Using Light to Facilitate Circadian Entrainment from Day to Night Flights

BACKGROUND: As part of a larger project to provide recommendations regarding limitations and best practices for shifting aviators from day to night operations, a study was conducted to assess the efficacy of high energy visible (HEV) light to shift the circadian rhythm in humans. The study attempted to replicate the patterns of military aviators who could be required to shift abruptly from day to night flight operations.METHODS: Simulated flight performance and salivary melatonin levels of 10 U.S. military aviators were collected over a 3-night period using a within-subject dim light melatonin onset (DLMO) study design. Data were collected in a laboratory with participants returning home to sleep following each of the three evenings/nights of data collection. Light treatment included a single 4-h exposure of blue-enriched white light (∼1000 lux) on night 2. Data collected included melatonin levels, light exposure, sleepiness, cognitive workload, and simulated flight performance.RESULTS: The average delay in melatonin onset was 1.32 ± 0.37 h (range: 53 min to 1 h 56 min). Sleepiness (P = 0.044) and cognitive workload (P = 0.081) improved the night following the light treatment compared to the baseline. No systematic differences were identified in flight performance.DISCUSSION: The HEV light treatment successfully delayed the circadian phase of all participants even though participants' ambient light levels (including daylight) outside the laboratory were not controlled. These findings were used to develop circadian synchronization plans for aviators who are asked to transition from day to night operations. These plans will be assessed in a follow-on study in an operational unit.Shattuck NL, Matsangas P, Reily J, McDonough M, Giles KB.