Optimising sleep regularity during shiftwork is important for cognitive performance, sleepiness and mood

Abstract

Sleep regularity is important for performance and wellbeing. Sleep regularity is underexplored in shiftworkers, a population that may struggle to maintain regular sleep timing due to unstable work hours. It is important to understand how sleep regularity relates to wellbeing and performance outcomes for shiftworkers. Using the sleep regularity index (SRI), we assessed the relationship of sleep regularity to performance and wellbeing in maritime watchstanding shiftworkers who worked two different schedules (known as “watchbills”). Active-duty sailors (N = 23, aged 25.96 ± 3.13 years, [mean ± standard deviation]) wore an actiwatch for ~14 days while underway on the 5-hrs on/10-hrs off watchbill, and four months later for ~10 days while on the 3-hrs on/9-hrs off watchbill. The psychomotor vigilance task (PVT) was administered 2 to 4 times daily during both underway periods; the Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), and Profile of Mood States (POMS) were administered at the end of both data collection periods. High variability in SRI score was observed for shiftworkers on the same shift of the same schedule. Higher SRI scores were associated with faster reaction times (Spearman’s rho [ρ] = -0.73, p = .019) and better cognitive performance on seven other PVT metrics (all p < .05), and reduced daytime sleepiness (ρ = -0.512, p = .013) and total mood disturbance (ρ = -0.634, p = .005). The study found that sleep regularity is an important dimension of sleep to optimise during shiftwork to improve cognitive performance and reduce daytime sleepiness and mood disturbance.