You've probably heard of "Thanksgiving Day coma," a phenomenon whereby after eating a large turkey meal, you fall deeply asleep. Though it's not likely that tryptophan in the turkey is responsible for this effect -- there's simply not enough in the turkey meat -- there is truth to the assertion that tryptophan can make you sleepy.
Tryptophan
Tryptophan is an amino acid. Amino acids -- there are 20 common varieties -- are the building blocks of protein. They make up the proteins you eat, as well as the proteins in your body. You use amino acids, tryptophan included, to provide your cells with energy and allow them to make their own proteins. You can also use tryptophan to make serotonin, which is a neurotransmitter involved in feelings of relaxation.
Serotonin
Serotonin not only makes you feel relaxed, it can also make you feel sleepy, explains Dr. Neil Carlson in his book "Foundations of Physiological Psychology." Because your body makes serotonin from tryptophan, there's long been some suggestion that perhaps eating tryptophan-rich foods can have a serotonin-like effect on your body -- for instance, that you will feel sleepy after eating a tryptophan-rich meal.
Tryptophan and Sleep
There is some research that indicates tryptophan increases your feelings of reported tiredness, and can even impact how much sleep you get. A 1982 article published in the "Journal of Psychiatric Research" by Dr. E. Hartmann notes that this effect is measurable, though only in patients with mild insomnia. Normal individuals who don't have trouble falling asleep naturally don't appear to benefit from tryptophan, nor do they respond much to it at all.
Mechanism
While it's perfectly reasonable to hypothesize that the reason tryptophan makes you sleepy is that you make serotonin from it, there's actually evidence to the contrary. Some research published in a 1970 edition of the medical journal "The Lancet" suggests that the amount of REM sleep you get if you're given tryptophan isn't the same as the amount you'd get if you were given serotonin. This suggests that tryptophan affects sleep through some other mechanism than serotonin synthesis.
References
- "Foundations of Physiological Psychology"; Neil Carlson, Ph.D.; 2004
- "Journal of Psychiatric Research"; Effects of Image -tryptophan on sleepiness and on sleep; E. Hartmann; 1982
- "The Lancet"; Effects of L-Tryptophan On Human Sleep; R. Wyatt; 1970
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