Is the idea that a nightcap helps you sleep just a fantasy? The scientific reasons why alcohol ruins sleep
A drink after work, right before bed.
"I can't sleep without it" or "I fall asleep right away when I drink"—there are probably many people who feel this way.
In reality, while alcohol may help you "fall asleep," it significantly ruins the "quality of your sleep".
Feeling sluggish the next morning or waking up suddenly in the middle of the night.
These might be side effects of your nightcap.
In this article, we will scientifically examine the relationship between alcohol and sleep.
Why does drinking alcohol make you sleepy?
First of all, it is true that alcohol makes you sleepy.
According to the Hoya Station Front Heart Clinic, alcohol binds to receptors in the brain called GABA receptors, which have the effect of suppressing nerve excitement.
GABA is a neurotransmitter that calms brain activity.
As alcohol enhances the function of GABA, it creates a sense of relaxation and drowsiness.
In other words, it is scientifically correct that "drinking makes you sleepy."
The problem lies beyond that.
The reason why you are sleeping but "not resting"
Even if you fall asleep after drinking, your body is not resting properly—the key to this lies in REM sleep.
REM sleep is a stage of deep sleep necessary for the brain to organize memories and stabilize emotions.
According to an explanation by the Sleep Primary Care Clinic, acetaldehyde, which is produced when alcohol is broken down in the body, is said to inhibit this REM sleep.
Furthermore, in the latter half of sleep, the blood alcohol concentration drops rapidly, causing a "rebound phenomenon" where the brain shifts toward an awakened state.
This is the cause of waking up suddenly in the middle of the night or early morning.
Summary of points: Differences in sleep with and without alcohol
Is "a little bit is fine" true?
You might think, "Then, isn't a small amount okay?"
However, the latest research has confirmed that even with a low dose (about 1 to 2 medium bottles of beer), the duration of REM sleep is statistically significantly shorter.
The "Guidelines for Alcohol Consumption with Consideration for Health" published by the Ministry of Health, Labour and Welfare in 2024 also explicitly states that drinking to resolve insomnia is a practice that should be avoided.
In addition, the same guidelines define the amount of alcohol consumption that increases the risk of lifestyle-related diseases as 40g or more of pure alcohol for men and 20g or more for women.
A guideline for 20g of pure alcohol is about one medium bottle of beer (500ml), one serving of sake, or two glasses of wine.
Reference amount for 20g of pure alcohol
A "replacement" habit to stop the nightcap
For those who have a habit of a nightcap, it is difficult to just be told to "stop."
What is important is to find "another habit" that allows you to relax instead of alcohol.
Ashita no Clinic points out that by continuing to have a nightcap, the brain develops a "tolerance" to alcohol, creating a risk of falling into a vicious cycle where you cannot sleep with the same amount and the quantity increases.
Actions you can try starting tomorrow:
Try replacing your nightcap with hot milk or caffeine-free herbal tea one hour before bed.
Warm drinks temporarily raise your core body temperature, and the subsequent drop in temperature promotes natural sleep onset.
Summary
While it is true that alcohol helps you fall asleep, it is only a "kindness at the entrance."
To protect the quality of your sleep, it is important to gradually incorporate relaxation methods other than a nightcap.
Try a warm cup of tea instead of a drink tonight.
That small choice might just change how you wake up tomorrow.
References
Ministry of Health, Labour and Welfare, "Guidelines for Health-Conscious Drinking" (Published 2024)
Hoya Station Front Kokoro Clinic, "Is alcohol related to GABA?"
Sleep Primary Care Clinic, "Alcohol and Sleep"
Ashita no Clinic, "What happens if you keep having a nightcap? Explaining the effects on sleep and the risk of dependency"
Banno Clinic, "On the relationship between sleep disorders and alcohol"
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