Caffeine in doses ranging from 200-400 mg have been shown to be effective and are often utilized to sustain performance in the context of sleep deprivation, sedation, and sleep restriction.1–7 Up to 500 mg of caffeine can be found in commercially available 16-oz servings of brewed coffee.8 The use of similarly high doses of caffeine-containing beverages, including energy drinks has led to a doubling of caffeine-related emergency department visits from 2007-2011.9 The increase in ED visits in association with cardiovascular and other adverse events has been labeled a “rising public health problem in the US” and has led the Food and Drug Administration to investigate the cardiovascular safety of high caffeine content beverages.10 Importantly, the adverse effects of caffeine intake are not limited to the cardiovascular system but also produce significant sleep disruptive effects, particularly when taken later in the day or when multiple doses are utilized.11 One recent population-based study of 18- to 58-year-olds (mean age = 28.5 years of age) estimated that 90% of individuals consume caffeine in the afternoon (12:00-18:00) and 68.5% of people consume caffeine in the evening (18:00-00:00).12
Caffeine content in beverages and foods is increasing in terms of dose and availability, with recent estimates of total daily caffeine consumption suggesting that the average person consumes 319.32 ± 180.94 mg of caffeine per day.12 Information on the sleep-disrupting effects of high doses of caffeine taken in the afternoon and early evening is important, given the increasingly popular use of caffeinated energy drinks and the high caffeine content of premium coffee.13 Such investigations are also critical due to increased caffeine use in younger age groups, where chronic sleep restriction is also increasingly common.8,14,15 Indeed, recent data show that in younger samples, 37% report first use of caffeine during the day at 17:00 or later.16
Current Knowledge/Study Rationale: Despite widespread but often disparate recommendations to refrain from caffeine intake close to bedtime, no studies have investigated the effects of a given dose of caffeine taken at different times before sleep. Understanding the temporal effects of caffeine on sleep are important given the increased utilization of caffeine, and need for empirical data to support specific sleep hygiene recommendations regarding caffeine.
Study Impact: This study demonstrates caffeine consumption even 6 hours before bedtime can have important disruptive effects on both objective and subjective measure of sleep. These findings provide empirical support for sleep hygiene recommendations to refrain from substantial caffeine use for a minimum of 6 hours prior to bedtime.
The sleep disruptive effects of caffeine administration at bedtime are well documented.17 Indeed, caffeine administration has been used as a model of insomnia.18 Dose-response studies demonstrate that increasing doses of caffeine administered at or near bedtime are associated with significant sleep disturbance.19–21 One of the most common recommendations for appropriate sleep hygiene practices is to avoid caffeine close to bedtime. However, evidence is less clear regarding the consumption of caffeine