Observational StudyRole of Sleep Reactivity in Shift Work Disorder

Timed bright light exposure will be delivered in a controlled laboratory setting (10,000 lux) designed to delay the DLMO to 4 am or later. This would shift the circadian nadir (e.g., the period of maximal sleepiness) into the typical daytime sleep period after the nightshift (i.e., circadian nadir at \~10am). Bright light will be delivered in a controlled lab environment using a full spectrum light-box with UV filter (Sunbox Sunray II) to achieve a robust reduction of circadian misalignment. The light schedule will be tailored to each individual nightshift worker, determined by: 1) their baseline circadian phase, and 2) the human phase response curve adjusted to the individual's baseline circadian phase.

Shift workers randomized to the control condition will receive less intense light that still has a perceptible alerting effect (100 photopic lux). However, light will occur during a portion of the phase response curve with minimal phase shifts.

The CBT condition will probe sleep reactivity using validated CBT strategies over 6 sessions in accordance with the two-factor theory of emotion. Behavioral strategies will be used to reduce physiological arousal (e.g., relaxation training, breathing) and to strengthen behavioral cues for sleep (e.g., sleep hygiene and sleep scheduling). Sleep times will be scheduled to align with the reduced circadian misalignment (compromised phase position, i.e., maintaining a slightly delayed sleep period on offwork days). Cognitive strategies will identify stressors (e.g., dysfunctional beliefs about sleep) and intervene on worry and rumination with cognitive reappraisal and active coping. Sessions will be conducted by a trained behavioral sleep medicine provider via telemedicine to increase accessibility.

This condition will use an established sleep education control protocol modified for nightshift workers based on the "Plain Language about Shiftwork" published by the National Institute for Occupational Safety and Health (NIOSH). Sleep duration recommendations will be equivalent to the CBT group (8 hours of sleep opportunity) to ensure that outcomes are not confounded by time in bed. Materials in the sleep education control condition will be separated into weekly electronic materials monitored for engagement and completion.

Timed bright light exposure delivered in a controlled laboratory setting (10,000 photopic lux) designed to delay the DLMO to 4 am or later.

Timed less intense light exposure delivered in a controlled laboratory setting (100 photopic lux) that still has a perceptible alerting effect but is not designed to shift circadian phase.

Cognitive strategies will identify stressors (e.g., dysfunctional beliefs about sleep) and intervene on worry and rumination with cognitive reappraisal and active coping. Sessions will be conducted by a trained behavioral sleep medicine provider via telemedicine to increase accessibility.

Sleep duration recommendations will be equivalent to the CBT group (8 hours of sleep opportunity) to ensure that outcomes are not confounded by time in bed. Materials in the sleep education control condition will be separated into weekly electronic materials monitored for engagement and completion.