Night Work During Midnight Sun and Polar Nights: Impact on Alertness, Sleepiness and Fatigue

Introduction: The circadian clock's sensitivity to light means that seasonal changes in photoperiod can affect circadian entrainment in shift workers, thus influencing their adaptation to night work. At high latitudes, such as the Arctic, extreme daylight variations across seasons, provide a unique context for studying such circadian disruption. Polar nights and midnight sun may further challenge circadian entrainment mechanisms. Whether shift work and seasonal variations cumulate or combine their effect in the photoperiodic zeitgeber remains unclear. This study investigates how seasonal variations may interact with consecutive morning and night shifts to impact alertness, sleepiness and fatigue.