When January rolls around, many people decide to give something up, whether it’s animal products or alcohol.
Alcohol actually shares qualities with what many people think of as its opposite - your morning cup of coffee. One key quality the two share is their tendency to harm the quality of your sleep, albeit in significantly different ways.
Interrupting sleep
You may think that alcohol makes sleep easier - and it often does make it easier to fall asleep - but this does not mean you won’t be tired the following day.
According to the sleep hygiene instructions designed by sleep psychologist Kevin Morgan, alcohol is quickly metabolised, leading to you waking up in the night multiple times from withdrawal. This withdrawal, the sleep hygiene instructions explain, is essentially the opposite of the drug, meaning that if alcohol makes one tired, then its withdrawal will make us restless.
A 2022 study explored this, finding that alcohol consumption - moderately and heavily - was a predictor of poor quality of sleep. Furthermore, the study suggested, it increased the risk of developing chronic sleep problems and therefore the risk to overall health.
Caffeine, on the other hand, is well-known for preventing one from sleeping. And it does. The sleep hygiene recommendations explain that the stimulating effects of caffeine can last between three and four hours after ingestion.
But it also affects the quality of sleep once you’ve actually fallen asleep, making it lighter.
A 2021 study exploring the affect of caffeine consumption on sleep quality found that caffeine could interrupt the quality of sleep if ingested one hour or less before bed. This affected both the ability to get to sleep, and the quality of the sleep itself. However, caffeine did not have a significant impact if consumed a longer time before this.
The main finding of the study was that consuming caffeine during the day, even in the afternoon, did not affect sleep quality, but consumption shortly before bed did. Indeed, more recent research has also shown the positives of coffee consumption in the morning.
“Poor quality sleep is characterised by tiredness (fatigue),” explains psychology professor Morgan.
“For most of us, such tiredness is short term, since it reverses following our next good sleep. However, if poor quality sleep is chronic (i.e. insomnia disorder), then fatigue is chronic as also are its [consequences] (impaired cognitive performance, reduced daytime efficiency, and mood dysregulation – tired people have less control over emotional reactivity).”
The impact of caffeine and alcohol on sleep, explains Morgan, will be greater on those who already have sleeping disorders.
To dream or not to dream
The two substances also can influence our dreams as well, and in a negative way.
“Caffeine increases the percentage of light (non-REM) sleep while alcohol actively reduces REM,” explains Morgan.
“Since we do most of our dreaming in REM sleep it follows that both of these substances reduce our opportunities to dream.”