Serotonin is a neurotransmitter, or chemical passed between nerve cells, that's responsible for numerous functions in the body. Serotonin has been nicknamed the "feel-good" hormone in part because it seems to play a role in regulating mood, and specifically, in elevating mood. But this chemical messenger plays a role in everything from digestion, to sleep to bone health.
Theoretically, the concept of "boosting" serotonin might sound appealing, especially if it could help banish a low mood. But is it actually possible to boost serotonin, and what effect would this have on the body? Live Science spoke with experts to find out.
What is serotonin?
Serotonin is a neurotransmitter, a type of natural chemical released by the brain and the gut that enables communication between cells.
"Serotonin is synthesized using tryptophan, an amino acid that is not produced by the human body and needs to be supplied from the diet," said Dr. Teresa Poprawski, neuropsychiatrist and chief medical officer at Relief Mental Health, a clinic in Illinois. "Even though serotonin is often discussed in relation to the brain, nearly all serotonin can be found in the cells lining the gut and in the blood."
Only 1% to 2% of serotonin is found in the brain, although some sources state as much as 10%, Poprawski said.
Poprawski said that, in the brain and spinal cord, serotonin acts as a neurotransmitter, and in other tissues, it can act as a hormone.
"Serotonin produced in the brain acts as a neurotransmitter, but serotonin produced in the gut acts as a hormone," she told Live Science.
How does serotonin work?
The effects of serotonin in the body depend on whether it is acting as a neurotransmitter in the central nervous system (CNS) — which consists of the brain and spinal cord — or in other tissues as a hormone.
Poprawski said that in the CNS, serotonin is secreted into the synaptic cleft, the space between two nerve cells, or neurons. One neuron releases the serotonin and the other neuron receives it.
"The neuron that secretes serotonin also controls the amount of serotonin in the synaptic cleft by absorbing back the neurotransmitter, a process called reuptake," she said. "Certain drugs can slow down the rate of this reuptake, extending the effects of the serotonin on the receiving neuron." Selective serotonin reuptake inhibitors (SSRIs), for example, are a type of antidepressant used to prolong the effects of serotonin on the serotonin-responding neurons, she said.
As well as regulating mood, serotonin fine-tunes many functions of the CNS, including sleep, appetite, learning, memory and libido, said Poprawski.
Dr. Shaheen Lakhan, a neurologist based in Boston, Massachusetts, said that there has long been a belief that fluctuating levels of serotonin can directly affect our mood. However, neurotransmitters are more complicated than we previously thought, and there is a much more dynamic interplay between these brain chemicals and various functions of our brain, including mood and behavior, he said.
"Just as advances in smartphones are really driven by the interplay of hardware and software, neural circuits that connect at least two areas of the brain are responsible for complicated functions like mood, motivation, pleasure, cognition, memory and language," he said. "In other words, there is no one single part of the brain or single neurotransmitter that solely drives these functions. It is the hardware, software and energy axis that forms a brain circuit; and they aren't simply turned off or on, they are modulated."
Outside of the CNS, serotonin not only regulates intestinal functions, but also, when bound with platelets in the blood, regulates blood clotting and slows blood flow in the wound healing process, Poprawski said.
Serotonin is also synthesized into melatonin, both in the brain and the gut, she added. Melatonin is a hormone chiefly responsible for governing our circadian rhythm, which refers to the body's biological clock or natural sleep-wake cycle.
Do some people have more serotonin than others?
Like many neurotransmitters and hormones, some people produce more serotonin than others, because serotonin synthesis depends on multiple factors that vary between individuals, said Poprawski. "Aspects like [blood levels] of tryptophan and other large amino acids in relation to tryptophan will largely depend on individual dietary habits," she said.
Tryptophan hydroxylase is an enzyme that controls the rate of serotonin production. In turn, this enzyme's activity depends on gene expression, meaning which genes are switched "on" or "off," which is highly variable and influenced by genetics and environmental factors, Poprawski said.
Is it possible to "boost" serotonin production?
According to Poprawski, it is possible to increase serotonin production, but most people make adequate amounts of the chemical.
If levels are low enough to warrant medical intervention, doctors will need to determine why they fell in the first place..
Signs of low levels of serotonin can include anxiety, depression, lack of concentration, insomnia, overeating, and weight gain, among others.
Serotonin levels are usually low due to a deficiency in the precursor of serotonin, the amino acid known as tryptophan. Poprawski told Live Science that this can occur due to low levels of vitamin B6, folic acid or magnesium, a high-sugar diet, excess alcohol, and smoking.
"Production of serotonin in the brain can be increased, at least in theory, by dietary intake of tryptophan," she said. "This precursor to serotonin can enter the brain, but the carrier process also facilitates the entry of other, competing amino acids. In practice, the concentration of the tryptophan in the blood plasma will be directly affected by the concentration of competing amino acids." Even if tryptophan does get into the blood it has to compete with other amino acids to get absorbed into the brain where it can be used to produce serotonin.
So, theoretically, it is possible to "boost" serotonin production by consuming foods high in tryptophan, but it depends on other foods being consumed. Tryptophan is primarily found in protein-rich foods like poultry, lean pork, lean beef, salmon, soybeans, pumpkin seeds, squash seeds, tofu and eggs.
But Lakhan said that even though we may be able to boost serotonin production, this doesn't necessarily mean the body will be able to make use of the extra amount, particularly if we already have enough.
"You may see evidence of boosting serotonin through exercise, diet, nutraceuticals, and pharmaceuticals, but that only accounts for increasing your body's available battery, not the full function that it enables," he said. The brain is complex, and serotonin is not just involved in supporting mood. It also helps regulate attention, behavior and body temperature, as well as the production of melatonin, the sleep hormone.
In other words, there may be effective ways that we can increase serotonin production, and thus serotonin levels in the body, but this doesn't necessarily mean it will have any direct effect on your mood.
Ultimately, there is still more research that needs to be done in the area of neurotransmitter function and production. If you are concerned about low serotonin levels, speak with your doctor.
This article is for informational purposes only and is not meant to offer medical advice.
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Amber Sayer is a fitness, nutrition, and wellness writer and editor, and contributes to several fitness, health, and running websites and publications. She holds two masters degrees—one in exercise science and one in prosthetics and orthotics. As a certified personal trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, Amber likes running, cycling, cooking, spending time outside, and tackling any type of puzzle.