Serotonin, often referred to as the "happy chemical," is more complex than its popular image may suggest. This potent signalling molecule acts as both a neurotransmitter and a hormone, sending nerve impulses in the brain and influencing various bodily functions such as appetite and immunity.
Serotonin’s effects depend on how much the body produces and how certain cells respond to it, experts say. Below, we take a closer look at serotonin’s complexities—and what they might mean for your health.
What is serotonin?
In a nutshell, serotonin is a multipurpose chemical in the body which is classified as a neurotransmitter and hormone, says Dr. Troy Russell, MD. This means it sends signals between nerve cells and also acts as a regulatory agent in the blood.
Despite its storied reputation as a “brain chemical,” only a small amount of serotonin is actually produced in our grey matter. The majority is produced in the gut from the dietary amino acid tryptophan.
Serotonin function
Serotonin has many roles in the body, depending on which of its 15 different receptors it interacts with. Enzymes and transport proteins also influence serotonin's function, leading to its varied effects. For instance:
- Sleep: Serotonin helps regulate sleep by promoting the production of brain neurochemicals that induce tiredness. It also plays a role in maintaining normal breathing during sleep, with disruptions potentially contributing to conditions like sleep apnea.
- Cognition and memory: Animal studies suggest serotonin influences learning and behavioural adaptation by enhancing neural connections. Low levels of serotonin may coincide with attention difficulties and symptoms of attention deficit hyperactivity disorder (ADHD). In small studies of human volunteers, dysfunction within the serotonin system has been linked with dementia and mild cognitive impairment.
- Pain perception: Serotonin can both inhibit pain signals and perpetuate them, animal research suggests, depending on which serotonin receptors are occupied. Many prescription headache medicines work in part by stimulating specific serotonin receptors in the brain.
- Sexual function: While findings in rodents suggest brain serotonin may influence sexual behaviours, its effects in humans remain less clear. In humans, sexual dysfunction is a commonly reported side effect of medications that increase serotonin activity in the brain.
- Appetite and weight: Serotonin's role in metabolism and appetite regulation is intricate. Research in animals indicates it can stimulate the production of neurotransmitters that suppress appetite, yet elevated gut serotonin levels are associated with increased body mass.
- Immunity: Nearly all immune cells possess serotonin receptors or enzymes involved in serotonin metabolism. Research shows serotonin may influence conditions like gut inflammation, allergic asthma, and rheumatoid arthritis.
- Gut health and digestion: Elevated blood serotonin levels are linked to chronic diarrhoea, while low levels may contribute to constipation. Intestinal serotonin may also work closely with specific gut bacteria to coordinate fat metabolism.
Symptoms of low serotonin
The phrase “low serotonin” could describe one of several scenarios, says New York-based Dr. Diana Samuel, MD, an assistant professor of clinical psychiatry. One scenario is that the body isn’t producing enough serotonin to meet its needs; other possibilities are that some neurons don’t have enough serotonin receptors, or that receptors aren’t adequately grabbing onto serotonin.
Low serotonin can also mean that the chemical is breaking down too quickly to do its job. Low levels of serotonin affect people in different ways, Dr. Samuel says. Some people may experience increased impulsive aggression or suicidal behaviour, she says. Researchers have also observed carb cravings—possibly because carbohydrates are needed to facilitate serotonin synthesis.
Can I increase my serotonin levels?
Before exploring ways to increase your serotonin levels, it’s important to speak with your doctor about whether you’d benefit from a boost to begin with. Even among people who are experiencing signs of low serotonin, a different condition or an additional underlying cause could be involved—and amping up serotonin isn’t always better or safe.
Excess serotonin in the body can lead to a potentially life-threatening condition known as serotonin syndrome (or serotonin toxicity), marked by seizures, delusions, and spikes in heart rate.
Given serotonin’s importance in the body and the risks of elevated serotonin, medical guidance is key to ensure you’re taking steps that support—and not undermine—your health.
Foods that support healthy serotonin function
Tryptophan is an essential amino acid which can’t be made naturally in the body, which means that we have to get tryptophan through our diet. Protein is a natural source of tryptophan and other amino acids. The body converts tryptophan from food into 5-hydroxytryptophan (5-HTP) and then into serotonin. The World Health Organization recommends a daily tryptophan intake of 4 mg/kg of body weight—for a person weighing 68 kilograms, that’s about 272 mg of tryptophan a day.
Foods containing high concentrations of tryptophan include:
- Seeds and nuts, particularly pumpkin, chia, and sesame seeds
- Eggs
- Meat, poultry, and fish
- Soy products including tofu, soy beans, and soy milk
- Cheese, especially Parmesan, cheddar, and mozzarella
- Oats
- Lentils and beans
Lifestyle measures that may increase serotonin
Research suggests that certain behaviours can affect levels of serotonin. These include:
- Maintaining a sleep routine. Poor sleep can make you feel worse, and serotonin may play a role in this. Animal studies show that chronic sleep deprivation can desensitise some serotonin receptors in the brain, potentially leading to depressive symptoms. Fortunately, many people can improve their sleep by establishing a healthy, consistent bedtime routine or seeking guidance from a doctor.
- Exercising. During aerobic exercise, muscles may use amino acids that typically compete with tryptophan for access to the brain. This could increase the amount of tryptophan available for serotonin production, according to animal research. Government guidelines suggest 2.5 to 5 hours of moderate-intensity physical activity per week for overall health.
- Getting regular massages. Massages can do more than soothe muscles. A 2004 study found that pregnant women who received a 20-minute massage twice a week experienced increased serotonin levels and reduced stress hormones. Other studies on migraine sufferers suggest that massages can boost serotonin and alleviate headache symptoms.
- Connecting with others. Spending time with loved ones can also raise serotonin levels. Reflecting on happy memories may have a similar effect. This could explain why gratitude exercises, like "three good things," can improve mood.
Nutritional supplements that may increase serotonin
In Australia and many other countries, tryptophan supplements are restricted. Low dose tryptophan supplements are available over the counter in pharmacies. Higher dose tablets can only be obtained with a doctor’s prescription.
Serotonin and depression
At some point in life, many people may experience symptoms of depression. These can include a lack of motivation, loss of interest in activities once enjoyed, insomnia or sleeping too much, ongoing fatigue, restlessness, feelings of worthlessness, trouble concentrating, and recurring thoughts of death. For years, researchers have suspected a link between serotonin dysfunction and depression. A 2016 meta-analysis of 10 molecular-imaging studies in humans found a correlation between depression and low serotonin-receptor binding in certain parts of the brain.
That said, depression is a complex illness likely shaped by genetic, psychological, environmental, and other factors, public health experts say. If you are experiencing signs of depression, speak with your doctor to develop a comprehensive care plan.
Selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressant class in Australia. They work by slowing the removal of serotonin from between neurons, thereby increasing the availability of serotonin in the brain.
What is serotonin syndrome?
Serotonin syndrome is a rare but potentially life-threatening side effect of excessive serotonin in the body. Most cases occur when two or more serotonin-elevating medicines or drugs are taken at the same time, Dr. Samuel explains.
Symptoms of serotonin syndrome
Serotonin syndrome is marked by major changes in mental status, neuromuscular functioning, and autonomic functioning, Dr. Samuel says. Symptoms can present themselves in minutes to hours and may include:
- Agitation
- Confusion or disorientation
- Overactive startle response
- Dilated pupils
- Elevated heart rate and body temperature
- Extreme muscle stiffness
- Diarrhoea, nausea, or vomiting
- Tremors or twitches in the eye or lower extremities
- Seizures
Serotonin syndrome treatment
Serotonin syndrome generally warrants an overnight hospital stay. Many patients receive oxygen, IV fluids, and other medications to regulate their blood pressure and heart rate, Dr. Samuel says. Going forward, patients are usually advised to stop or reduce the medication that caused the syndrome’s onset, Dr. Samuel says. Note: Do not stop taking medication without close medical supervision.
The upshot: Could you have low serotonin?
Serotonin’s many functions are just beginning to be understood. Mounting evidence indicates that the brain messenger plays a role in mood, appetite, weight, sleep patterns, sexual function, immune and GI function, cognitive function, and pain perception.It
’s important to consult with a qualified medical professional if you suspect your serotonin levels are less than optimal. The research community is still working to define “healthy” levels of serotonin, and currently there’s no easy way to measure a person’s specific serotonin function. While changes to diet and lifestyle may influence your serotonin levels, your mood, appetite, ability to manage weight, and sleep quality depend on many factors—not just your “chemical balance.”
This content is for informational purposes only and does not constitute medical advice, diagnosis or treatment. It should not be regarded as a substitute for guidance from your healthcare provider.