A current research printed in Sleep sheds mild on the connection between caffeine consumption and its influence on sleep. Researchers discovered that whereas a 100 mg dose of caffeine (roughly equal to 1 cup of espresso) might be consumed as much as 4 hours earlier than bedtime with out vital results on sleep, a 400 mg dose (corresponding to 4 cups of espresso) disrupts sleep when taken as much as 12 hours earlier than bedtime. Importantly, the findings reveal that folks typically wrestle to acknowledge the sleep disruptions attributable to caffeine, particularly when it’s consumed earlier within the day.
Caffeine is a extensively consumed stimulant used to boost alertness and counteract sleep deprivation. While prior analysis has highlighted caffeine’s basic influence on sleep, it lacked readability on how dosage and timing work together. The new research aimed to fill that hole by exploring how completely different doses of caffeine have an effect on sleep when consumed at numerous intervals earlier than bedtime.
With an estimated 40% of individuals worldwide struggling to get enough sleep and more and more counting on caffeine to handle fatigue, understanding the precise timing and amount that disrupts sleep is crucial.
“We have been on this matter as a result of there’s restricted proof to information clear suggestions on the dose and timing of caffeine consumption relative to sleep,” stated research creator Carissa Gardiner, a postdoctoral researcher on the SPRINT Research Centre on the Australian Catholic University. “With roughly 80% of the inhabitants consuming caffeine, it could contribute to the excessive charges of sleep insufficiency at the moment reported. Understanding how caffeine dose and timing of consumption have an effect on sleep can assist develop sensible tips to minimise the destructive influence on sleep.”
The researchers performed a placebo-controlled, double-blind, randomized research involving 23 wholesome male contributors aged 18–40 years. To take part, people needed to be reasonable caffeine customers (lower than 300 mg per day) with no medical situations or habits that may have an effect on sleep. Female contributors have been excluded to keep away from confounding results associated to hormonal cycles.
Each participant accomplished seven experimental situations over a 21-day interval. These situations included consuming both 100 mg or 400 mg of caffeine—or a placebo—at 12, 8, or 4 hours earlier than their typical bedtime. Participants adopted a constant sleep schedule, confirmed via wearable screens and sleep diaries. During the experiment, caffeine was administered in capsules, and saliva samples have been collected to confirm caffeine ranges within the physique. Sleep was assessed each objectively, utilizing a validated sleep-monitoring system, and subjectively, via participant-reported sleep high quality and period.
The findings highlighted a dose-dependent relationship, with increased doses inflicting extra pronounced disruptions to sleep. Specifically, a 100 mg dose had no measurable influence on both goal or subjective sleep outcomes, even when consumed as little as 4 hours earlier than bedtime. In distinction, a 400 mg dose precipitated disruptions to sleep even when consumed as much as 12 hours earlier than bedtime.
“Consuming 400 mg of caffeine inside 12 hours of bedtime can negatively influence sleep, with the consequences worsening the nearer caffeine is consumed to bedtime,” Gardiner instructed PsyPost.
When contributors consumed 400 mg of caffeine 12 hours earlier than bedtime, they skilled noticeable disruptions to their sleep structure, notably a discount in deep, restorative sleep (non-rapid eye motion stage 3). At this time level, whole sleep time was modestly diminished, and contributors skilled barely extra awakenings in the course of the evening.
These results turned extra pronounced when the caffeine was consumed eight hours earlier than bedtime. Sleep effectivity—calculated as the share of time spent asleep whereas in mattress—dropped by 7%, and contributors spent extra time awake after initially falling asleep. This timing additionally led to an elevated variety of nighttime awakenings and additional reductions within the period of deep sleep.
The most vital sleep disruptions occurred when contributors consumed 400 mg of caffeine 4 hours earlier than bedtime. Sleep onset latency—the time it takes to go to sleep—elevated by a median of 14 minutes, whole sleep time was diminished by roughly 50 minutes, and deep sleep period decreased considerably.
Sleep fragmentation additionally elevated, with extra frequent awakenings and the next proportion of lighter sleep levels. Subjective assessments aligned with these findings; contributors reported feeling much less rested and experiencing decrease sleep high quality once they consumed 400 mg of caffeine 4 hours earlier than going to mattress.
Interestingly, contributors had problem perceiving the complete extent of sleep disruptions attributable to caffeine, notably when it was consumed 8 or 12 hours earlier than bedtime. Although goal measures revealed vital will increase in nighttime awakenings and reductions in deep sleep, contributors’ subjective stories of sleep high quality and restfulness didn’t constantly replicate these disturbances. This mismatch between goal and perceived sleep high quality underscores the problem customers face in recognizing caffeine-induced sleep fragmentation, particularly when consumption happens earlier within the day.
“The mismatch between goal and subjective sleep was notably fascinating,” Gardiner stated. “Many folks imagine caffeine doesn’t have an effect on their sleep, however our findings counsel it could disrupt sleep even when people don’t understand it.”
The researchers additionally examined genetic variations associated to caffeine metabolism and sensitivity however was not giant sufficient to attract definitive conclusions. Larger research may higher discover how genetics mediate particular person responses to caffeine.
“My long-term aim is to proceed constructing the proof base to offer customers with clear, evidence-based steerage on how you can reduce caffeine’s influence on their sleep,” Gardiner stated.
The research, “Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial,” was authored by Carissa L Gardiner, Jonathon Weakley, Louise M. Burke, Francesca Fernandez, Rich D. Johnston, Josh Leota, Suzanna Russell, Gabriella Munteanu, Andrew Townshend, and Shona L. Halson.
