Re: How does the amino acid tryptophan aid in falling asleep?

I found the answer to your question contained on a web page published by 
Dr. Tim Gorski of Healthcare Reality Check.  Dr. Gorski is an Associate
Clinical Professor of Ob/Gyn at the Univiversity of North Texas Health 
Science Center.

Here's the link to the web page: http://www.hcrc.org/faqs/l-trypt.html

Dr. Gorski states,  "L-tryptophan is an essential amino acid and a 
metabolic precursor to serotonin. Serotonin acts as a chemical messenger, 
or neurotransmitter, in the central nervous system and appears to affect 
the sleep/wake state of arousal. Serotonin levels in the brain can be 
increased by the ingestion of L-tryptophan, and this has been shown to 
hasten the onset of sleep in humans."

It should be noted that he warns against ingestion of relatively large 
amounts of tryptophan supplemnts.  Dr. Gorski states, "What harm might 
there be in having chronically (or intermittently) increased levels of 
tryptophan in the blood? No one knows. But here, unlike the situation with 
respect to some other scientific propositions, the null hypothesis is that 
a substance is unsafe until it is proven safe. Otherwise, consumers become 
the guinea pigs of supplement promoters."

He states, "Just because a little is good doesn't mean that more is better. 
Therefore, before a drug or "supplement" is promoted as being safe and 
effective for a given purpose, there should be adequate evidence to support 
the claims made for it. And the burden of providing such evidence, of 
course, falls on those who make the claims."