So, sleepy, why the warm milk?
Is it an old wives' tale?
Something we cling to as an educated man holds (perhaps in secrecy) his few superstitions, a tie to the past, an eccentricity, a psychological boost?
Warm milk is a traditional antidote to insomnia. Nannies and butlers and grandmothers and kindly innkeepers, all the caretakers of our cultural cast of characters, can be seen with the steaming mug in hand, backlit in a yellow lighted doorway. Perhaps the wind is howling outside. Perhaps the weather is devilish bad, and you'll catch a chill if not your death. Your nerves need soothing.
Milk of course has symbolic links to mothers and security, purity and luxury, but who can say if the sleep-searcher is working on a semiotic level?
Comfort.
The warmth of the beverage, perhaps helping to raise your body temperature slightly. The tactile sense of the mug between your hands, and perhaps steam, and above all the feel of warm creaminess on tongue and palette and throat. Perhaps it is augmented with nutmeg or whiskey1 or chocolate. A fire in the grate, or a handmade quilt, or a cat on your feet. This could be it.
Ritual.
Some tell of padding downstairs to heat the milk, the same pan, the same mug, the time alone, quiet, to calm and center oneself. While one is engaged in a ritual, one is in ritual time, outside of the banal. For some, that is enough to quiet the mind that races in the dark. A cup for me and two spoonsful for the cat. We drink together and look out the window at the rain. Rinse the mug, set it aside, walk up to the warm occupied bed. A meditation.
Nostalgia.
We learn old wives' tales from mothers, neh? And is it not known the powerful effect of the past on one's psyche? Perhaps it was drives in the car that put baby to sleep, or rubbing circles on her back, or a glass of warm milk and the presence of the beloved. What is to say that this will not work now? Herr Freud would like to hear your rejoinder.
Chemistry.
Milk contains tryptophan, which supposedly boosts serotonin levels in the brain. Some say there's not nearly enough tryptophan in a glass of milk to have that effect. Some suggest warm milk and a turkey sandwich to bolster the reaction2. Apparently, the chemistry of the proteins involved suggests that supplementing warm milk with carbohydrates (bread and honey, crackers and jam) will boost tryptophan (and serotonin) levels even more.
Another element in milk people suspect might be responsible for the nods are the casomorphins. Morphins. Opiates, albeit mild ones.
Nobody's got the solid answer to this one. For those suffering insomnia or just in need of soporific comfort, it can't hurt to try. For those in this situation who are also vegan or lactose intolerant, choose your reasoning from the first few categories and pick your milk substitute. We are as much mind as anything else. Many who report back on the efficacy of this treatment say that it works if they believe it will. Just as many other magics and medicines.
1 Whiskey, as well as other alcoholic beverages, are also traditional remedies for insomnia. Current wisdom holds, however, that as you get older you're more susceptible to rebound awakening: it'll put you to sleep, but it won't let you stay there. Alas!
2 Others warn against eating proteins just before bed, as they will supposedly make you more alert. So, so much for the gobbler.