Consuming caffeine in the morning and early afternoon does not appear to harm one’s deep sleep at night, according to a new placebo-controlled study published in Scientific Reports. But the new research also suggests that the brain may enter a state of caffeine withdrawal during sleep at night if the stimulant has been repeatedly consumed during daytime.
“Daily caffeine intake during daytime is highly prevalent and the stimulant is well-known for its wake-promoting potential and its negative effects on deep sleep,” explained study author Carolin Reichert, a postdoctoral researcher at the University of Basel.
“The empirical evidence, however, supporting a sleep-disturbing effect of caffeine under conditions of daily intake during daytime is sparse. Specifically, it was unclear if sleep pressure (as measured by electro-encephalographic sleep-slow-wave activity) is dampened under these conditions. That was one of the main reasons to carry out this study.”
In the double-blind study, 20 male participants were assigned to a caffeine, a placebo, and a withdrawal condition. In the caffeine condition, they took a 150 mg caffeine pill once in the morning, once in the midday, and once in the afternoon for ten days, while in the placebo condition, the participants consumed an inert gelatin pill. In the withdrawal condition, they consumed 150 mg of caffeine three times a day but then abruptly switched to a placebo on the ninth day.
Reichert and her colleagues used a crossover design, meaning every participant completed all three conditions, but the order of the conditions was randomized for each person.
The participants, who had reported consuming about 300 to 600 mg of caffeine per day prior to the study, were also instructed to refrain from caffeinated beverages and food. The participants’ last dose of caffeine (or placebo) was consumed about 8 hours after waking up, leaving approximately 8 more hours until bedtime.
The researchers found no significant differences between the three conditions when it came to self-reported sleep quality. Similarly, an analysis of polysomnography data failed to turn up significant differences in total sleep time, sleep efficiency, sleep latencies, or the relative amount of sleep stages. In other words, caffeine consumption during the day did not appear to impact sleep structure or subjective sleep quality at night.
However, electroencephalogram data indicated that sigma brainwaves were reduced in both the caffeine and withdrawal conditions during non-rapid eye movement sleep, which “might point to early signs of caffeine withdrawal,” the researchers said.
“If we consume caffeine regularly during daytime, this might not necessarily dampen sleep pressure or the depth of sleep. The brain most likely tries to adapt to the daily presence of the stimulant,” Reichert told PsyPost.
“The other side of the coin is, however, that we might experience a kind of first withdrawal symptoms during sleep every night, when caffeine is at low levels and has been metabolized to a certain degree. The consequences of these nightly withdrawal symptoms are not yet known.”
As with any study, however, the new research includes some caveats.
“We investigated the effects of a specific dose of caffeine over 11 days in a specific sample of rather healthy adult young male caffeine consumers,” Reichert said. “Whether the effects can be similarly observed in other populations (e.g. other age, sex, or with specific medications or a specific genotype) remains to be determined. It is also unclear for how long the effect persists.”
The study, “The impact of daily caffeine intake on nighttime sleep in young adult men“, was authored by Janine Weibel, Yu-Shiuan Lin, Hans-Peter Landolt, Joshua Kistler, Sophia Rehm, Katharina M. Rentsch, Helen Slawik, Stefan Borgwardt, Christian Cajochen, and Carolin F. Reichert.