Tryptophan is an essential amino acid, i.e. it is not produced endogenously and thus needs to be integrated in the diet; in addition, it represents on average only 1% of the amino acids taken, so its concentration in the blood can often be insufficient. L-Tryptophan is the sole precursor for the endogenous synthesis of serotonin, a chemical mediator that regulates mood, and of melatonin, the hormone produced by the pineal gland, whose action is essential during the various stages of sleep, especially during the REM stages.
