Tryptophan is an essential amino acid that cannot be produced by the human body and must be obtained through your diet, primarily from animal or plant based protein sources. Tryptophan was discovered in the early 1900s after it was isolated from casein, a protein found in milk. Its molecular structure was determined a few years later.

Tryptophan plays a role in the production of serotonin, a mood stabilizer, melatonin, which helps regulate sleep patterns, niacin or vitamin B-3, and nicotinamide also known as vitamin B-6.

Over-the-counter use of synthetic tryptophan supplements were banned in the United States starting in 1989. However, tryptophan supplements were re-introduced in 2001 and are now available.

Why You Need Tryptophan
Tryptophan has the lowest concentration in the body of any amino acid, yet, it is vital for a wide variety of metabolic functions that affect your mood, cognition, and behavior.

Tryptophan elimination experiments have shown that tryptophan has a beneficial impact on:

Mood
depression
Learning
memory skills
visual cognition
Aggression control.
Research trials have shown it to have possible benefits when treating sleep disorders, seasonal affective disorder, premenstrual discomfort, and for reducing anxiety when quitting smoking. However, there is some disagreement on these results, indicating that more research is needed.

There is a common belief that tryptophan causes drowsiness. This has been associated with the U.S. holiday, Thanksgiving, where people who celebrate it report feeling tired after eating. Studies suggest that there may be some connection. Consuming large meals stimulates the production of insulin, and insulin clears the bloodstream of all amino acids except for tryptophan. In effect, insulin clears a path that can flood the brain with tryptophan.

However, there is uncertainty as to whether tryptophan causes this drowsiness. Insulin and large amounts of carbohydrates can also cause it. Additionally, there are other foods that contain more tryptophan than turkey, however, they aren't associated with drowsiness.

L-Tryptophan is an essential amino acid that cannot be synthesized by humans. It is typically found in both plant and animal based proteins. Most people consume more than double the amount that is actually needed, typically getting 900-1000 milligrams per day, while the US Recommended Daily Allowance (RDA) is 250-425 milligrams per day.

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