If you rely on a late-afternoon caffeine boost to get you through the rest of the day, your sleep could be taking a hit, according to a small new study.
The new research suggests caffeine can take a toll on sleep even when it's consumed six hours before bedtime.
"Drinking a big cup of coffee on the way home from work can lead to negative effects on sleep just as if someone were to consume caffeine closer to bedtime," study researcher Christopher Drake, Ph.D., an investigator at the Henry Ford Sleep Disorders and Research Center and associate professor of psychiatry and behavioral neurosciences at Wayne State University, said in a statement. "People tend to be less likely to detect the disruptive effects of caffeine on sleep when taken in the afternoon."
The study, published in the Journal of Clinical Sleep Medicine, included 12 healthy people with normal sleep patterns. For the four-day study, participants were instructed to maintain normal sleep schedules while taking three pills: one at six hours before bedtime, one at three hours before bedtime, and one right before bedtime. However, for three of the days, two of the pills were placebo pills and only one actually contained caffeine (400 milligrams' worth, the equivalent of two to three cups of coffee). That way, researchers could see the effect taking the caffeine pill would have on sleep when taken six hours before bed, three hours before bed, and right before bed. On the fourth day, all three pills were placebo pills with no caffeine.
The participants' sleep was measured both objectively and subjectively, with an in-home sleep monitor and recording entries in a sleep diary.
The researchers found that when the caffeine pills were taken at all three intervals of time, sleep was impaired. For instance, even taking the caffeine pill six hours before sleep resulted in less sleep -- by more than an hour -- that night.
"This degree of sleep loss, if experienced over multiple nights, may have detrimental effects on daytime function," the researchers wrote in the study. "Thus, the present results suggest the common practice of afternoon consumption of caffeine should at a minimum be restricted to before 5 PM, particularly with regard to the moderate-large doses of caffeine commonly found in increasingly popular premium coffees and energy drinks."
Recently, a study in the journal Sleep Medicine also showed that caffeine could take a toll on sleep -- but that this effect seemed to only apply to those who are considered "morning people." Specifically, the researchers found that "morning people" are more likely to wake up in the middle of the night than "night owls" if they consumed caffeine during the day, LiveScience reported.
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