Dose and timing effects of caffeine on subsequent sleep: a randomized 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, randomized crossover design, 23 males (25.3†±†5.0 years) with a moderate habitual caffeine intake (<300 mg∙day-1) completed seven conditions: placebo, and 100 and 400 mg of caffeine consumed 12, 8, and 4 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 100 mg dose of caffeine compared with the placebo (p†>†.05), but significant effects occurred with the 400 mg dose (p†<†.05). Significant delays in sleep initiation and alterations to sleep architecture were observed when 400 mg was consumed within 12 hours of bedtime (p†<†.05), and significantly greater sleep fragmentation occurred when 400 mg was consumed within 8 hours of bedtime (p†<†.05). Additionally, perceived sleep quality was significantly reduced when 400 mg was consumed 4 hours prior to bedtime (-34.02%, p†=†.006) but not at 8 or 12 hours. CONCLUSIONS: A 100 mg dose of caffeine can be consumed up to 4 hours prior to bedtime, but 400 mg 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 that individuals may have difficulty accurately perceiving the influence of caffeine on sleep quality. CLINICAL TRIAL REGISTRATION: Australian and New Zealand Clinical Trials Registry, registration number: ACTRN12621001625864, https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12621001625864.