A life of research on everyday sleep(iness)

Abstract

This is a personal review of a research life focused on sleep in everyday life. It finds that irregular work hours shorten sleep duration and increase sleepiness, both subjectively and objectively (polysomnography). Also, experimental lab studies demonstrate reduced sleep duration (and sleep stages N2 and REM) when sleep is moved into the daylight hours (and the circadian upswing). Stage N3% seems not affected, and homeostatic experiments suggest that awakenings should not occur until the need for N3% or total spectral power has been satisfied. Furthermore, sleepiness is associated with increased alpha activity and slow eye movements, although the best indicator of dangerous sleepiness is subjective ratings (linked to perceptions of heavy eye lids). Everyday stress has very modest negative effects on objective sleep quality. Sleep loss as well as excessive sleep durations are linked to mortality, but with modest risk, and mainly in older individuals. Finally, objective sleep poorly reflects subjective sleep quality, and women appear to report poorer sleep than men, while objective data show better sleep quality in women. The discrepancy is considerably greater in older age groups.

Keywords: age; gender; mortality; shift work; sleep duration; sleep quality; sleepiness; stress.

Figure 1.

Sleep duration after bedtimes at different times of day and ad lib sleep duration. Mean ± se [11].

Figure 2.

Total spectral power remaining to be recovered each hour during daytime sleep [13]. In percent of the total spectral power of night + daytime sleep for the 8 h sleep condition (mean ± se). The last point represents total spectral power remaining upon awakening (dashed line connects to last full hour of sleep).

Figure 3.

Spectral analysis of EEG of one train driver during night driving [27]. The Y-axis represents time and major stations. Asterisks indicate points of nonresponding to traffic signs. Alpha activity increases strongly after an hour’s drive. By permission from Elsevier.

Figure 4.

KSS and the probability of crossing a white line within 5 minutes on a country road during real driving [33].

Figure 5.

Components of the Sleep/Wake Predictor (SWP). A circadian component that is added to a homeostatic component (“S” during wakefulness and “S’” during sleep) to yield S + C = Alertness level. Sleep is terminated when level 15 is reached. Alertness level was later expressed as KSS.

Figure 6.

Mortality (OR, 95% confidence interval) associated with reported sleep duration. Unadjusted and adjusted for age and health. Dotted line = OH for reference value (7 h).