0015 A circadian-informed lighting intervention markedly accelerates circadian adjustment to a night shift-work schedule

Abstract

Abstract Introduction Night shift-work results in misalignment between circadian timing and the sleep/wake schedule, negatively impacting sleep and performance. In encapsulated environments (e.g., submarines), the lack of strong daily solar lighting cues may impair circadian entrainment to the night shift-work schedule. This study designed and tested a circadian-informed lighting strategy to promote faster circadian phase delays to adjust to night shift-work compared to standard lighting. Methods Nineteen healthy sleepers (12 males/7 females, mean±SD aged 28.7±10.4 years) underwent two separate 8-day experimental conditions (circadian-informed lighting versus standard lighting). After a baseline sleep from 22:00 – 07:00 (day 1) and salivary dim light melatonin onset assessment ([DLMO], day 2), participants undertook simulated night shift-work (00:00 - 08:00) and slept during the day (10:00 - 19:00) for days 3-7 followed by a post-DLMO assessment on day 8. Ingestible capsules collected core body temperature (CBT) continuously throughout days 2-8, and cosine curve fitting was applied to estimate the timing of each daily temperature minima. The standard lighting condition mimicked current lighting on submarines (largely dim, blue-depleted light), while the circadian-informed lighting administered bright, blue-enriched and dim, blue-depleted lighting at times estimated to facilitate rapid circadian delay. The magnitude of daily CBT minima changes and the delay in pre- vs. post-DLMO were compared across conditions. Results There were significant day-by-condition interactions on CBT minima timing and DLMO timing (both p< 0.001). After 4 days of simulated night-shift work there was a mean [95%CI] 4.5 [3.4 to 5.7] hour greater delay in CBT minima and a 4.6 [3.6 to 5.6] hour greater delay in DLMO timing compared to standard lighting, equating to 3.6 and 2.4-fold faster delays in DLMO and CBT minima timing shifts, respectively. Conclusion Circadian-informed lighting substantially accelerates circadian re-adjustment to night shift-work. Lighting interventions could usefully improve sleep, performance, and safety in shift-workers. Support (if any) This research is supported by the Commonwealth of Australia as represented by the Defence Science and Technology Group of the Department of Defence through the Research Network for Undersea Decision Superiority (research agreement number: 9334), with additional financial support from Flinders University and lighting provision support from REDARC.