A circadian-informed lighting intervention accelerates circadian adjustment to a night work schedule in a submarine lighting environment

Abstract

Study objective: Night work has detrimental impacts on sleep and performance, primarily due to misalignment between sleep-wake schedules and underlying circadian rhythms. This study tested whether circadian-informed lighting accelerated circadian phase delay, and thus adjustment to night work, compared to blue-depleted standard lighting under simulated submariner work conditions.

Methods: Nineteen healthy sleepers (12 males; mean ± SD aged 29 ± 10 years) participated in two separate 8-day visits approximately 1 month apart to receive, in random order, circadian-informed lighting (blue-enriched and dim, blue-depleted lighting at specific times) and standard lighting (dim, blue-depleted lighting). After an adaptation night (day 1), salivary dim-light melatonin onset (DLMO) assessment was undertaken from 18:00 to 02:00 on days 2-3. During days 3-7, participants completed simulated night work from 00:00 to 08:00 and a sleep period from 10:00 to 19:00. Post-condition DLMO assessment occurred from 21:00 to 13:00 on days 7-8. Ingestible capsules continuously sampled temperature to estimate daily core body temperature minimum (Tmin) time. Tmin and DLMO circadian delays were compared between conditions using mixed effects models.

Results: There were significant condition-by-day interactions in Tmin and DLMO delays (both p < .001). After four simulated night shifts, circadian-informed lighting produced a mean [95% CI] 5.6 [3.0 to 8.2] hours greater delay in Tmin timing and a 4.2 [3.0 to 5.5] hours greater delay in DLMO timing compared to standard lighting.

Conclusions: Circadian-informed lighting accelerates adjustment to shiftwork in a simulated submariner work environment. Circadian lighting interventions warrant consideration in any dimly lit and blue-depleted work environments where circadian adjustment is relevant to help enhance human performance, safety, and health.

Keywords: circadian rhythm; core body temperature; light; melatonin; night work; sleep; submarine.