Light Intervention for Adaptation to Night Work
Condition: Shift-Work Related Sleep Disturbance; Sleep Deprivation; Sleep
MeSH terms: Dyssomnias; Parasomnias; Sleep Deprivation
Study type: Interventional

Summary: 
      The project will contribute with new knowledge concerning how aspects of the physical work
      environment (lighting conditions) can be arranged to facilitate the workers' adaptation to
      night work. This is important given the reported adverse consequences of shift work for
      performance, safety, and health. The project involves a series of three experimental,
      laboratory based shift work simulation studies. The aim is to investigate how different
      lighting conditions (intensities and colour temperature), administered through light emitting
      diode (LED) based bright light integrated standard room lighting, affects adaptation to three
      consecutive simulated night shifts and re adaptation to a day oriented schedule on measures
      of alertness, cognitive performance, sleep and circadian rhythm. The proposed project
      examines the effects of interventions that can be applied in naturalistic settings and will
      be based on new laboratory infrastructure available at the laboratories situated in the
      Faculty of Psychology, University of Bergen.
    

Detailed description: 
      Bright light has been suggested as a countermeasure to the negative impact of night work in
      terms of safety, performance and subsequent sleep. The effect depends on the timing of light
      (e.g, phase-response curve), duration of light exposure and the intensity of light, as well
      as the wavelengths that are emitted. Exposure to bright light (more intense than typical room
      lightning), at evening and night, has been effective in delaying the circadian rhythm to
      sufficiently adapt to night work both in simulated night work, and in field studies of
      workers. Blue light has significantly stronger phase shifting effects than other wavelengths
      of the visible spectrum. The effect of light on the circadian system is mediated by retinal
      photoresponsive cell population (intrinsically photoresponsive retinal ganglion cells; ipRGC)
      that contains the photopigment melanopsin, highly sensitive to blue light. These cells signal
      directly to the suprachiasmatic nuclei (SCN) of the hypothalamus, the circadian pacemaker.
      Bright light has also been reported to improve alertness and performance during night shifts.

      To the best of the investigators knowledge, no shift work simulation study has made the full
      advance of LED-technology in terms of using light administered via standard room lighting on
      adaptation to night work. Today, new LED-technology represents an excellent opportunity to
      study this as roof mounted LED-sources integrated as standard indoor lightening can be
      programmed to provide a wide range of light intensities and colour temperatures. LED-sources
      have the advantage over standard light therapy that subjects can be exposed to the therapy
      via standard room lightening (not confined to a special therapy lamp) thereby allowing the
      workers to conduct work tasks as normal during light exposure.

      Against this backdrop this project aims to investigate how different lighting conditions,
      administered through LED-based bright light integrated standard room lighting, affects
      adaptation to three consecutive simulated night shifts and re adaptation to a day oriented
      schedule on measures of alertness, cognitive performance, sleep and circadian rhythm. In
      addition, measures of mood, appetite, heart rate variability (HRV), pain sensitivity, moral
      reasoning, and inflammatory markers will be examined. The researchers also aim to investigate
      the effects of two extreme monochromatic light conditions (blue vs. red) based on integrated
      standard room lighting on the adaptation to one simulated night shift.

      Study participants will work simulated night shifts (11:00 pm to 07:00 am) in a light
      laboratory where light parameters (intensity and colour temperature) can be manipulated via
      roof mounted LED-sources integrated as standard indoor lightening. Participants will be
      recruited among students at the University of Bergen, and a screening will be done to ensure
      healthy participants fit for the study. The included participants will take part in
      experiments with two bouts of three consecutive simulated night shifts (6 nights in total).

      HRV will be measured throughout the night shift, and five times, approx. every 1.5 hour
      (11:30 pm, 01:00 am, 02:30 am, 04:00 am, 05:30 am), the subjects will be tested on a test
      battery of cognitive tests and will rate their subjective sleepiness. Sleep will be assessed
      by sleep diary and actigraphy 3 days prior to, during, and 3 days following the shifts. One
      day before the night shift and the day after the night shift period the circadian rhythm will
      be measured by saliva samples for estimation of dim light melatonin onset. Prior to-, during-
      and after the night shifts, participants will undergo a pain sensitivity test. Blood spot
      samples will be collected at the beginning and the end of each night shift for analysis of
      inflammatory markers (e.g. interleukins).
    

Intervention name(s): LED-light, 1000 lux; LED-light, 100 lux; LED-light, 7000 K; LED-light, 2500 K; Blue LED-light; Red LED-light
Intervention type(s): Device; Device; Device; Device; Device; Device
Intervention description(s): Full-spectrum light, 1000 lux, 4000 K. Represent a light intensity within acceptable range (light that is not too glary); 4000 K is among the most commonly used indoor light colour temperatures.; Full-spectrum light, 100 lux, 4000 K. Represent a light intensity within acceptable range (light that provides sufficient eye sight); 4000 K is among the most commonly used indoor light colour temperatures.; Full-spectrum light, 7000 K, 200 lux. Represent the upper border of common colour indoor light temperature, 200 lux is a common indoor light intensity.; Full-spectrum light, 2500 K, 200 lux. Represent the lower border of common colour indoor light temperature, 200 lux is a common indoor light intensity.; Blue light with peak wavelength 455 nm. Known to delay the circadian rhythm, suppress melatonin, and increase alertness.; Red light with peak wavelength 615 nm. Known not to affect the circadian rhythm, melatonin, and alertness.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Three related night shift studies have been planned. Each study investigates how different lighting conditions, administered through LED-based bright light integrated standard room lighting, affects adaptation to simulated night shifts and re adaptation to a day oriented schedule.
In each study, 28 participants (84 in total) will be exposed to the interventions (light conditions) in a randomized, blinded, controlled, crossover study.
The simulated night shifts will last from 11pm to 7am. The specific light conditions will last from 11pm to 5am (study 1: 1000 lux vs. 100 lux; study 2: 7000 K vs. 2500 K; study 3: 455 nm vs. 615 nm) where after (from 5am to 7am) all participants will be exposed to the same light conditions (200 lux, 4000 K). After completion of one bout of night work (three consecutive shifts for study 1 and 2; one night shift for study 3) there will be a washout period of four weeks before the participants cross over.
Masking: Single (Participant)
Primary purpose: Supportive Care
Keywords: night work; shift work; light; bright light; sleep; cognitive performance; circadian rhythm