There are many things in modern society that can contribute to a restless night, from blue-light screens to the evening ruminations of a restless mind. Resting only gets more complicated when you add the substance-specific buzz of alcohol, nicotine, or caffeine, though research published Tuesday in Sleep reveals one of those three isn’t as bad for sleep as we once thought.
Relative to nicotine and alcohol, caffeine has enjoyed a reputation as a productivity tonic that’s fine — if not necessary — for work. There are costs to overdoing it on caffeine, but interrupted sleep, surprisingly, does not seem to be one of them.
Using data on the evening rituals of 785 African-Americans enrolled in the Jackson Heart Study, the researchers, led by Christine Spadola, Ph.D., an expert in social welfare at Florida Atlantic University, found that people who drank caffeine within four hours of bedtime experienced no significant impacts on sleep. Nicotine and alcohol, on the other hand, were a very different story.
Caffeine’s Effect on Sleep
Spadola says she was surprised by how many people were ready to gamble with their sleep quality for a hit of caffeine. She studied participants’ sleep quality by comparing their self-reported caffeine, nicotine, and alcohol habits with the readings from the wearable sensor each person wore to track sleep quality over an average of 6.7 nights each (a total of 5,614 nights).
Forty-five percent of the participants reported at least one evening of caffeine intake. By comparison, 19.6 percent reported drinking alcohol during the evening at least once, and 9.2 percent used nicotine.
“We were surprised at the number of people who reported consuming at least one caffeinated beverage within four hours of bedtime,” says Spadola.
Unlike nicotine, caffeine had no effects on a variety of sleep parameters, which include sleep efficiency — the percentage of time in bed actually spent sleeping — and “wake after sleep onset”, the amount of time spent trying to fall back asleep after waking up during the night.
That aside, Spadola cautions that it’s still too early to start chugging mid-afternoon espressos with abandon. This study didn’t investigate individual caffeine sensitivity (and this can be highly individualized), so these results may differ depending on the person.
“Because of this, we still recommend following general guidelines and limiting caffeine consumption after 12 noon for optimal sleep,” she says.
The Effects of Alcohol and Nicotine on Sleep
This study’s results are a good excuse to try an afternoon cup of coffee without fear of repercussions. But for anyone who still uses the phrase “nightcap” or finds solace in a late-night JUUL pod, the results are more sobering.
"We still recommend following general guidelines and limiting caffeine consumption after 12 noon.”
Unlike caffeine, nicotine and alcohol both had negative impacts on sleep, but they manifested in different ways.
Alcohol reduced sleep efficiency by about one percent, on average, though it had no effects on sleep duration. These findings, explains Spadola, are inconsistent with the idea that alcohol is actually an “common over-the-counter sleep aid.” While a nightcap may help people fall asleep faster, that sleep comes at a cost later on.
“The overarching research supports that while [alcohol] can help you fall asleep, it leads to more fragmented sleep in the second part of the night,” Spadola says.
Nicotine also affected sleep efficiency, reducing it by 1.74 percent over the course of the evening. Unlike alcohol, however, it also increased the number of restless minutes spent lying there, trying desperately to sleep after a random awakening. An evening of nicotine use was associated with an average of six more minutes of that feeling compared to an evening without it.
Taken together, the team’s results are evidence that none of these common substances are great before bedtime, though they point out that the major drawback to their study is that it doesn’t involve any data on the dosage of alcohol, nicotine, or caffeine that any person consumed before bed. But it gives a broad glimpse of the effects of the three as well as a suggestion about which of them comes with more specifically sleep-taxing side effects.
Methods: Participants in the Jackson Heart Sleep Study underwent wrist actigraphy for an average of 6.7 nights, and completed concurrent daily sleep diary assessments to record any consumption of alcohol, caffeine, and nicotine within 4 hours of bedtime. Linear mixed-effect models were fit and adjusted for age, sex, educational attainment, body mass index, depression, anxiety, stress, and having work/school the next day. Results: Eligible participants (n=785) were an average of 63.7 years (SD: 10.6), and were predominantly female (67.9%). There were 5,164 days of concurrent actigraphy and sleep diary data. Evening alcohol use was associated with that night’s lower sleep efficiency [-0.98% (95% CI: -1.67% to -0.29%), p=0.005], but not with WASO or sleep duration. Evening nicotine use was associated with that night’s lower sleep efficiency [1.74% (95% CI: -2.79 to -0.68), p=0.001] and 6.09 minutes higher WASO [(95% CI: 0.82 to 11.35), p=0.02], but was not associated with sleep duration. Evening caffeine use was not associated with any of the sleep parameters.
Conclusions: Nicotine and alcohol use within four hours of bedtime were associated with increased sleep fragmentation in the associated night, even after controlling for multiple potential confounders. These findings support the importance of sleep health recommendations that promote the restriction of evening alcohol and nicotine use to improve sleep continuity.