Dynamic lighting schedules to facilitate circadian adaptation to shifted timing of sleep and wake

Abstract

Circadian adaptation to shifted sleep/wake schedules may be facilitated by optimizing the timing, intensity and spectral characteristics of light exposure, which is the principal time cue for mammalian circadian pacemaker, and possibly by strategically timing nonphotic time cues such as exercise. Therefore, circadian phase resetting by light and exercise was assessed in 44 healthy participants (22 females, mean age [±SD] 36.2 ± 9.2 years), who completed 8‐day inpatient experiments simulating night shiftwork, which included either an 8 h advance or 8 h delay in sleep/wake schedules. In the advance protocol (n = 18), schedules were shifted either gradually (1.6 h/day across 5 days) or abruptly (slam shift, 8 h in 1 day and maintained across 5 days). Both advance protocols included a dynamic lighting schedule (DLS) with 6.5 h exposure of blue‐enriched white light (704 melanopic equivalent daylight illuminance [melEDI] lux) during the day and dimmer blue‐depleted light (26 melEDI lux) for 2 h immediately before sleep on the shifted schedule. In the delay protocol (n = 26), schedules were only abruptly delayed but included four different lighting conditions: (1) 8 h continuous room‐light control; (2) 8 h continuous blue‐enriched light; (3) intermittent (7 × 15 min pulses/8 h) blue‐enriched light; (4) 8 h continuous blue‐enriched light plus moderate intensity exercise. In the room‐light control, participants received dimmer white light for 30 min before bedtime, whereas in the other three delay protocols participants received dimmer blue‐depleted light for 30 min before bedtime. Both the slam and gradual advance protocols induced similar shifts in circadian phase (3.28 h ± 0.37 vs. 2.88 h ± 0.31, respectively, p = .43) estimated by the change in the timing of timing of dim light melatonin onset. In the delay protocol, the continuous 8 h blue‐enriched exposure induced significantly larger shifts than the room light control (−6.59 h ± 0.43 vs. −4.74 h ± 0.62, respectively, p = .02). The intermittent exposure induced ~60% of the shift (−3.90 h ± 0.62) compared with 8 h blue‐enriched continuous light with only 25% of the exposure duration. The addition of exercise to the 8 h continuous blue‐enriched light did not result in significantly larger phase shifts (−6.59 h ± 0.43 vs. −6.41 h ± 0.69, p = .80). Collectively, our results demonstrate that, when attempting to adapt to an 8 h overnight work shift, delay shifts are more successful, particularly when accompanied by a DLS with high‐melanopic irradiance light stimulus during wake.

Light as a Modulator of Non-Image-Forming Brain Functions—Positive and Negative Impacts of Increasing Light Availability

“…Another study found dynamic indoor lighting at the workplace during the daytime advances melatonin onset and peripheral heat loss in the evening, which can be beneficial for people with delayed circadian rhythms [ 135 ]. Further, dynamic lighting can be also beneficial for circadian adaptation to shifted sleep–wake schedules [ 136 ]. The respective roles of spectral and illuminance changes cannot be discriminated yet, in terms of the beneficial effects of dynamic light.…”

Adaptive Circadian Rhythms for Autonomous and Biologically Inspired Robot Behavior

“…Circadian rhythms are periodic 24-h variations that control critical biological functions in living beings such as emotion, body temperature, or alertness [ 15 ]. These rhythms are not only a consequence of external conditions since many studies have reported that organisms possess endogenous self-sustained rhythms even in the absence of arousing stimuli [ 3 , 15 , 16 ]. The previous studies reveal the presence of an endogenous circadian rhythm that controls our bodies.…”

“…Since ages, those living beings with better adaptive capabilities have demonstrated more chances to survive and genetically evolve in new generations [ 1 ]. In the XVIII century, Jean Jacques d’Ortous de Mairan [ 2 ] discovered that one of the leading causes of living beings’ adaptation was biological rhythms, periodic variations in their internal state adapted to ambient conditions [ 3 ]. Recent findings [ 4 ] highlight that the suprachiasmatic nucleus (SCN) is the primary pacemaker in humans.…”

Physiological consequences of space flight, including abnormal bone metabolism, space radiation injury, and circadian clock dysregulation: Implications of melatonin use and regulation as a countermeasure

“…Induction of phase advances of the circadian clock should include exposure to dim light/darkness in the evening of the circadian clock period because exposure to bright light in the evening induces a phase delay of the circadian clock. 210,211 The phase advances in the circadian clock promote synchrony between the circadian clock and scheduled sleep-wake cycles in astronauts during space flight (b). Here, endogenous melatonin would increase in astronauts at the beginning of the sleep episode (c), contributing to the onset of sleep episode adjustment to the scheduled sleep-wake cycle of the shuttle mission.…”

“…In particular, the combination of exposure to bright light (~3000 lux) and the administration of a pharmacological dose of melatonin (5 mg) was reported to induce a great phase advance of the human circadian clock on Earth, 209 and can be expected to induce phase advances in astronauts during space flight. Induction of phase advances of the circadian clock should include exposure to dim light/darkness in the evening of the circadian clock period because exposure to bright light in the evening induces a phase delay of the circadian clock 210,211 . The phase advances in the circadian clock promote synchrony between the circadian clock and scheduled sleep–wake cycles in astronauts during space flight (b).…”