ABSTRACT
Introduction 14
Sleep 14
Alertness Cycles 15
Motives for Consumption 17
Regular and Irregular Sleep-Wake Schedules 18
Simulated Real-Life Situations 19
Real-Life Work Situations 20
Aids to Caffeine 21
Bright Light 21
Naps 22
Slow-Release Caffeine 23
Methodological Comments 24
Awake or Less Sleepy 25
Measuring Caffeine Intake Assessment: Underreporting 25
Self-Report 25
Sources of Caffeine 26
Subjective and Objective Assessment 26
Expectancy, Instruction, and Placebo 27
Withdrawal Effects 28
Blaming Coffee, the Placebo Effect 29
Discussion and Conclusion 29
References 30
INTRODUCTION
It is a daily observation that in public transport, at home in the evening, and at times when people are expected to be fully awake, they suffer from a continuous sleep deprivation and too low a level of wakefulness. Data from laboratory studies show that a shortage of nocturnal sleep by as little as 1.3 to 1.5 h for one night results in a one third reduction of daytime objective alertness (Bonnet and Arand, 1995). Other studies show that 17 to 57% of healthy young adults have sleep onset latencies (SOL) during daytime of <5.5 min (±50% of the normal SOL) and that about 28% of young adults as a rule sleep less than 6.5 h each night of the week. In general, there exists a significant sleep loss in at least one third of all adults. For this reason it is not amazing that fatigue is a factor in 57% of traffic accidents, resulting in many casualties and an estimated loss of $56 billion in the U.S. alone (Bonnet and Arand, 1995). It is no surprise that people look for ways to compensate for a shortage of sleep and to stay awake when necessary. Caffeine-containing beverages such as coffee might be of help. Unfortunately most studies, especially those conducted before the 1990s, have been focused on disturbing sleep and wakefulness by giving caffeine shortly before sleep. Hence, the conclusion from a review (Snel, 1993) was that caffeine induced a restless sleep, predominantly in the first half of the sleep. Effects of caffeine on sleepiness were assessed mainly by measuring sleep latency, mood, and task performance. With doses of caffeine up to 400 mg, sleep latency increased and task performance improved on easy tasks but tended to be impaired on complex tasks. More recent studies also adhere to the tradition of giving caffeine shortly before going to sleep (Landolt et al., 1994; Lin et al., 1997; Hindmarch et al., 2000) or even administer caffeine (5 mg/kg) intravenously during sleep (Lin et al., 1997). Such studies make it difficult to appraise the influence of coffee on sleep and wakefulness in everyday life.
