Alcohol and sleep

1

What does a drink do to your heart at night?

After drinking, the heart ran faster and recovered less in the first hours of sleep, even at about one drink.

A Finnish team asked a plain question: what does an evening drink do to a body that is asleep? They used heart monitors that log every single beat. 4,098 employees, average age 45, wore one through ordinary days and noted their drinks for each day.¹

The trick was the comparison. Each person had at least one day with alcohol and one without, so each was measured against his or her own dry nights. The team looked at the first 3 hours of sleep, where the authors say most deep sleep typically occurs.¹

After drinking, heart rate ran higher and heart rate variability, the small beat-to-beat shifts in timing, ran lower. The team read this as more work for the body's alert branch, less for its calming branch, and less recovery.¹

This study watched people live their lives. Drinks were self-reported, and a night with drinks may differ in other ways, such as a late evening.¹

2

Does the amount matter?

Yes. The more people drank, the bigger the change, and the smallest group already showed it.

The team sorted the people into three groups by their dose. The low group averaged about one drink, the moderate group about three and the high group about seven. A drink counted as 12 grams of alcohol.¹

Heart rate ran about 1 beat a minute faster after the low dose and nearly 9 faster after the high dose.¹

45 minless recovery in the first 3 hours of sleep, on average, for an 80 kg person after five drinks¹

The shape of the night changed too. Without alcohol, recovery built up as the hours went by. After high intake it did not. After low intake, the authors saw the readings move back toward normal by the third hour, judged by eye.¹

Drinks were reported once a day, with no times. The authors say the higher intakes may have been underestimated.¹

If your usual evening is a single drink, that is what the low group typically had. The change in that group was the smallest, but it was there.¹

3

Is that just real life being messy?

A lab trial with a no-alcohol night found the same direction in 26 adults.

A team at SRI International in California tested it with a no-alcohol night for comparison. It had 26 healthy adults, aged 30 to 60, sleep three nights in the lab. Before bed they got, in a balanced order, no alcohol, a low dose or a high dose.²

Low meant one standard drink for women and two for men. High meant three for women and four for men. Breath alcohol at bedtime reached about 0.05% after the high dose.²

Nights with alcohol looked like the Finnish ones. Heart rate rose, and the variability that comes from the calming nerve, the vagus, was suppressed. The changes were pronounced after the high dose. Their pattern across the night differed between men and women.²

One more result showed in women only, 11 of the 26. Their systolic blood pressure rose more in the morning hours after the high dose than after the low dose or placebo. That is a small group, so it is a lead, not a rule.²

If your evening is one drink, or two if you are a man, you are at the lab's low dose. The authors still reported marked effects at moderate doses.²

4

Does a drink help you fall asleep?

Only high doses made sleep start sooner. Even a low dose disturbed REM sleep in the pooled data.

A team in Australia pooled 27 studies of healthy adults who drank before sleep. They looked at how sleep itself changed, and how that depended on the dose.³

REM sleep, the stage with rapid eye movements, when most vivid dreams happen, started later and lasted less. Doses of 0.50 grams per kilogram or less, about two standard drinks, already disturbed it. More alcohol disturbed it more.³

Falling asleep sooner, and reaching deep sleep sooner, showed up only after a high dose: 0.85 grams per kilogram or more, about five standard drinks. The authors say a high dose likely makes the later REM disruption worse.³

For total sleep time, sleep efficiency and time awake in the night, the effect could not be pinned down.³

Falling asleep sooner is the part you can notice. The REM changes happen once you are already asleep.³

5

Does it hit everyone the same?

Mostly: in the Finnish data it held for both sexes and for active and inactive people, though heart rate rose more in younger ones.

The Finnish team checked who was affected. The drop in recovery looked similar in men and women, and in physically active and sedentary people. Regular exercise did not protect.¹

Younger people's heart rate changed more. At 0.75 grams per kilogram, heart rate rose 1.8 beats a minute more in a 30-year-old than in a 60-year-old. People whose heart rate in sleep is usually lower also lost more recovery.¹

Similar does not mean identical. The lab trial found different patterns in men and women, and both studies average over many people. Your own nights can differ.^1,2

Your watch shows your usual sleeping heart rate. If it is low, the Finnish data suggest a drink may cost you more recovery than it did for most.¹

6

What about snoring and breathing?

In pooled sleep-lab studies of 279 patients, alcohol went with more breathing pauses and lower oxygen at night.

A US team pooled 13 sleep-lab studies of 279 patients who snore or are prone to sleep apnea. Their breathing was recorded with and without alcohol.⁴

The apnea-hypopnea index, or AHI, counts breathing pauses and shallow breaths per hour of sleep. It rose by about 4 events an hour with alcohol, and the lowest oxygen reading was about 3 percentage points lower.⁴

These were people already prone to snoring or apnea. The review does not say the same size holds for everyone.⁴

If a partner says you snore more after a drink, this fits the pooled finding. The review used sleep labs, not watches.⁴

7

What does this mean for you?

The change grew with the amount, and the lowest Finnish group already showed it. The Finnish data had no drink times.

1. On your watch. On average, a night with drinks looked like a faster sleeping heart and lower variability in the first hours. One person's night can differ.¹
2. The dose. The group with about one drink still showed the change. The pooled data found REM disturbed at about two standard drinks or fewer.^1,3
3. The clock. The Finnish data had no times for the drinks, so it cannot say how early is early enough.¹
4. Snoring, or sleeping badly most nights? Ask your doctor. Alcohol went with worse breathing in people prone to snoring and apnea.⁴