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Turkey is probably the most celebrated source of tryptophan, the amino acid thought to contribute to drowsiness after a big Thanksgiving meal. But it’s also found naturally in many other foods, including various meats, nuts and seeds, milk, and some fruits and vegetables.
In the body, tryptophan is converted into 5-HTP, which is then converted into serotonin. In other words, tryptophan and 5-HTP both act as precursors to the production of serotonin, an important hormone and neurotransmitter. Low levels of serotonin have been linked to depression, mood disorders, and insomnia. So getting a good dose of tryptophan from your diet or supplements can have positive effects on brain health. Here’s a look at the top four benefits of this important neurotransmitter:
1. Less Depression
Some of the human research has been done by testing the short-term effects of high- and low-tryptophan diets, which shows that consuming more dietary tryptophan resulted in less depressive symptoms and decreased anxiety. Women may be more susceptible than men to low tryptophan levels, and people with a history of depression are particularly sensitive. Studies have found that tryptophan supplements work as well as many antidepressant drugs. The beneficial effect of this amino acid on depression may be related to its ability to boost several neurotransmitters, including serotonin and dopamine (linked to pleasurable feelings).
Seasonal Affective Disorder (SAD) is thought to be a result of fewer hours of sunlight during the fall and winter. Studies have found that combining tryptophan supplements with a full-spectrum light box (mimicking morning exposure to sunlight) leads to improvements in people with SAD.
2. Deeper Sleep
Serotonin serves as a precursor to melatonin, a neurohormone that regulates the body’s sleep cycle. Tryptophan has been found to promote sleep, and it has the advantage of not causing morning grogginess. In one study, people who took an amino acid preparation containing 5-HTP took less time to fall asleep and saw improvements in sleep duration and sleep quality.
3. Quicker Thinking
Tryptophan may benefit cognition and mitigate aggressive behavior. A deficiency interferes with normal thinking processes, including learning, memory, recall, and mental flexibility. Conversely, maintaining an adequate intake (e.g., from turkey) may help preserve cognitive function. Both animal and human studies have found that serotonin inhibits aggressive behavior. In human research, tryptophan depletion increases aggressive behavior, especially in people who have a history of aggressiveness.
4. Better Gut & Microbiome Health
Our digestive systems are sometimes called the “second brain” because the digestive tract is the body’s only organ to house its own nervous system. Called the enteric nervous system, this neural network consists of 500 million neurons, five times the amount in the spinal column. So it’s maybe not surprising that tryptophan is a key nutrient in gut health, as well.
In a 2021 study published in the International Journal of Molecular Sciences, researchers from the Medical College of Georgia found that a diet lacking in tryptophan makes the gut microbiome less protective and increases inflammation. After just 8 weeks on a low-tryptophan diet, mice showed lower levels of Clostridium sp., bacteria that metabolize tryptophan and enable production of serotonin, in the gut. The low-tryptophan mice also saw a threefold increase in Acetatifactor, bacteria associated with intestinal inflammation. In fact, the low-tryptophan diet set the stage for inflammation body-wide, the researchers say, which in turn, affects the aging process.
“We think the microbiome plays an important role in the aging process and we think one of those players in aging is tryptophan, which produces metabolites that affect every organ function,” says Carlos M. Isales, MD, co-director of the Medical College of Georgia Center for Healthy Aging and a coauthor of the study.
Dosage Guidelines for Tryptophan
There are some considerations to keep in mind before you take either tryptophan or 5-HTP. First, effectiveness is influenced by other dietary proteins. Therefore, take supplements on an empty stomach at least 15 minutes before—or two hours after—eating.
Second, the recommended dosage for tryptophan is about 10 times higher than it is for 5-HTP. For sleep disorders, try 1 gram (1,000 mg) of tryptophan or 100 mg of 5-HTP before bed. For depression, try either 500 mg of tryptophan or 50 mg of 5-HTP three times daily, and take the last dose just before bed.