Summary: A new study turned previous assumptions on their head, finding that alcohol and caffeine may offset each other’s negative effects on sleep when consumed together.
Over a six-week period, financial traders’ sleep logs revealed that the combined use of caffeine and alcohol didn’t exacerbate poor sleep as expected but showed a complex interplay that affected their sleep patterns.
While caffeine and alcohol individually decreased sleep quality and quantity, together they created a cycle of ‘self-medication’ with the alertness from caffeine masking alcohol’s impact on REM sleep, leading to a potentially harmful cycle of use.
Caffeine alone reduced sleep duration by 10 minutes per cup, while alcohol decreased perceived sleep quality by 4% per drink.
The study involved a group of financial traders, known for high-stress jobs and the regular use of caffeine and alcohol.
The combined effect of caffeine and alcohol on sleep was less detrimental than previously believed, revealing an unexpected interaction that could lead to a negative cycle of consumption.
Source: University of Washington
The first known study to look at the combined real-world effects of alcohol and caffeine on nightly sleep quality and quantity came up with an unexpected finding—at first.
Researchers at the University of Washington School of Medicine’s Center for the Study of Health and Risk Behaviors and the University of California, Berkeley’s Center for Human Sleep Science hypothesized that combined consumption of the two most popular psychoactive drugs in the world would degrade how well we sleep and for how long.
The assumption was based on decades of study of alcohol and caffeine independently. But a small cohort of financial traders who regularly consume alcohol and caffeine reported unexpected results.
“Compared to the nights when you might have one or the other, we thought we were going to see additional decline in subjective sleep quality or sleep duration,” said Frank Song, a researcher and fourth-year clinical psychology doctoral candidate in the UW Department of Psychiatry and Behavioral Sciences.
“But actually, that interaction effect was the opposite of what we expected and ended up having an effect of offsetting each other’s negative impact on quality or quantity. And this was very intriguing to us.”
Alcohol and caffeine’s interactive effects revealed themselves over the length of the six-week micro-longitudinal study. Song said some participants even showed signs of cyclical self-medicating with the effects of one drug being used to overcome the use of the other.
“It’s a very, very nice thought, I think, in many people’s minds that you could just use caffeine to wipe off the hangover,” Song said.
“But what we find is that while there may be greater alertness in the short term, it creates a sleep-state misperception contributing to continued use despite negative effects on sleep.”
The research appears in the journal PLOS ONE. Researchers found that 90% of adults have at least one caffeinated drink a week, while 74% of people 15 and over regularly have a drink containing alcohol.
“The global estimate is that for all persons aged 16 or older, the average alcohol consumption is 6.4 liters annually,” Song said.
Song, lead author on the study, chose to focus on financial traders because of the need for high attention and cognitive speed in their profession and known regularity of caffeine and alcohol use to mitigate the stress from work. Song himself was an investment analyst, working closely with financial traders, before turning to his doctoral studies in clinical psychology.
The group of 17 logged their daily drink consumption and sleep quality and quantity observations. The first two hypotheses they tested—how caffeine and alcohol worked independently—came back with unsurprising results.
Caffeine reduced sleep quantity by 10 minutes per cup consumed the previous day on average. Similarly, those who drank alcohol the day before reported a 4% decline in their subjective sleep quality per drink on average. Song considers both impacts significant.
The research group expected those negative impacts to continue when the two were combined in a pattern of daytime caffeine and nighttime alcohol use. They got the results they expected—eventually.
“Over time, it turns into a cycle of self-medication, as some may call it, in the real world where people will experience bad sleep as a result of alcohol-induced REM sleep suppression,” Song said.
“And they will try to mitigate that with caffeine use in the daytime. What we find is that despite caffeine leading to an objective reduction in sleep quantity, individuals did not perceive a reduction in sleep quality, suggesting a mismatch in perception that may contribute to continued alcohol and caffeine use despite negative effects on sleep.
“That can lead to a deleterious interaction and ultimately ends up being a negative cycle for their sleep.”
Alcohol and caffeine are two of the most commonly used substances for altering human consciousness. While their adverse effects on sleep have been separately examined in the laboratory and epidemiological levels, how they impact real-world night-to-night sleep, in isolation or together, remains unclear. This is especially true in occupations wherein the use of alcohol and caffeine is high (e.g., financial services sector).
Using a six-week micro-longitudinal study, here we examined the real-world impact of alcohol, caffeine, and their combined consumption in a cohort of financial traders.
We demonstrate that alcohol consumption significantly degrades the subjective quality of sleep (p < 0.001). Caffeine consumption led to a different phenotype of sleep impairment, resulting in a detrimental reduction in sleep quantity (p = 0.019), rather than a marked alteration in sleep quality.
Contrary to our hypothesis, when consumed in combination, evening alcohol consumption interacted with ongoing caffeine consumption such that alcohol partially mitigated the impairments in sleep quantity associated with caffeine (p = 0.032).
This finding suggests the sedating effects of alcohol and the psychoactive stimulant effects of caffeine obscure each other’s impact on sleep quantity and sleep quality, respectively–potentially explaining their interdependent use in this cohort (i.e., “self-medication” of evening sedation with alcohol to combat the prior daytime ingestion of caffeine and vice versa).
More generally, these results contribute to a unique understanding of the singular and combinatory impacts of two of the most commonly used substances for augmenting human consciousness under free-living, real-world conditions, the performance-impairing (and thus economic-cost) consequences of which may be important to the business sector and the society.