Mid-morning tryptophan depletion delays REM sleep onset in healthy subjects.

Because serotonin is involved in the diachronic regulation of sleep, we tested the effect of a midmorning rapid deficiency in the serotonin precursor tryptophan on the next night's sleep. After a 48-h low-protein diet, 17 healthy volunteers received either a tryptophan-free mixture of amino acids or a placebo at 10:30 A.M.