The impact of a week of simulated night work on sleep, circadian phase, and performance

Abstract

Aims: To investigate factors that may contribute to performance adaptation during permanent night work. Methods: Fifteen healthy subjects participated in an adaptation and baseline night sleep, directly followed by seven simulated eight-hour night shifts (2300 to 0700 hours). At the end of each shift they were taken outside and exposed to natural light for 20 minutes. They then slept from approximately 0800 hours until they naturally awoke.Results: There was a significant increase in mean performance on a visual psychomotor vigilance task across the week. Daytime sleep quality and quantity were not negatively affected. Total sleep time (TST) for each of the daytime sleeps was reduced, resulting in an average cumulative sleep debt of 3.53 hours prior to the final night shift. TST for each of the daytime sleep periods did not significantly differ from the baseline night, nor did TST significantly vary across the week. There was a significant decrease in wake time after sleep onset and sleep onset latency across the week; sleep efficiency showed a trend towards greater efficiency across the consecutive daytime sleeps. Hours of wakefulness prior to each simulated night shift significantly varied across the week. The melatonin profile significantly shifted across the week. Conclusions: Results suggest that under optimal conditions, the sleep debt that accumulates during consecutive night shifts is relatively small and does not exacerbate decrements in night-time performance resulting from other factors. When sleep loss is minimised, adaptation of performance during consecutive night shifts can occur in conjunction with circadian adaptation.

Changes in the Concentration of Urinary 6-sulphatoxymelatonin during a Week of Simulated Night Work

“…The results indicate that the concentration of aMT6s in urine during daytime sleep periods increased throughout the week, which suggests that participants gradually adapted to the day-sleep/night-work schedule. This suggestion is supported by previously published data for these participants showing that salivary melatonin onset occurred progressively later, and neurobehavioural performance during night shifts progressively improved, over the course of the week 5,6) . While the current data indicate that people may adapt to a pattern of work that includes several consecutive night shifts, two particular aspects of the protocol suggest that some caution should be taken in generalising these results to shiftworkers in their natural sleep and work settings.…”

“…As part of this process, our group undertook a laboratory-based study to consider the adaptation of participants to a simulated shiftwork schedule that included seven consecutive 8-h night shifts. Data regarding the neurobehavioural performance, salivary melatonin onset, and quantity/quality of sleep for participants in this protocol have been published elsewhere 5,6) . The aim of the current paper was to examine the adaptation of participants to this night work schedule using the principal metabolite of melatonin in urine-6-sulphatoxymelatonin (aMT6s)-as the circadian phase marker.…”

What Keeps Us Awake?—the Role of Clocks and Hourglasses, Light, and Melatonin

“…With respect to shift work, it is unambiguous that the circadian misalignment between the endogenous circadian signal and the imposed rest-activity cycle is one of the main sources of sleep, performance, and health troubles in night-shift work ers (Lamond et al, 2003). Timed bright light exposure during night work can reduce circadian misalignment in night workers.…”

Association of salivary cortisol with chronomics of 24 hours ambulatory blood pressure/heart rate among night shift workers

“…Among healthy subjects, sleep tends to occur during a particular phase of the circadian cycle (2). Those who work during the night shift may attempt to sleep when their body clock is adjusted for the awakening phase (3). This attempt disturbs the body clock resulting in a contradictory relationship between sleep time and circadian schedule.…”