The connection between tryptophan and serotonin is fairly straightforward. At a simplistic level, it could be thought of as a parent-child relationship, with tryptophan being the parent. The primary difference between tryptophan and serotonin is that tryptophan is an essential amino acid and a building block of plant and animal protein, and serotonin is a neurotransmitter. Tryptophan is a precursor of serotonin and must be available for its organic production; it is the only known supply source. In addition to directly influencing the levels of serotonin in the brain, tryptophan exerts a mild tranquilizing effect and helps to combat headaches, anxiety, depression and insomnia.
Unlike serotonin, tryptophan cannot be synthesized in the body and must be obtained through foods or nutritional supplements. Dietary sources of tryptophan and serotonin include protein-rich meat, cottage cheese, milk, brown rice, soy protein, tuna, shrimp and peanuts. After the digestive process has occurred, some tryptophan is bound up in proteins for storage, and the rest is absorbed into the bloodstream and transported to the brain, where one of two things will occur.
Most of the tryptophan that reaches the brain will enter the kynurenine pathway, with the end result being vitamin B3, also known as niacin. The remaining tryptophan will travel the other pathway and will be processed into 5-hydroxytryptophan (5-HTP). This is an intermediate stage along the serotonin-melatonin route.
The next conversion that takes place produces the chemical messenger known as serotonin. This neurotransmitter is responsible for transferring information from one cell to another during normal nerve and brain function. Serotonin is most concentrated in the gastrointestinal tract, platelets and the central nervous system’s hypothalamus, mid-brain and nerve endings.
Finally, serotonin must pass through an N-acetyl stage before being converted by the pineal gland into a neurohormone called melatonin. This hormone is a free-radical scavenger that plays an important role in healthy aging. It also helps set the body’s circadian rhythm by synchronizing the secretion of other hormones. Melatonin levels decline with age.
Dietary tryptophan supplements were recalled and later banned in certain areas of the world after some deaths and illnesses attributed to contaminants in the late 1980s. In some countries, supplemental tryptophan is available by prescription. In places where it’s banned as a single supplement, it can usually be found as a component in sleep-aid formulas. There are over-the-counter synthetic versions of 5-HTP based on extracts from the seeds of the Griffonia simplicifolia plant that can help increase levels of tryptophan and serotonin. Melatonin supplements are also available and are typically used as a sleep aid or to reduce jet lag.