Study details

For the study, researchers had 17 participants log their drink consumption and their quality and quantity of sleep for six weeks.

On average, the researchers found that caffeine reduced sleep quantity by 10.4 minutes per cup consumed the previous day, and those who drank alcohol the previous day predicted almost a 4% average decline in their sleep quality.

However, the researchers found that when participants drank both caffeine and alcohol, the negative impacts on sleep seemed to offset each other.

"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, lead researcher on the study and a fourth-year clinical psychology doctoral candidate at the University of Washington's 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," Song added. "And this was very intriguing to us."

Discussion

Historically, caffeine and alcohol both have been associated with negative impacts on sleep, but this study may be among the first to combine the real-world effects of both alcohol and caffeine on the quality and quantity of sleep.

"Independently, they disrupt sleep. So, it looks like that was what they found out as well is that independently they disrupted sleep," said Jill Waggoner, a family physician. "The caveat for this study was that they studied them together, which had never happened before."

While it appeared the negative sleep effects of alcohol and caffeine offset each other, the researchers said they believe this effect is only short-term.

"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," Song said.

He added that, despite the fact that participants were getting less sleep, they didn't notice a decrease in sleep quality.

"This concerns us and leads us to believe in the long run, it actually perpetuates this cycle of alcohol and caffeine use while the individuals are unaware of the negative effects on sleep," Song said.

Song added the study also found that participants turned to self-medication to offset the effects of alcohol or caffeine.

"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," he said. "And they will try to mitigate that with caffeine use in the daytime."

Ultimately, Song said the main takeaway of the study is that people can modify their alcohol and caffeine intake in order to improve their sleep, though the researchers stressed they aren't suggesting anyone drink an excessive amount of either and added that more research is needed to fully understand the effects of both. (Bourgeois, "Changing America," The Hill, 11/14; Walton, NewsNation, 11/10)

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