You’ve probably heard about serotonin, the molecule known as the “happy hormone.” It’s widely thought to play a role in mood, sleep, learning, memory, digestion, and more—in fact, scientists think it has some impact on nearly every system in the body. So it’s no wonder that there’s an abundance of supplements on the market that claim to boost serotonin.
But despite its many assumed functions, serotonin’s role in the body isn’t well understood and its importance in things like mood is far from settled science. What exactly is serotonin—and will increasing it actually make you any healthier or happier?
What is serotonin and how is it made?Serotonin is a neurotransmitter, a chemical in the central nervous system that neurons use to communicate with each other. Outside the brain and spinal cord, it can act as a hormone, carrying messages between non-neuronal cells, says Jesse Bracamonte, a family medicine physician at the Mayo Clinic in Arizona. Studies suggest that “it can influence your mood, your learning ability, your libido, even wound healing,” says Bracamonte.
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Serotonin is mainly produced in the brain and the gut. In the brainstem, a cluster of neurons called the raphe nucleus take up the essential amino acid tryptophan, which is then converted into serotonin. Neurons in the raphe nucleus send tendril-like axons throughout the nervous system, says Bryan Roth, professor of pharmacology at the University of North Carolina School of Medicine.
While serotonin gets a lot of attention for its role in the brain, its role outside the brain might be just as significant. Only a small portion of the body’s serotonin is made in the brainstem while the majority—about 95 percent—is made by specialized cells that line the gut called enterochromaffin cells. Skin cells, lung cells, and cells involved in taste also produce small amounts of serotonin.
Even though only a small proportion of neurons in the body make serotonin, neurons throughout the brain have serotonin receptors, meaning they can likely recognize and respond to serotonin release.
“There are so many different types of receptors that are found in so many different types of neurons. This explains, to a great extent, the myriad effects of serotonin,” Roth says. For example, some serotonin receptors kickstart neuronal activity, while others quiet it.
What does serotonin have to do with mood? Researchers have long thought that serotonin has a role in regulating mood because drugs called selective serotonin reuptake inhibitors (SSRIs) are widely used for and effective at treating depression. These drugs prevent neurons from reabsorbing and breaking down serotonin, theoretically increasing the amount of it that is available in the brain.
But serotonin’s role in the brain is controversial. If you ask a serotonin researcher specifically how serotonin regulates any specific function—from mood to memory—the answer will likely be “I don’t know.”
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There’s evidence that neurons in brain areas involved in mood and cognition have serotonin receptors, and some studies show that serotonin influences learning. Roth argues that it’s likely involved in almost every neural circuit. Other scientists say that it’s more than likely that serotonin has some role in regulating mood.
However, Joanna Moncrieff, a professor of critical and social psychiatry at University College London, question’s serotonin’s role in mood and other cognitive functions. “We really don’t have good evidence that it has anything to do with depression. There is a bit of evidence that it might be involved in inhibiting sexual function, but that’s all,” she says.
So why would SSRIs work if serotonin doesn’t affect your mood? Roth explains that SSRIs only increase serotonin levels in the brain temporarily—and, ultimately, scientists don’t know how these drugs work, just that they do for some people, so more research needs to be done.
How does serotonin differ from dopamine? Serotonin is often compared to dopamine, another neurotransmitter that likely has many different roles in the body. But scientists are more confident about what dopamine does in the central nervous system.
Studies have shown that dopamine is involved in addiction and learning, and there’s strong evidence that it’s involved in brain circuits that predict how much of a reward you’ll receive. Dopamine is also thought to be involved in movement and goal-directed planning, but its role in these is less clear.
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What does serotonin do in the gut?Over the years, serotonin has also been shown to be involved in gut movement, secretion, and nutrient absorption. “Serotonin does a lot of things in the gut, but its primary function is to regulate gut contraction and motility,” says Damien Keating, deputy director of the Flinders Health and Medical Research Institute in Australia.
Studies suggest that serotonin is involved in metabolism, and mainly through controlling blood sugar and fat storage, says Keating. Studies have also linked serotonin to diseases of the gut, like IBS and long COVID.
So is it a good idea to take serotonin supplements? Despite how little we know about serotonin, many supplements claim to lift your mood by boosting your serotonin levels. Some of these supplements contain molecules 5-HT and tryptophan, two molecules that are converted to serotonin in the body. But there’s only limited evidence that they work, Bracamonte says.
Tryptophan, for one, is found in foods like many animal products, nuts, and legumes, and most people get plenty of it in their diets. Experts say that taking large amounts of it in pill form isn’t likely to do much to serotonin levels in the brain. Some studies have linked low tryptophan levels to worsening mood, but that’s only in people who already have depression—it didn’t do much to healthy people. On top of that, to get to the brain, tryptophan needs to cross the blood-brain barrier, and can only do this a little bit at a time, says Roth.
Worse, there are potential risks of taking these supplements. Serotonin is not absorbed well in the gut and might stick around, causing gut contractions that might make you feel nauseous or cause GI issues.
Another popular supplement is St. John’s wort, a medicinal plant that some scientists think might have a similar function to SSRIs and may be good for patients who can’t tolerate SSRIs. But there haven’t been enough high-quality studies to say for sure how well it works, Bracamonte says—cautioning that St. John’s wort also could have drug interactions so it’s best to talk to your doctor before using it.
There are also natural ways to trigger serotonin release, Bracamonte explains. Exercise, eating healthy, getting enough sunshine, and getting plenty of sleep. “Doing all of that helps mood and helps the body function better,” he says.
If you’re worried about your mood, ultimately Roth says that the best thing you can do is take the traditional route: “If you’re feeling depressed or anxious, talk to your family doctor,” he says.
Source : National Geographic