Sleep-related accidents often involve healthy young persons who are driving at night. Coffee and napping restore alertness, but no study has compared their effects on real nighttime driving performances. To test the effects of 125 mL of coffee (half a cup) containing 200 mg of caffeine, placebo (decaffeinated coffee containing 15 mg of caffeine), or a 30-minute nap (at 1:00 a.m.) in a car on nighttime driving performance. Double-blind, randomized, crossover study. Sleep laboratory and open highway. 12 young men (mean age, 21.3 years [SD, 1.8]). Self-rated fatigue and sleepiness, inappropriate line crossings from video recordings during highway driving, and polysomnographic recordings during the nap and subsequent sleep. Participants drove 200 km (125 miles) between 6:00 p.m. and 7:30 p.m. (daytime reference condition) or between 2:00 a.m. and 3:30 a.m. (coffee, decaffeinated coffee, or nap condition). After intervention, participants returned to the laboratory to sleep. Nighttime driving performance was similar to daytime performance (0 to 1 line crossing) for 75% of participants after coffee (0 or 1 line crossing), for 66% after the nap (P = 0.66 vs. coffee), and for only 13% after placebo (P = 0.041 vs. nap; P = 0.014 vs. coffee). The incidence rate ratios for having a line crossing after placebo were 3.7 (95% CI, 1.2 to 11.0; P = 0.001) compared with coffee and 2.9 (CI, 1.7 to 5.1; P = 0.021) compared with nap. A statistically significant interindividual variability was observed in response to sleep deprivation and countermeasures. Sleep latencies and efficiency during sleep after nighttime driving were similar in the 3 conditions. Only 1 dose of coffee and 1 nap duration were tested. Effects may differ in other patient or age groups. Drinking coffee or napping at night statistically significantly reduces driving impairment without altering subsequent sleep.

As suggested by the authors, the Horne and Ostberg morning/evening questionnaire (MEQ) has never been adapted to evaluate a nonstudent population. The purpose of this study was to validate this MEQ in a sample of middle-aged workers by modifying only the cutoffs. It was administered in 566 non-shift-workers aged 51.2 to 3.2 years who presented no sleep disorders. According to the Horne and Ostberg classification, the sample consisted of 62.1% morning type, 36.6% neither type, and 2.2% evening type. Multiple correspondence analysis, which determines the principal components, was performed on all MEQ items. Then an ascending hierarchical classification was applied to determine 3 clusters from these principal components. On the basis of these 3 clusters, new cutoffs were determined: evening types were considered as scoring under 53 and morning types above 64, thus giving 28.1% morning type, 51.7% neither type, and 20.2% evening type. As an external validation, eveningness was associated with later bedtime and waking-up time (more pronounced at the weekend), greater need for sleep, larger daily sleep debt, greater morning sleepiness, and ease of returning to sleep in the early morning. A positive correlation between age and morningness was again found. This study confirms that “owls” are not rare in a middle-aged sample. We conclude that this adapted MEQ could be useful when investigating age-related changes in sleep.

Summary: The purpose of this study was to determine, in a large sample of adults of all ages (17–80 years), the effect of morningness/eveningness on sleep/wake schedules, sleep needs, sleep hygiene and subjective daytime somnolence. A total of 617 subjects (219 subjects per chronotype group) matched for age, sex and employment status, completed an abridged morningness/eveningness questionnaire, a questionnaire on sleep habits and the quality of sleep, and the Epworth Sleepiness Scale. Eveningness was associated with a greater need for sleep, less time in bed during the week compared to ideal sleep needs, more time in bed at the weekend, a later bedtime and waking‐up time especially at the weekend, more irregular sleep/wake habits and greater caffeine consumption. These subjects built up a sleep debt during the week and extended their duration of sleep at the weekend. They did not, however, rate themselves more sleepy than other types, despite the fact that our results showed a clear link between subjectively evaluated daytime somnolence and sleep debt. Why they were less affected by sleep deprivation is not clear. This raises the question of individual susceptibility to the modification of sleep parameters.

To determine whether real-life driving would produce different effects from those obtained in a driving simulator on fatigue, performances and sleepiness. Cross-over study involving real driving (1200 km) or simulated driving after controlled habitual sleep (8 hours) or restricted sleep (2 hours). Sleep laboratory and open French Highway. Twelve healthy men (mean age ± SD = 21.1 ± 1.6 years, range 19–24 years, mean yearly driving distance ± SD = 6563 ± 1950 miles) free of sleep disorders. Self-rated fatigue and sleepiness, simple reaction time before and after each session, number of inappropriate line crossings from the driving simulator and from video-recordings of real driving. Line crossings were more frequent in the driving simulator than in real driving (P < .001) and were increased by sleep deprivation in both conditions. Reaction times (10% slowest) were slower during simulated driving (P = .004) and sleep deprivation (P = .004). Subjects had higher sleepiness scores in the driving simulator (P = .016) and in the sleep restricted condition (P = .001). Fatigue increased over time (P = .011) and with sleep deprivation (P = .000) but was similar in both driving conditions. Fatigue can be equally studied in real and simulated environments but reaction time and self-evaluation of sleepiness are more affected in a simulated environment. Real driving and driving simulators are comparable for measuring line crossings but the effects are of higher amplitude in the simulated condition. Driving simulator may need to be calibrated against real driving in various condition.