(Trp, L-tryptophan)

A dietary essential amino acid and a building block of proteins. Tryptophan must be consumed daily because the body cannot synthesize it. In addition to serving as a raw material for proteins, tryptophan is required for the synthesis of serotonin, a neurotransmitter that helps conduct nerve impulses between cells. Serotonin is also released by mast cells, defensive cells embedded in tissues, and by blood platelets. Serotonin causes smooth muscle to contract; it functions as a vasoconstrictor to constrict blood vessels. Dietary sources of tryptophan include pineapple, turkey, chicken, yogurt, unripened cheese, and bananas. The usual diet provides 1 to 2 g daily spread out over time, rather than as a single dose.

Tryptophan supplementation has been used with the following conditions:

Depression Depression is a facet of many diseases and tryptophan, together with painkillers, may help unresponsive depression in some cases. Tryptophan supplements in combination with vitamin B₆ have been tested as antidepressants. The effects of tryptophan on mania and aggressive behavior have also been examined clinically. Its use has been criticized as being less effective than standard drugs.

Food Cravings Administering a combination of tryptophan and tyrosine has been used to help with depression and craving during withdrawal from addictive substances.

Difficulty in Sleeping The effectiveness of tryptophan for inducing sleep is well established. Tryptophan has been used for many years in Great Britain to treat insomnia. For certain people, it enhances relaxation and sleepiness. Tryptophan seems more effective when taken before bedtime with a carbohydrate-rich food.

Side Effects from Oral Contraceptives Women taking oral contraceptives may metabolize tryptophan abnormally, which may be helped by taking vitamin B₆.

Chronic Pain Research suggests that tryptophan partially reduces sensitivity to pain. Administration of small doses of tryptophan throughout the day with a high carbohydrate, low-fat, low-protein diet and appropriate medication can decrease symptoms in some people. More research in this area is needed.

Toxicity and Side Effects

Amino acids are powerful agents in the body. Amino acid research in humans is still considered preliminary, and the long-term effects and safe dosages are not known for many situations. The Centers for Disease Control linked large doses of tryptophan supplements to a rare, painful blood disorder called eosinophilia-myalgia syndrome (EMS) that became an epidemic in 1989. Subsequently, the U.S. FDA issued a nationwide recall of all tryptophan products in which this amino acid is the sole or the major constituent. The only products containing tryptophan not recalled include certain protein supplements, infant formula, and special dietary foods that contain small amounts of tryptophan for nutrient fortification. No cases of EMS have been reported from this use. EMS is marked by severe muscle pain, joint pain, difficulty in breathing, swollen limbs, and fever. In severe cases there are signs of congestive heart failure and paralysis. Most cases were associated with a tryptophan from a single manufacturer; it was contaminated with a related product. Moderate doses of tryptophan (as low as 1 g/day in certain individuals) may cause liver abnormalities. When used with antidepressants, side effects may worsen.

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