In this article, we’ll delve into the role of serotonin, how to increase serotonin naturally, and whether you can have too much serotonin.
What is serotonin?
Serotonin is a neurotransmitter – a type of hormone known for its effect on mood. In fact, serotonin is considered a natural mood stabiliser when functioning as it should.
But its role extends way beyond mood. Serotonin helps to regulate the function of major organs, including the heart, liver and kidneys.
Where is serotonin produced?
Serotonin is produced in different places in the body.
Most serotonin is produced by cells that line the gut wall – called enteroendocrine cells. While some serotonin stays and has effects in the gut, most serotonin passes through the gut wall where it is taken up, stored, and released by platelets that act as ‘transporters’ circulating in your bloodstream.
It’s thought that this serotonin is mainly responsible for activities involving major organs, such as heart rate, breathing rate, bladder control, and gut motility.
A small amount of serotonin is produced by cells in the brain and spinal cord – called neurons. This serotonin is thought to mainly regulate emotions and feelings.
Both ‘types’ of serotonin are the same – they are just produced in different places and by different cells. Saying that, gut-based serotonin cannot enter the brain because it can’t cross the blood brain barrier.
While scientists are still trying to figure out how gut-based serotonin might affect the brain, emerging studies in mice have shown that increased serotonin in the gut can influence the expression of serotonin receptors in the brain. For a deeper dive, check out this article on the gut-brain connection.
Certain gut microbes are capable of directly producing serotonin or indirectly producing serotonin by converting tryptophan - an essential amino acid - in foods to serotonin or through the production of compounds such as short-chain fatty acids (SCFAs) which can stimulate serotonin release from enteroendocrine cells.
Can you increase serotonin naturally?
- Physical activity can trigger an increase in tryptophan levels and serotonin production in the brain.
- Exposure to sunlight can help to regulate your body clock and cue your brain to produce serotonin.
- Spa therapies (e.g. massage, hydrotherapy) might increase serotonin levels alongside decreases in stress hormones, such as cortisol.
What about food?
Tryptophan is called an essential amino acid because the body can’t make it – it must be obtained from your diet.
Tryptophan helps to make serotonin, but not all the tryptophan you get from food will enter the brain from the bloodstream. For example, tryptophan is in competition with many other amino acids, so eating a very small amount of protein can limit the amount getting through to the brain. Not only that but there are many building blocks of serotonin including other vitamins and minerals such as vitamin D, B6 and omega 3 fatty acids. These need to be present to make serotonin too.
To support your mood, research points to a Mediterranean-style diet which emphasises plant-based foods, lean protein sources, and healthy fats. In fact, the SMILES trial showed that following this dietary pattern can improve mental health.
Table 1 shows what is typically included in a Mediterranean-style diet (The Mediterranean Diet Foundation 2011).
Serotonin and mental health
Changes in serotonin activity is linked with mental health conditions, such as depression. Treatment often includes the use of anti-depressants.
Almost all anti-depressants influence the brain’s serotonin system – common ones include selective serotonin reuptake inhibitors (SSRIs).
SSRIs work by blocking the re-absorption of serotonin into neurons which makes more serotonin available. This changes the activity of neurons in the brain, allowing signals to be transmitted more effectively.
Some antidepressants have effects on other neurotransmitters too – such as dopamine.
What is serotonin syndrome
Serotonin syndrome (also known as serotonin toxicity) is an uncommon but potentially serious reaction caused by certain medications, such as SSRIs. Serotonin syndrome happens when there is too much serotonin in your brain. It can happen when you increase the medication dose or start taking a new medication.
Symptoms are highly variable and range in severity - includes nausea and vomiting, diarrhoea, rapid heart rate and blood pressure, confusion, restlessness and agitation.
If you experience these symptoms, it’s important to seek immediate advice from your GP.
Summary
Serotonin has many roles in the body but is probably most well-known for its effects on mood.
There are many factors that can influence serotonin levels including physical activity and exposure to natural light. Anti-depressants can also influence serotonin levels by acting on the brain’s serotonin system.
A Mediterranean-style diet is linked with improvements in mood. Try and prioritise plant-based foods such as wholegrains, legumes, fruit and vegetables, lean protein sources such as fish and chicken, and healthy fats such as nuts, seeds, and olive oil.
Sources
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Gut bacteria and neurotransmitters. Microorganisms. (2022). Link.
Fifty years on: Serotonin and depression. Journal of Psychopharmacology. (2023). Link.
Human-derived bifidobacterium dentium modulates the mammalian serotonergic system and gut–brain axis. Cellular and Molecular Gastroenterology and Hepatology. (2020). Link.
Mediterranean diet pyramid today. Science and cultural updates. Public Health Nutrition. (2011). Link.
Possible role of exercise therapy on depression: Effector neurotransmitters as key players. Behavioural Brain Research. (2024). Link.
Serotonin-its synthesis and roles in the healthy and the critically ill. International Journal of Molecular Sciences. (2021). Link.
Spa therapy and peripheral serotonin and dopamine function: a systematic review. International Journal of Biometeorology. (2023). Link.
Summer and SERT: Effect of daily sunshine hours on SLC6A4 promoter methylation in seasonal affective disorder. The World Journal of Biological Psychiatry. (2025). Link.
The correlation between gut microbiota and both neurotransmitters and mental disorders: A narrative review. Medicine. (2023). Link.
The blood–brain barrier. Cold Spring Harbor Perspectives in Biology. (2015). Link.
