L-tryptophan: effects on daytime sleep latency and the waking EEG.

The effects of L-tryptophan (4 g) on the waking EEG and daytime sleep were studied in a group of 20 normal adults. Subjects were assigned to a morning or afternoon group, and data were collected on two occasions, after L-tryptophan and after placebo, assigned in a counterbalanced order. L-Tryptophan significantly reduced sleep latency without altering nap sleep stages and elevated plasma total and free tryptophan levels. EEGs were digitized on-line and later analyzed for changes in 5 frequency bands: 16-40 c/sec (beta), 13.0-15.5 c/sec (sigma), 8.0-12.5 c/sec (alpha), 4.0-7.5 c/sec (theta) and 0.5-3.5 c/sec (delta). During waking EEGs, L-tryptophan significantly increased alpha time, theta time, and theta intensity and significantly decreased alpha frequency. No wave bands were altered during sleep. L-Tryptophan is an effective daytime hypnotic which can facilitate sleep onset at clock times which do not coincide with biological sleep times. The hypnotic effects may be mediated by lowering arousal level during the awake state, thus setting the stage for more rapid sleep onset.