There’s a good chance that what you think you know about the “happiness hormone” is incomplete.

Long associated with the brain and mood, more than 90 percent of serotonin is actually produced in your gut, where it plays a role in regular bowel movements and protection from disease. Like a single instrument in an orchestra, serotonin’s sound can be hard to isolate, but learning how it creates a symphony by interacting with numerous systems, other neurotransmitters, and the brain itself could improve your mental and physical health.

Serotonin is one of more than 100 neurotransmitters, or chemical messengers, in the human body. It helps regulate emotional stability, focus, sleep, sexual desire, and digestion. Scientists are only beginning to understand the various ways serotonin works throughout the body, but there are already evidence-based strategies that can help you maintain healthy levels naturally.

Serotonin has different roles depending on where it’s found and how it’s used.

What Serotonin Does in the Brain

A few hundred thousand serotonin-producing neurons concentrated in the brainstem send messages throughout the brain to influence emotions, mood, cognition, responses to stress, appetite, sleep, movement, and pain perception.

Although the gut’s serotonin can’t cross into the brain, your diet can still affect serotonin in the brain. That’s because the amino acid L-tryptophan—found in high-protein foods such as turkey, chicken, eggs, cheese, salmon, tofu, nuts, and seeds—does cross the blood-brain barrier, where the brain converts it into serotonin.

What Serotonin Does in the Gut

In the gut, where you find the majority of serotonin, it has a completely different job: regulating digestion.

Serotonin in the gut helps regulate appetite and gut motility—including speeding up digestion if your body needs to get rid of toxic or irritating foods.

“Our intestines have a rhythm, and when they are in rhythm, we feel well—our digestion is excellent,” Dr. Will Bulsiewicz, a gastroenterologist and author of “Plant Powered Plus,” told The Epoch Times. “And when our gut falls out of rhythm, you can feel unwell. You can have gut symptoms, abnormal bowel movements, constipation, or diarrhea.”

Here’s how it works: Specialized cells lining our digestive tracts sense food and then release serotonin, which binds to serotonin receptors on neurons in the gut that coordinate peristalsis, or the waves of muscular contractions that help propel food through the digestive tract. This explains why healthy serotonin levels contribute to regular bowel movements—and why digestive rhythm affects how you feel overall.

Other Roles of Serotonin

Serotonin in the brain is a precursor to melatonin—a hormone associated with the sleep cycle of the circadian rhythm. Serotonin in the gut is also a precursor to melatonin in the gut.

“A shocking discovery in researching my book was that we have 400 times more melatonin in our gut than we do in the [brain’s] pineal glands,” Bulsiewicz said. “What’s it doing there? Well, the answer is that melatonin is not just about sleep.”

In the gut, melatonin plays a role in regulating the immune system, he said. It has antioxidant properties that strengthen the gut barrier and protect gut microbes. Robust intestinal walls serve as a defense system against chronic inflammation and may help protect against neurological diseases such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis.

Serotonin also plays other roles. In skin cells, serotonin helps heal wounds by narrowing vessels and slowing blood flow so clots can form. Together with another neurotransmitter called dopamine, serotonin is also involved in sexual desire.

Supporting Healthy Serotonin Levels

You can influence your serotonin through simple lifestyle changes backed by research.

Get Morning Sunlight

Light exposure—especially in the morning—supports serotonin production and sets your circadian rhythm, the internal clock that coordinates everything from cortisol release to melatonin production.

“People in the winter tend to get the winter doldrums, and the treatment is light,” Bulsiewicz said. According to him, light plays a critical role in supporting serotonin production, allowing the body to function properly.

When light enters your eyes, it signals brain structures that trigger a healthy morning surge of cortisol (which energizes you) and sets up proper melatonin release 14 to 16 hours later (which helps you sleep). At night, melatonin activates immune system repair and restoration.

“In telling you that it’s time to go to bed, melatonin is orchestrating your nighttime circadian rhythm, which includes activation of the immune system in a good way because the immune system turns on at night to repair and restore your body,” Bulsiewicz said.

More morning light exposure was associated with lower depressive and stress symptoms, regardless of whether participants were taking anti-depressants called selective serotonin reuptake inhibitors, according to a study published in Biological Timing and Sleep. The authors noted that spending time outdoors could benefit not only patients taking medication, but also the general population.

Eat a High-Fiber Diet

In addition to foods that contain tryptophan, Bulsiewicz said, a high-fiber diet supports the production of short-chain fatty acids that help produce neurotransmitters.

The key, according to nutritional psychiatrist Dr. Drew Ramsey, is decreasing inflammation and increasing neurotransmitter production by avoiding ultra-processed food, he told The Epoch Times. The Mediterranean diet is a simple solution, he said, and was associated with 40 percent to 45 percent lower odds of moderate to severe depression in a study published in Nutrients.

“Every patient with depression and anxiety deserves a conversation about medications, psychotherapy, and fermented foods and plant consumption,” Ramsey said. “You can’t have good mental health without proper nutrition.”

Research has shown that probiotics, found in fermented foods such as yogurt, kimchi, and sauerkraut, increase serotonin levels in the gut. Other factors can also influence neurotransmitters, including smoking, diabetes, thyroid imbalances, and vascular health, he said.

Do Aerobic Exercise

Boosting your heart rate through exercise—no matter your age or how frequently you participate—has a positive effect on serotonin levels.

A randomized controlled trial gauging what intensity of exercise affects serotonin in a single exercise session found that high-intensity exercise—the kind that makes it hard to carry on a conversation—had significant effects on serotonin.

Another study of teen boys found that two hours of daily basketball training raised serotonin levels after eight weeks. A separate small study of sedentary women with the pain disorder fibromyalgia found that aerobic exercise—but not stretching—boosted serotonin and improved symptoms after 20 weeks.

The fibromyalgia study noted that low serotonin contributes to the disorder’s symptoms, including imbalanced hormones and neurotransmitters, nervous system dysfunctions, sleep disorders, and anxiety. Exercise, the authors said, is a low-cost, safe, and effective treatment for fibromyalgia, improving quality of life, mood, and psychological well-being.

Too Much of a Good Thing

Although supporting healthy serotonin is beneficial, too much can cause problems.

Excess serotonin in the gut may weaken bones, increasing the risk of fractures and osteoporosis. Too much serotonin can also cause nausea. Of note, nausea is also a common side effect of selective serotonin reuptake inhibitors and often warrants low initial dosing and close monitoring.

There’s also a serious but rare condition called serotonin syndrome, a reaction caused by medication interactions that can quickly raise serotonin levels in the body.

Lifestyle Predicts Serotonin

Bulsiewicz noted that much of what affects serotonin is hardwired into human biology—spending time outdoors, staying active during the day, and eating whole foods.

Leaning into these basic but sometimes overlooked needs, he said, is how we make ourselves healthy—and supporting sufficient levels of serotonin is part of that equation.

“I think it’s important to understand that the way we are designed and the way we evolved is very different from the way that we currently live,” he said.