ABSTRACT
ABSTRACT Melatonin is a hormone secreted mainly by the pineal gland in the brain, and its secretion is controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus, the central biological clock responsible for circadian rhythms. Daily exposure to light resets the phase of the clock in the SCN. Tryptophan is the precursor of melatonin and its intake increases the availability of melatonin in the body. In this chapter, the sequence of the metabolism of tryptophan is described and the relation between tryptophan, melatonin, and human health is discussed. One study that investigated effects of tryptophan intake and light exposure on sleep and melatonin secretion is introduced and discussed with regard to the importance of daytime light exposure for melatonin secretion at night and the existence of a combined effect of light and tryptophan intake. The effects of the timing of pure tryptophan intake on mood, melatonin secretion, and sleep require further study.
