Dose and timing effects of caffeine on subsequent sleep: A randomised clinical crossover trial.

Study objectives: To investigate the effect of a typical dose of caffeine and a high dose of caffeine consumed in the morning, afternoon, and evening on subsequent sleep.

Methods: Using a placebo-controlled, double-blind, randomised crossover design, 23 males (25.3±5.0 years) with a moderate habitual caffeine intake (<300mg∙day-1) completed seven conditions: placebo, and 100 and 400mg of caffeine consumed 12, eight, and four hours prior to bedtime, with a 48-hour washout. In-home partial polysomnography and sleep diaries were used to assess sleep. Linear mixed models estimated the effect of each condition.

Results: No significant effect on objective or subjective sleep occurred with the 100mg dose of caffeine compared to the placebo (p>0.05) but significant effects occurred with the 400mg dose (p<0.05). Significant delays in sleep initiation and alterations to sleep architecture were observed when 400mg was consumed within 12 hours of bedtime (p<0.05), and significantly greater sleep fragmentation occurred when 400mg was consumed within eight hours of bedtime (p<0.05). Additionally, perceived sleep quality was significantly reduced when 400mg was consumed four hours prior to bedtime (-34.02%, p=.006) but not at eight or 12 hours.

Conclusions: A 100mg dose of caffeine can be consumed up to four hours prior to bedtime, but 400mg may negatively impact sleep when consumed as one dose within 12 hours of bedtime, with the adverse influence on sleep increasing the closer consumption occurs to bedtime. The discrepancy between objective and subjective sleep quality suggests individuals may have difficulty accurately perceiving the influence of caffeine on sleep quality.