Effects of Bright Light Intervention for Adaptation to Night Work: Shift Work Simulation Experiments
Trial Snapshot
- Phase
- Not Applicable
- Status
- Completed
- Sponsor
- University of Bergen
- Enrollment
- 97
- Locations
- 1
- Primary Endpoint
- Circadian phase
Study Overview
Brief 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).
Study Design
- Study Type
- Interventional
- Allocation
- Randomized
- Intervention Model
- Crossover
- Primary Purpose
- Supportive Care
- Masking
- Single (Participant)
Masking Description
Participants will not be given information on the hypotheses/ expected effects from the different interventions (light conditions).
Eligibility Criteria
- Ages
- 19 Years to 30 Years (Adult)
- Sex
- All
- Accepts Healthy Volunteers
- Yes
Inclusion Criteria
- •Participants are physical and mentally healthy (assessed with BMI and 'General Health Questionnaire-12')
- •Participants accept to comply with the protocol (refrain from alcohol, tobacco and coffee, and retain regular bed- and wake-times the week before the simulated night shifts)
Exclusion Criteria
- •Neurological, psychiatric or sleep related disorders ('Bergen Insomnia Scale', 'global sleep assessement questionnaire')
- •Extreme 'morningness-eveningness' type ('Horne Östberg morningness eveningness questionnaire')
- •Use of medication
- •Worked night shifts the last 3 months
- •Travelled through more than two time zones the last 3 months
Arms & Interventions
Light intensity, 1000 lux (4000 K)
Participants will work three consecutive simulated night shifts under full-spectrum LED-light, 1000 lux (4000 Kelvin) administered through standard room lighting.
Intervention: LED-light, 1000 lux (Device)
Light intensity, 100 lux (4000 K)
Participants will work three consecutive simulated night shifts under full-spectrum LED-light, 100 lux (4000 Kelvin) administered through standard room lighting.
Intervention: LED-light, 100 lux (Device)
Colour temperature, 7000 Kelvin
Participants will work three consecutive simulated night shifts under full-spectrum LED-light, 7000 K (200 lux) administered through standard room lighting.
Intervention: LED-light, 7000 K (Device)
Colour temperature, 2500 Kelvin
Participants will work three consecutive simulated night shifts under full-spectrum LED-light, 2500 K (200 lux) administered through standard room lighting.
Intervention: LED-light, 2500 K (Device)
Blue light, 455 nm
Participants work one night shift with blue LED-light (peak wavelength 455 nm) administered through standard room lighting.
Intervention: Blue LED-light (Device)
Red light, 615 nm
Participants work one night shift with red LED-light (peak wavelength 615 nm) administered through standard room lighting.
Intervention: Red LED-light (Device)
Outcomes
Primary Outcomes
Circadian phase
Time Frame: 5 days-nights
Circadian phase will be measured through assessement of 'Dim Light Melatonin Onset' (DLMO). Saliva samples will be collected every hour in the evening (from 7 pm) to one hour past regular bedtime, one day before the first night shift and the day after the night shift period. Saliva will be analyzed for melatonin, giving an estimate on DLMO.
Sleep
Time Frame: 9 days-nights
Sleep will be measured objectively using actigraphy
Cognitive performance
Time Frame: 3 nights
Cognitive performance will be measured using the Psychomotor Vigilance Test (PVT). The PVT measures sustained attention, and is considered the 'gold standard' for assessing the effects of sleep deprivation on cognition. The task will be performed approx. every 1.5h throughout the nightshifts.
Secondary Outcomes
- Heart rate variability(3 nights)
- Core body temperature(1-2 nights)
- Experiences of perceptual anomalies(3 nights)
- Self-reported sleep(9 days-nights)
- Interleukin(3 nights)
- Granulocyte macrophage colony-stimulating factor (GM-CSF)(3 nights)
- Headache and eyestrain(3 nights)
- Decision/ response execution(3 nights)
- Decision/ response inhibition(3 nights)
- Moral reasoning(3 nights)
- Leadership evaluation(2 nights, 1 day)
- Pain sensitivity(3 nights)
- Working memory(3 nights)
- Cognitive throughput(3 nights)
- Fine motor skills(3 nights)
- Recognition of emotions(3 nights)
- Objective sleepiness, sleep and sleep stages(3 nights and sleep periods)
- Subjective sleepiness(3 nights)
- Interferon gamma (IFN-gamma)(3 nights)
- Tumor necrosis factor alpha (TNF-a)(3 nights)
- Positive and negative affect(3 nights)
- Appetite/ food cravings(3 nights)
- Cognitive control(3 nights)
- Planning(3 nights)
- Pupil size(3 nights)