Why does warm milk make you sleepy but cold milk doesn’t?

A STAFF REPORT FROM THE STRAIGHT DOPE SCIENCE ADVISORY BOARD

Dear Straight Dope:

Why does warm milk help you sleep but cold milk doesn't?

Ken replies:

At least two things go into this:

1) Tryptophan: the same ingredient that makes everyone sleepy after Thanksgiving dinner is present in milk.

2) Warmth: the few degrees that this drink might raise your body temperature is often enough to trigger the slowdown response we have on warm days.

In addition there is anecdotal evidence that the warm milk reminds us of the time when we were infants, hence "sleep like a baby."

Most other beverages we enjoy warm tends to have caffeine, which inhibits sleep (coffee, hot chocolate/cocoa, leaf tea), but many herbal teas are as good as warm milk and in fact are recommended for the lactose-intolerant.

Send questions to Cecil via cecil@straightdope.com.

STAFF REPORTS ARE WRITTEN BY THE STRAIGHT DOPE SCIENCE ADVISORY BOARD, CECIL'S ONLINE AUXILIARY. THOUGH THE SDSAB DOES ITS BEST, THESE COLUMNS ARE EDITED BY ED ZOTTI, NOT CECIL, SO ACCURACYWISE YOU'D BETTER KEEP YOUR FINGERS CROSSED.

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