299 Limited Time for Sleep in Night Shift Workers is associated with Risk of Insomnia and Shift Work Disorder

Introduction Sleep deficiency is a severe problem faced by night shift workers. Approximately one-third of night workers report insomnia during daytime sleep and excessive sleepiness during nighttime work; when severe, these symptoms characterize shift work disorder (SWD). Difficulty sustaining 7 to 9 hours of sleep during the daytime is partly due to a circadian drive for wakefulness. Not much is known, however, about how non-work activities contribute to the inability to obtain recovery sleep. We sought to explore how much time night workers are able to allocate for daytime sleep, and how this relates to insomnia-like symptoms and the likelihood of developing SWD. Methods Night shift workers (n=452, 19–69 years old, 54% men) from various occupations who worked at least four night shifts per month completed an online survey. This included questions related to shift duration, hours per workday of non-optional non-work activities, self-rated sleep need, the Insomnia Severity Index (ISI) and a validated 4-item SWD screening questionnaire. For each participant, we calculated the duration of work plus non-optional activities and compared the remaining available time for sleep to their self-described sleep need. Non-parametric Chi-square analyses and Pearson correlations were conducted. Results On average, shift duration was 8.9±1.6 hours, non-optional activities were 3.6±2.9 hours, and sleep need was 7.6±1.6 hours, leaving 15% of shift workers with insufficient free time to obtain the amount of sleep they needed. The percentage of workers at high risk for SWD was significantly greater among those who did not have enough free time for sleep compared to those whose schedules allowed sufficient sleep time (72% vs. 42%; χ2=20.2, p<0.0001). We also found that shift workers with insufficient free time for sleep reported higher insomnia severity (r2=-0.20, p<0.0001). Conclusion About 15% of night workers have non-optional activities outside work that limit their time to obtain sufficient sleep, and this contributes to greater insomnia-like symptoms and increased risk for SWD. Future research should focus on understanding what these non-optional activities are and whether they differ between night and day workers. These insights will enable personalized countermeasures to maximize the sleep and health of shift workers. Support (if any) Supported by US NIH grant R01-AG044416.