“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.