Understanding serotonin and coffee
More people around the world drink coffee compared to any other drink, with about 98 million cups being consumed in the UK every day. Why is coffee so popular? For many people, drinking coffee improves mood - could coffee be linked to the “feel-good” chemical serotonin? Below, we dive deeper into the science of serotonin and coffee.
In short, coffee raises the amount of serotonin in the brain by stopping it from being broken down. This can cause a rare condition known as serotonin syndrome, which has symptoms such as confusion, agitation, shivering, and muscle twitching.
What is serotonin?
Serotonin is a messenger that carries information from one part of the body to another. It acts as both a neurotransmitter and a hormone. A neurotransmitter is a chemical that allows a message or signal to be sent from one nerve cell (neuron) to another. The first nerve cell releases the neurotransmitter into the space between neurones, and the neurotransmitter travels across the short distance to the second nerve cell. This means that neurotransmitters send messages over short distances in the body. In other words, they act locally.
A hormone is a messenger chemical produced by a gland and secreted into the bloodstream. Hormones travel through the bloodstream and send signals to their target organs. Since they travel through the bloodstream, hormones are able to reach and affect organs that are far away from the hormone’s own site of production. Unlike neurotransmitters, hormones act globally.
Both neurotransmitters and hormones affect a wide variety of physiological and psychological processes, including sleep, appetite, attention, and mood. Since serotonin acts as both a neurotransmitter and a hormone, it operates both locally and globally, sending messages to parts of the body that are both near and far.
Where is serotonin produced?
Nearly all of the serotonin in the body is made in the gut. Around 90% of the serotonin in the body is produced by the cells lining the digestive tract with help from microbes found in the gut.1 Microbes are microorganisms that are too small to be seen with the naked eye, such as bacteria and many types of fungi. In the gut, there are bacteria that do not harm the body or cause disease. These bacteria help the cells lining the digestive tract to produce serotonin.
A small amount of serotonin is produced in the brainstem. The brainstem is the part of the central nervous system through which the brain is connected to the spinal cord. Serotonin is also found in blood platelets.2 Platelets are components of blood that help wound healing by causing blood to clot.
So, serotonin is found in three different parts of the body: the digestive tract, the brainstem, and the platelets.
How does the body make serotonin?
Serotonin is made from the amino acid tryptophan. When we eat food containing tryptophan, it is absorbed by the body and used to synthesise serotonin.3 The rate at which serotonin is produced in the body depends on the amount of tryptophan present.4 Tryptophan is an essential amino acid, which means unlike other non-essential amino acids, the body cannot produce its own tryptophan4. Instead, it must rely on food sources, such as:
What does serotonin do?
Serotonin is an important chemical because it affects a wide range of physical and mental processes.
Serotonin affects mental health
Serotonin plays an important role in mood regulation. A higher level of serotonin improves mood while a decrease in serotonin results in a low mood.3 Low levels of serotonin are seen in depression, a mental illness in which people experience low mood and a lack of pleasure in things they used to enjoy. Many treatments for depression involve trying to increase the amount of serotonin in the brain.
A type of drug used to treat depression is selective serotonin reuptake inhibitors (SSRIs). Once serotonin has sent a message, it is normally taken up by nerve cells (serotonin reuptake). Selective serotonin reuptake inhibitors work by stopping the nerve cells from absorbing serotonin, which means that the amount of serotonin available in the brain increases. This helps to improve symptoms of depression like low mood. It is important to note, however, that not all patients with depression respond to SSRIs and that a combination of other treatment methods such as therapy, is usually recommended.
It is not only once depression has developed that serotonin can be helpful; it also helps to reduce susceptibility to depression. This means that in healthy people or those without depression, maintaining an adequately high level of serotonin can help protect against developing depression in the future. There are several ways of increasing serotonin in the body without using selective serotonin reuptake inhibitors or other medication.5
- Eating foods that are rich in tryptophan
- Spending time in bright light
- Engaging in physical exercise
So, serotonin affects our mental health, and can help in both the treatment and the prevention of depression.
Serotonin affects memory
Serotonin affects our memory and is important in helping us remember the things we learn. Scientists are still investigating the pathways through which serotonin affects memory.
Serotonin helps regulate energy balance
After a meal, serotonin promotes the breaking down of food in the gut and the absorption of nutrients into the bloodstream. It also reduces appetite, which helps to maintain nutrient and energy balance in the body.
Serotonin is important in wound healing
Serotonin is a vasoconstrictor; this means it causes the space inside blood vessels to become thinner. It also helps blood clots to form over cuts and wounds.
Serotonin influences the sexual drive
The role of serotonin in sexual drive is complex, however, there is scientific evidence that elevated levels of serotonin can negatively affect sexual performance. For example, one of the side effects of selective serotonin reuptake inhibitors (which increase serotonin in people with depression) is sexual dysfunction.6
Coffee is the most popular beverage in the world. Coffee beans are harvested from Arabica and Robusta trees, which grow in warm climates, and are used to make around 2 billion cups of coffee per day. Coffee contains a range of phytochemicals (substances produced by plants) that can affect health, the most well-known of which is caffeine.
Components of coffee
- Caffeine (a type of stimulant - stimulants are chemicals that speed up or “stimulate” brain activity)
- Tannins (a group of bitter chemicals produced by plants)
Effects of coffee (caffeine) on the body
Caffeine improves alertness and attention
Caffeine consumption has a positive effect on cognition. As a stimulant, it sharpens attention, increases alertness, and improves overall mental performance. However, caffeine is not a viable substitute for a good night’s sleep. Scientific research has found that the decline in cognitive performance because of sleep deprivation cannot be undone or nullified by drinking coffee.
Caffeine can help relieve pain
Painkillers such as paracetamol and ibuprofen can be made more effective by adding caffeine to them. 7 Caffeine provides a boost that helps with pain relief.
Caffeine reduces sleepiness
The effects of caffeine consumption on sleep differ from person to person, as people are more susceptible than others. However, in general, caffeine reduces sleepiness and can reduce the quality of sleep.7 It can also contribute to insomnia (difficulty falling asleep or staying asleep).
Caffeine can cause anxiety
Caffeine consumption can cause anxiety, especially in people who suffer from anxiety or other mood disorders 7. Drinking a larger amount of coffee makes experiencing anxiety more likely.
Caffeine increases blood pressure
After caffeine consumption, blood pressure temporarily increases, but this effect often diminishes over time. This is because the body develops a tolerance to (becomes used to) caffeine if it is consumed habitually.7
Caffeine affects digestion
Caffeine consumption causes the stomach to produce gastric acid, an important digestive chemical. Research also suggests that coffee can also disrupt the bacteria found in the gut.8
Having looked at the science of serotonin and coffee, we now shift our focus to the link between the two.
The link between serotonin and coffee
Is there a connection between serotonin and coffee? In this section, we look at what research says about coffee and explore whether, and how, it affects serotonin.
Coffee consumption raises serotonin
Drinking coffee can increase the amount of serotonin in the body as caffeine stops serotonin from being broken down. This depends on the amount of caffeine present in the type of coffee, as well as the degree to which the coffee beans are roasted.9 Roasting coffee reduces its ability to stop serotonin breakdown, and one scientific study found that green Robusta coffee is the most effective.9
Coffee can cause serotonin syndrome
Serotonin syndrome is a rare condition caused by elevated serotonin levels in the body. It usually occurs in people who are taking selective serotonin reuptake inhibitors, if they are also taking other substances that can increase serotonin, such as other antidepressant medications or coffee.
The symptoms of serotonin syndrome include:
- Mental confusion
- Muscle twitching or stiffness
- Increased heart rate (tachycardia)
Since coffee can increase the amount of serotonin in the body, it is recommended that people who are currently taking selective serotonin reuptake inhibitors monitor their coffee consumption.
Is coffee an antidepressant?
As caffeine helps to increase the level of serotonin in the brain, it has an antidepressant effect (it improves mood). However, drinking too much coffee can have a negative effect on mental health, and can cause depression and anxiety.
Does serotonin cause bowel movement?
Coffee consumption is known to stimulate bowel movement. However, this likely happens through a mechanism that is not related to serotonin. Coffee stimulates the production of gastric acid in the stomach, which helps to digest food and move it along the digestive tract.
Should I drink decaf coffee?
Decaffeinated coffee is made by removing caffeine from regular coffee. It is a convenient alternative for those who enjoy the taste of coffee but would like to avoid some of the negative effects of caffeine on the body. However, small amounts of caffeine are not bad for health, so the choice between caffeinated and decaffeinated coffee is a matter of personal choice.
Serotonin is a chemical that is synthesised in the body from the amino acid tryptophan and affects many mental and physical processes. Caffeine from coffee can increase the amount of serotonin by stopping it from being broken down, which can cause a condition known as serotonin syndrome. Therefore, moderate coffee consumption is recommended.
- Jones LA, Sun EW, Martin AM, Keating DJ. The ever-changing roles of serotonin. The International Journal of Biochemistry & Cell Biology [Internet]. 2020 Aug 1 [cited 2023 Jan 6];125:105776. Available from: https://www.sciencedirect.com/science/article/pii/S1357272520300935
- Maclean JA, Schoenwaelder SM. Chapter 5 - serotonin in platelets. In: Pilowsky PM, editor. Serotonin [Internet]. Boston: Academic Press; 2019 [cited 2023 Jan 6]. p. 91–119. Available from: https://www.sciencedirect.com/science/article/pii/B978012800050200005X
- Jenkins TA, Nguyen JCD, Polglaze KE, Bertrand PP. Influence of tryptophan and serotonin on mood and cognition with a possible role of the gut-brain axis. Nutrients [Internet]. 2016 Jan 20 [cited 2023 Jan 6];8(1):56. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728667/
- Richard DM, Dawes MA, Mathias CW, Acheson A, Hill-Kapturczak N, Dougherty DM. L-tryptophan: basic metabolic functions, behavioral research and therapeutic indications. Int J Tryptophan Res [Internet]. 2009 Mar 23 [cited 2023 Jan 6];2:45–60. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908021/
- Young SN. How to increase serotonin in the human brain without drugs. J Psychiatry Neurosci [Internet]. 2007 Nov [cited 2023 Jan 6];32(6):394–9. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2077351/
- Jing E, Straw-Wilson K. Sexual dysfunction in selective serotonin reuptake inhibitors (Ssris) and potential solutions: A narrative literature review. Ment Health Clin [Internet]. 2016 Jun 29 [cited 2023 Jan 7];6(4):191–6. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007725/
- van Dam RM, Hu FB, Willett WC. Coffee, caffeine, and health. Campion EW, editor. N Engl J Med [Internet]. 2020 Jul 23 [cited 2023 Jan 7];383(4):369–78. Available from: http://www.nejm.org/doi/10.1056/NEJMra1816604
- Rodak K, Kokot I, Kratz EM. Caffeine as a factor influencing the functioning of the human body—friend or foe? Nutrients [Internet]. 2021 Sep [cited 2023 Jan 7];13(9):3088. Available from: https://www.mdpi.com/2072-6643/13/9/3088
- Grzelczyk J, Budryn G, Peña-García J, Szwajgier D, Gałązka-Czarnecka I, Oracz J, et al. Evaluation of the inhibition of monoamine oxidase A by bioactive coffee compounds protecting serotonin degradation. Food Chemistry [Internet]. 2021 Jun 30 [cited 2023 Jan 7];348:129108. Available from: https://www.sciencedirect.com/science/article/pii/S0308814621001102