Tryptophan

Tryptophan is one of the 20 standard amino acids used in human protein synthesis. It is an essential amino acid for humans, meaning it cannot be synthesized by the body and must be obtained from the diet. The biologically active form is L-tryptophan.

Chemically, tryptophan features an α-amino group, a carboxyl group, and a distinctive indole-containing side chain. It is classified as an essential aromatic amino acid.

Dietary sources include animal products such as meat, fish, eggs, and dairy, as well as plant foods like soy, legumes, nuts, seeds, and whole grains. Because it competes with other large neutral amino acids for transport across the blood–brain barrier, the amount and timing of protein and carbohydrate intake can influence its availability to the brain.

Biologically, tryptophan serves as a building block for body proteins and is a precursor to several important compounds. In the brain, it is converted to serotonin, a neurotransmitter involved in mood and sleep, and subsequently to melatonin, a hormone that helps regulate circadian rhythms. It is also metabolized via the kynurenine pathway, a route that leads to the production of nicotinamide adenine dinucleotide (NAD+) and other metabolites.

Safety and health: deficiency is uncommon in developed countries but can occur with malnutrition. In the late 1980s, contaminated tryptophan supplements were linked to serious disorders, resulting in regulatory action; improvements in manufacturing have reduced this risk. Supplements should be used with medical guidance, particularly when combined with other serotonergic medications.