Does alcohol wreck your sleep?

What does alcohol do to sleep?

It splits the night in two. Taken 30 to 60 minutes before bed, alcohol shortens the time to fall asleep, and some studies find increased slow wave sleep in the first half, particularly in people who had little of it to begin with. The second half is where the cost arrives.

Roehrs and Roth set this out in Alcohol Research and Health. As the alcohol is metabolised and clears, higher doses produce more waking and more light stage one sleep in the second half of the night, which researchers read as the body compensating for what happened earlier.

This is why alcohol feels like it helps. The part you are conscious of, falling asleep, genuinely improves. The part you are not conscious of gets worse.

What happens to REM sleep?

It is suppressed, and the effect scales with dose. Studies consistently find dose-dependent REM suppression during at least the first half of the night, with alcohol acting as a potent REM inhibitor.

The dose pattern is specific. Lower doses, around 0.5 to 0.64 grams per kilogram, produced a small median increase in REM as a share of sleep. At 0.75 to 0.8 the median was a 6.7 per cent decrease, and higher doses again showed suppression.

What follows is a rebound. REM tends to increase in the second half of the night as the suppression lifts, which is one plausible account of the vivid or unsettling dreams people report in the early hours after drinking.

Does your body get used to it?

To the helpful part, quickly. Tolerance to alcohol's sedative and sleep-stage effects develops within about three nights, after which the proportions of slow wave and REM sleep return toward baseline.

That is the trap in using a drink to sleep. Within a few nights it stops helping you fall asleep while continuing to fragment the night, and the obvious response is to drink more.

How much does this apply to you?

Somewhat less than the raw numbers suggest, and the authors say so. Studies administered larger doses than people typically pour for themselves, which may overstate the effect in ordinary life.

That cuts both ways. It means a single glass with dinner is unlikely to do what a laboratory dose does, and it means the direction of the effect is not in question, only its size at everyday doses.

The practical reading: the closer to bed and the larger the amount, the more of the night you lose.

What is worth doing?

Move it earlier rather than removing it. Finishing three or four hours before bed lets most of it clear before the second half of the night, which is the part that suffers.

Stop using it as a sleep aid specifically. It works for about three nights and then only the disruption is left, which is the worst possible trade.

If you track your sleep, alcohol is the single input most likely to explain a bad night, and it is usually more informative than any supplement you were considering.