L-tryptophan is an an essential amino acid required for the production of serotonin in the neurones of the brain. In this role, tryptophan crosses the blood brain barrier and is converted to 5-hydroxytryptophan by the enzyme tryptophan hydroxylase, also the rate limiting conversion step, and then to serotonin via the enzyme amino acid decarboxylase. Low levels of serotonin are thought to increase the risk of depressive symptoms, and for this reason supplementation with tryptophan has been suggested as a possible treatment for certain types of mild depression. In this regard tryptophan appears to be effective in some people. Serotonin can in turn be converted to melatonin, a hormone that plays an important role at inducing sleep. Light inhibits the production of melatonin in the brain, but as light levels drop, melatonin synthesis increases and this may be the trigger for sleep. Low levels of tryptophan in the diet may therefore decrease melatonin production and may be a reason for disrupted sleep patterns or insomnia.
The effects of tryptophan on disrupted sleep has been investigated by researchers. In one study1, researchers investigated the effects of tryptophan depletion on sleep patterns in a group of subjects who had experienced insomnia previously but who were not taking medicine. The researchers administered an amino acid mixture that was absent of tryptophan, and this was designed to lower plasma levels of tryptophan by 70-90 %. As lower plasma levels of tryptophan lower brain levels of serotonin, this was an effective way to study the effects of serotonin depletion. Patients with insomnia experienced a drop in plasma tryptophan levels following consumption of the amino acid mixture compared to their baseline readings. In addition, following their amino acid drink, stage 1 sleep duration increased, but stage 2 sleep duration decreased and rapid eye movement sleep took on a more phasic characteristic. Tryptophan depletion there changes the sleep patterns of insomniacs and may affect the quality of sleep.
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