Alcohol

What It Is

How much you drink, and how close to bed.

Why It Matters

Alcohol is widely used as a sleep aid, and the controlled evidence does not support it. In trials that gave healthy adults a measured dose, alcohol delayed and shortened REM sleep from roughly two standard drinks upward, while only a high dose, around five drinks, shortened the time taken to fall asleep, so the sedation people are chasing arrives at the dose that costs the most REM sleep. Those same trials could not settle what alcohol does to total sleep time, sleep efficiency, or time spent awake at night, which is the largest gap in this evidence. In prospective cohorts drinkers went on to report more sleep problems rather than fewer, though that signal came from moderate drinking and did not hold among the heaviest.

The clearest mechanism is breathing. Alcohol relaxes the muscles that hold the upper airway open, and in dosing trials it measurably worsened breathing during sleep and lowered overnight blood oxygen, with much larger effects in people who already snore or have sleep apnea. Those breathing events fragment sleep, which is what efficiency measures, though the only direct measurement of efficiency comes from a single small trial, where it fell at around five drinks. Genetic analyses point the same way for snoring, while finding no effect on how long you sleep, and habitual drinking raises the risk of being diagnosed with sleep apnea only slightly.

Keep the dose low, and put distance between your last drink and bed. In everyday tracking, sleep grows progressively shorter as the drinks go up, and drinking earlier eases the overnight strain on your heart without lengthening sleep. Do not treat a nightcap as a sleep aid, since it buys sedation at the cost of REM sleep. This is a modest lever rather than a fix: if you drink in the evening and sleep badly, moving your last drink earlier for a couple of weeks is a cheap way to find out what it is costing you.

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