Tryptophan

About Tryptophan

L tryptophan is an essential amino acid with an indole side chain, first isolated from casein in 1901 by Frederick Gowland Hopkins and Sydney Cole. It is the precursor of serotonin, via 5 hydroxytryptophan, and of melatonin, and it can be converted into niacin. Only a small share is used for serotonin, and most is broken down through the kynurenine pathway, whose products such as kynurenic acid and quinolinic acid are studied in neuroinflammation. Its entry into the brain depends on competition with other large neutral amino acids, so carbohydrate rich meals can increase brain uptake, and the idea that turkey causes drowsiness is not supported. In 1989 an outbreak of eosinophilia myalgia syndrome was linked to tryptophan supplements made by the Japanese company Showa Denko, most likely due to manufacturing contaminants. The FDA recalled the products and restricted imports, restrictions that were eased in the early 2000s. Experimental tryptophan depletion can lower mood in some people with past depression, supporting a role for serotonin.