When Maria Papova, the creator of Brain Pickings, was distilling the things she'd learned from doing seven years of blogging interestingness at a recent talk—like why you should cultivate the ability to change your mind, build pockets of stillness into your life, and appreciate how long it takes to do anything worthwhile— the cultural curator was tough on a gentle point: to "be as religious and disciplined about your sleep as you are about your work."
Why? Because every sleeping moment affects every waking moment: as we've covered before, sleep allows you to consolidate your memories (good for knowing things!), let your body relax (good for not feeling anxious all day!) and maybe even clean your brain (good for preventing dementia!).
Yet not all sleep is experienced equally: it's not just about the quantity of sleep you get, but the quality of the sleep. For instance, if you've had a hard workout during the daytime, you'll be more restful by the nighttime. But there's another factor that affects our sleep: what we put into our bodies. Namely, drinks.
We have a fun word for the practice of a late night beverage: a nightcap, which, WiseGeek tells us, comes from back in the 1700s when people would don a soft, silly hat to warm themselves and rest better. From our own firsthand research as undergraduates, we can say that an alcoholic nightcap is something analogous: alcohol sedates you and makes your blood vessels dilate, making you feel warmer.
There's even something slyly sophisticated and sexy about the pre-bed drink, summoning images of Jane Austen and Charles Dickens characters "retiring" to mahogony-lined libraries and sitting before fires
checking their iPhones discussing the last matters of the day. Even the New York Times is hip to this, saying that if you should nightcap, you should "stick with the classics: top-shelf whiskey, good brandy (usually Cognac), a burnished, potent, amber liqueur."
That warm coolness is cool if you want to employ an army of orphans or arrange games of whist, but not so much if you want to do your best work the next day. Because, as scientist Jordan Gaines Lewis says, a nightcap will disrupt your sleep—hampering the recuperation we spoke of above.
While alcohol has been shown to help you fall asleep faster, it makes you have lighter sleep in the second half of the night. You can thank that counterintuitive trend to the "rebound effect": as in your body adjusts to alcohol over the first half of your sleep, allowing you to sleep normally for the first part of the night—but then actually overcompensates in the second half, messing up your sleep.
Since we don't have a perfect picture of what happens during sleep, the reasons why, at a neuronal level, alcohol disturbs our sleep aren't quiet clear. If you feel like getting technical, head to Gaines's blog; for our purposes, we can borrow her insight that alcohol mimics one of our most important neurotransmitters—the chemicals that transmit signals from neurons to cells across synapses.
After an evening of drinking, the theory is that GABA dominates the first half of the night, allowing us to fall asleep (and deeply!). But once GABA is metabolized, much of it becomes the excitatory glutamate. And it's in glutamate-releasing brain regions like the reticular activating system (which partially modulates sleep/wake and arousal) where the midnight disruptions kick in.
In other words, your brain tries to make up for the weirdness that alcohol brings into your system—and that overcompensation prevents the full benefits of a full night's sleep. So avoid the nightcap, unless, as Gaines says, you make it an early evening one.