Many of us are aware that we get off to sleep quite easily when we drink large amounts of alcohol before bed, and its sedating effects sometimes mean that alcohol is used as a sleep aid in those that are having trouble sleeping. However, alcohol is very disruptive to sleep (some of us may have experienced this on nights where we’ve partied a little too hard).
Although the effects of alcohol on sleep have been studied for well over a hundred years, most of the research on specific aspects of sleep has been conducted since the 1930s. These early studies suggested that alcohol had a two pronged effect, with sleep structure and movement changing from the first to the second half of the night. These effects vary by the amount you drink.
The majority of laboratory studies investigating the effects on alcohol on sleep have given a single dose of alcohol shortly before bed, with the aim of peak blood alcohol concentrations at bedtime. If you go to bed with alcohol your system, you will likely take less time to get off to sleep, and you won’t wake as often during the first half of the night. You will, however, wake often during the second half of the night.
Your sleep structure will also change. The severity of these changes increases considerably with dose but overall, you will most likely have an increase in slow wave (deep) sleep in the first half of the night. However, this increase is at the expense of REM sleep. Your REM sleep, therefore, occurs much later in the night than usual, and the overall amount of REM sleep is decreased. The REM sleep that you do get is concentrated in the second half of the night. During REM sleep, our sympathetic nervous system activity is a lot more variable, and we have frequent changes in heart rate, breathing, and gut activity. We also don’t thermoregulate well. A nice combo which adds to that broken sleep.