Ask Dr. H: It's not tryptophan in milk that makes you feel sleepy

Question: For years, I've had a glass of warm milk to help me fall asleep. I think it works as well as a sleeping pill, but it's a lot safer and is natural - which I like. Is it the tryptophan in the milk that causes me to feel sleepy?

Answer: Warm milk at bedtime definitely can have a calming effect, but despite popular belief, it's probably not caused by the effect of the amino acid tryptophan on the brain. In order for tryptophan or any sleep-promoting drug to work, it must cross the "blood-brain barrier" and get from the bloodstream into the brain tissue. It turns out that all the other amino acids that collectively make up milk protein block the amino acid tryptophan from getting into the brain.

The "trick," researchers say, is to have a high-carbohydrate food just before drinking milk - like cookies or toast. Just remember to brush your teeth before going to bed! Carbs cause a spike in your insulin level, and that seems to make it somewhat easier for tryptophan to cross into the brain. Without that carb snack, the sedating effect of warm milk is probably due to the calming influence of a warm liquid and a belief in its results (i.e., a placebo effect).

A: Like a lot of new things, it was discovered by serendipity. In 1992, a doctor in a small Welsh town was conducting a research trial on a new drug to treat angina. While his findings were disappointing, he noticed that the experimental drug UK-92480 had the curious side effect of causing erections when tested on healthy male subjects. On March 23, 1998, after a number of years of further research, Pfizer received FDA approval for the use of Viagra to treat erectile dysfunction. Pop a pill one hour before sex - it became as simple as that.