-3 fatty acids

Sugar molecules are great for tryptophan. When you eat sugar, your pancreas makes insulin. This hormone facilitates the entry of tryptophan into the central nervous system.[13]

Did you know that if serotonin levels in the brain drops, your craving for sweets increases? The brain tells you that it needs sugar, so it can transport tryptophan into the brain.[13]

woman working out

Test for serotonin deficiency

A serotonin test can determine the serotonin concentration in your urine. The amount of serotonin is measured in microgrammes per gramme of creatinine. Depending on the reading of the urine test, you can determine whether your serotonin levels are within a healthy range.

Keep in mind that hormones are subject to natural fluctuations during the day. For example, there may be sporadic high or low levels. If they are in a very low or very high range, you should investigate the possible causes with a doctor!



< 60 µg/g creatinine

Insufficient supply

60-450 µg/g creatinine

Optimal supply

> 450 µg/g creatinine

Excessive supply

An analysis of your amino acids could also prove useful in providing more insights into your tryptophan levels. These days, you can perform an amino acid home test by collecting a blood sample discreetly and painlessly in the comfort of your own home. 

The serotonin hormone – at a glance

What is serotonin?

Serotonin functions as a hormone and as a neurotransmitter – that is, as a messenger substance in the brain. It is formed from the amino acid tryptophan, which has to cross the blood–brain barrier to do so.

Why do I need serotonin?

Serotonin makes us feel happy. The hormone also controls blood pressure and regulates our sleeping pattern.

What causes serotonin deficiency?

A diet low in tryptophan, a lack of receptors and insufficient levels of vitamin D, B6, magnesium and omega-3 fatty acids can lead to serotonin deficiency. If you lack serotonin, you will feel low and hungrier, and you will suffer from mood swings.

Is serotonin related to depression?

People with depression have low serotonin levels. However, it has not been proven that a lack of serotonin leads to depression.

How can I boost serotonin levels?

Eating tryptophan-rich foods along with carbohydrates can increase your serotonin levels. If your levels are low, you should eat a relatively low-protein diet and avoid nicotine and caffeine. Sports, sunshine and healthy gut flora stimulate serotonin production.


[1]        Pubchem, „Serotonin“. [Online]. Verfügbar unter: https://pubchem.ncbi.nlm.nih.gov/compound/5202. [Zugegriffen: 04-Juli-2018].

[2]        A.-M. Hvas, S. Juul, P. Bech, und E. Nexø, „Vitamin B6 level is associated with symptoms of depression“, Psychother. Psychosom., Bd. 73, Nr. 6, S. 340–343, Dez. 2004, doi: 10.1159/000080386.

[3]        R. P. Patrick und B. N. Ames, „Vitamin D hormone regulates serotonin synthesis. Part 1: relevance for autism“, FASEB J. Off. Publ. Fed. Am. Soc. Exp. Biol., Bd. 28, Nr. 6, S. 2398–2413, Juni 2014, doi: 10.1096/fj.13-246546.

[4]        „Microbes Help Produce Serotonin in Gut | Caltech“, The California Institute of Technology. [Online]. Verfügbar unter: http://www.caltech.edu/news/microbes-help-produce-serotonin-gut-46495. [Zugegriffen: 04-Sep-2018].

[5]        T. A. Jenkins, J. C. D. Nguyen, K. E. Polglaze, und P. P. Bertrand, „Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis“, Nutrients, Bd. 8, Nr. 1, Jan. 2016, doi: 10.3390/nu8010056.

[6]        Faller, Adolf; Schünke, Michael, Der Körper des Menschen - Einführung in Bau und Funktion, 16. Thieme.

[7]        D. DFARHUD, M. MALMIR, und M. KHANAHMADI, „Happiness & Health: The Biological Factors- Systematic Review Article“, Iran. J. Public Health, Bd. 43, Nr. 11, S. 1468–1477, Nov. 2014.

[8]        S. W. Watts, S. F. Morrison, R. P. Davis, und S. M. Barman, „Serotonin and Blood Pressure Regulation“, Pharmacol. Rev., Bd. 64, Nr. 2, S. 359–388, Apr. 2012, doi: 10.1124/pr.111.004697.

[9]        R. P. Patrick und B. N. Ames, „Vitamin D and the omega-3 fatty acids control serotonin synthesis and action, part 2: relevance for ADHD, bipolar disorder, schizophrenia, and impulsive behavior“, FASEB J., Bd. 29, Nr. 6, S. 2207–2222, Feb. 2015, doi: 10.1096/fj.14-268342.

[10]      J. M. Miller, E. L. Kinnally, R. T. Ogden, M. A. Oquendo, J. J. Mann, und R. V. Parsey, „Reported childhood abuse is associated with low serotonin transporter binding in vivo in major depressive disorder“, Synapse, Bd. 63, Nr. 7, S. 565–573, doi: 10.1002/syn.20637.

[11]      „Pschyrembel Online | serotonin“. [Online]. Verfügbar unter: https://www.pschyrembel.de/serotonin/K0KU3/doc/. [Zugegriffen: 04-Juli-2018].

[12]      „Study suggests ecstasy can damage serotonin receptors in the prefrontal cortex“, PsyPost, 03-März-2016. [Online]. Verfügbar unter: https://www.psypost.org/2016/03/study-suggests-ecstasy-can-damage-serotonin-receptors-prefrontal-cortex-41420. [Zugegriffen: 04-Juli-2018].

[13]      Donner, S., „Serotonin: Zum Glück gibt´s was zum Essen“, Vereine für Unabhängige Gesundheitsberatung (UGB). [Online]. Verfügbar unter: https://www.ugb.de/serotonin/serotonin-schokolade-fischoel-kohlenhydrate/. [Zugegriffen: 04-Juli-2018].

[14]      C. S. Paulose, K. Dakshinamurti, S. Packer, und N. L. Stephens, „Sympathetic stimulation and hypertension in the pyridoxine-deficient adult rat“, Hypertension, Bd. 11, Nr. 4, S. 387–391, Apr. 1988, doi: 10.1161/01.HYP.11.4.387.

[15]      „Pschyrembel Online | Serotoninsyndrom“. [Online]. Verfügbar unter: https://www.pschyrembel.de/Serotoninsyndrom/K0KU6/doc/. [Zugegriffen: 04-Sep-2018].

[16]      „Pschyrembel Online | Depression“. [Online]. Verfügbar unter: https://www.pschyrembel.de/Depression/K05PP/doc/. [Zugegriffen: 04-Sep-2018].

[17]      „Depression: Infos und Hilfe - Stiftung Deutsche Depressionshilfe“. [Online]. Verfügbar unter: https://www.deutsche-depressionshilfe.de/depression-infos-und-hilfe. [Zugegriffen: 04-Juli-2018].

[18]      K. Shaw, J. Turner, und C. Del Mar, „Are tryptophan and 5-hydroxytryptophan effective treatments for depression? A meta-analysis“, Aust. N. Z. J. Psychiatry, Bd. 36, Nr. 4, S. 488–491, Aug. 2002, doi: 10.1046/j.1440-1614.2002.01046.x.

[19]      P. L. Delgado u. a., „Serotonin and the neurobiology of depression. Effects of tryptophan depletion in drug-free depressed patients“, Arch. Gen. Psychiatry, Bd. 51, Nr. 11, S. 865–874, Nov. 1994.

[20]      J. R. Lacasse und J. Leo, „Serotonin and Depression: A Disconnect between the Advertisements and the Scientific Literature“, PLoS Med., Bd. 2, Nr. 12, Dez. 2005, doi: 10.1371/journal.pmed.0020392.

[21]      PatientenLeitlinie zur Nationalen Versorgungsleitlinie, Unipolare Depression, 2. Aufl. .

[22]      E. F. Pace-Schott, „Serotonin and dreaming“, in Serotonin and Sleep: Molecular, Functional and Clinical Aspects, Birkhäuser Basel, 2008, S. 307–324.

[23]      Birgit Holler B.sc., Manuela Konrad, „Depression – Ernährung als Therapie?“ 2010.

[24]      Lebensmitteltabelle für die Praxis; Der kleine Souci-Fachmann-Kraut, 5. Aufl. Wissenschaftliche Verlagsgesellschaft Stuttgart, 2011.

[25]      D. M. Richard, M. A. Dawes, C. W. Mathias, A. Acheson, N. Hill-Kapturczak, und D. M. Dougherty, „L-Tryptophan: Basic Metabolic Functions, Behavioral Research and Therapeutic Indications“, Int. J. Tryptophan Res. IJTR, Bd. 2, S. 45–60, März 2009.

[26]      B. V. Lim u. a., „Caffeine inhibits exercise-induced increase in tryptophan hydroxylase expression in dorsal and median raphe of Sprague-Dawley rats“, Neurosci. Lett., Bd. 308, Nr. 1, S. 25–28, Juli 2001.

[27]      P. Salmon, „Effects of physical exercise on anxiety, depression, and sensitivity to stress: a unifying theory“, Clin. Psychol. Rev., Bd. 21, Nr. 1, S. 33–61, Feb. 2001.

[28]      R. A. Sansone und L. A. Sansone, „Sunshine, Serotonin, and Skin: A Partial Explanation for Seasonal Patterns in Psychopathology?“, Innov. Clin. Neurosci., Bd. 10, Nr. 7–8, S. 20–24, 2013.

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