University of Washington researchers discovered an "unexpected finding" while studying the effects of alcohol and caffeine on sleep.
In the first known study analyzing the effects of "the two most popular psychoactive drugs in the world," researchers from UW and University of California, Berkeley, hypothesized that combining caffeine and alcohol would decrease sleep quantity and quality.
For six weeks, 17 study participants — who worked in financial trading, an occupation where the use of alcohol and caffeine is high, according to the researchers — logged their drink consumption and their quantity and quality of sleep.
At first, the study, published in the journal PLOS ONE, yielded unsurprising results: Alcohol and caffeine measurably affect snoozing.
On average, caffeine reduced sleep quantity by 10 minutes per cup consumed the previous day. Those who drank alcohol the day before reported a 4% decline in their sleep quality on average, according to the study.
But when consumed together, researchers found the negative impacts of caffeine and alcohol on sleep were offset.
"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," lead researcher Frank Song said in a statement. "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."
Researchers believe the offsetting effect lasts only for a short time, though.
In the long run, they believe combining alcohol and caffeine ultimately perpetuates a self-medication cycle of use.
"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."
Even though study participants were getting less sleep, they were not able to perceive a decrease in sleep quality, which suggests a mismatch in perception that may contribute to continued use of alcohol and caffeine despite negative effects on sleep, the researchers found.
This "ultimately ends up being a negative cycle for their sleep," the study said.
