Light Intervention for Adaptation to Night Work

Effects of Bright Light Intervention for Adaptation to Night Work: Shift Work Simulation Experiments

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.

Study Overview

• Status: Completed
• Conditions: Sleep; Sleep Deprivation; Shift-Work Related Sleep Disturbance
• Intervention / Treatment: Device: LED-light, 1000 lux; Device: LED-light, 100 lux; Device: LED-light, 7000 K; Device: LED-light, 2500 K; Device: Blue LED-light; Device: Red LED-light

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 Type: Interventional
• Enrollment (Actual): 97
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Norway
  • Hordaland
    • Bergen, Hordaland, Norway, 5020
      • The faculty of psychology, University of Bergen

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 19 years to 30 years (ADULT)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: All

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: SUPPORTIVE_CARE
• Allocation: RANDOMIZED
• Interventional Model: CROSSOVER
• Masking: SINGLE

Number of Arms

6

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
EXPERIMENTAL: 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.	Device: LED-light, 1000 lux; 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.
ACTIVE_COMPARATOR: 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.	Device: LED-light, 100 lux; 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.
EXPERIMENTAL: 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.	Device: LED-light, 7000 K; 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.
ACTIVE_COMPARATOR: 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.	Device: LED-light, 2500 K; 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.
EXPERIMENTAL: Blue light, 455 nm; Participants work one night shift with blue LED-light (peak wavelength 455 nm) administered through standard room lighting.	Device: Blue LED-light; Blue light with peak wavelength 455 nm. Known to delay the circadian rhythm, suppress melatonin, and increase alertness.
ACTIVE_COMPARATOR: Red light, 615 nm; Participants work one night shift with red LED-light (peak wavelength 615 nm) administered through standard room lighting.	Device: Red LED-light; Red light with peak wavelength 615 nm. Known not to affect the circadian rhythm, melatonin, and alertness.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Cognitive performance	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.	3 nights
Circadian phase	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.	5 days-nights
Sleep	Sleep will be measured objectively using actigraphy	9 days-nights

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Subjective sleepiness	Karolinska Sleepiness Scale (KSS) will be used to assess subjective sleepiness throughout the night shifts. KSS is a likert scale ranging from 1-9, where subjects rate their sleepiness. '1' indicates 'extremely alert', '9' indicates 'very sleepy/fighting sleep'.	3 nights
Self-reported sleep	A sleep diary will be used.	9 days-nights
Heart rate variability	'Heart Rate Variability' will be assessed by using Polar heart rate monitor V800 that will continuously monitor 'HRV' through the night.	3 nights
Interleukin	Blood spot samples will be analyzed for interleukins (IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-13)	3 nights
Granulocyte macrophage colony-stimulating factor (GM-CSF)	Blood-spot samples will be analyzed for GM-CSF.	3 nights
Interferon gamma (IFN-gamma)	Blood-spot samples will be analyzed for IFN-gamma.	3 nights
Tumor necrosis factor alpha (TNF-a)	Blood-spot samples will be analyzed for TNF-a	3 nights
Positive and negative affect	'Positive and Negative Affect Schedule', will be administered to assess mood.	3 nights
Pain sensitivity	By using a handheld pressure algometer, Wagner FPIX Force One, the pressure pain threshold will be measured. The test site will be the trapezius muscle, and the pressure will be increased in steps of 5 N/sec until the participant indicates pain.	3 nights
Headache and eyestrain	A 'Headache and Eyestrain Scale' will be used to get subjective measures on how participants perceive the lighting conditions.	3 nights
Appetite/ food cravings	Appetite/ food cravings for different food types will be assessed using a visual analogue scale to record response to questions like: "How much would you like to eat xxx right now?" A 'Dot-probe test' provides measure of attentional bias towards various food types (pictures)	3 nights
Working memory	A 'Working Memory Scanning Task' measure ability to encode and maintain information in working memory	3 nights
Decision/ response execution	A 'Two-Choice Numerosity Discrimination Task' measure decision criterion and response execution	3 nights
Decision/ response inhibition	A 'Reversal Learning Decision Task' measure ability to adjust choices/ response inhibition	3 nights
Cognitive control	A 'Task Switching-Performance Test' measure cognitive control	3 nights
Planning	The 'Tower of Hanoi Test' measure planning and sequencing abilities	3 nights
Moral reasoning	the 'Defining Issues Test' measure moral reasoning.	3 nights
Cognitive throughput	A 'Digit Symbol Substitution Test' will be used as a measure of cognitive throughput	3 nights
Fine motor skills	The 'grooved pegboard test' assess fine motor skills through the night shifts	3 nights
Recognition of emotions	An 'emotional hexagon test', were participants rate standardized pictures of faces expressing different emotions, measure the ability to discriminate between emotional expressions.	3 nights
Pupil size	Pupil size will be measured, using a tobii eyetracker, three times during night shifts. This can provide an objective measure of sleepiness.	3 nights
Core body temperature	To get a secondary measure of circadian phase, core body temperature will be measured using ingestible temperature capsules.	1-2 nights
Leadership evaluation	The 'Multifactor Leadership Questionnaire' will be used to assess participants leadership preferences. The questionnaire will be administered during daytime and during night shifts.	2 nights, 1 day
Experiences of perceptual anomalies	The Cardiff Anomalous Perceptions Scale (CAPS) questionnaire will be administered after the night shifts to assess experiences of hallucinations and perceptual anomalies during night shifts. The questionnaire consists of 32 items/questions regarding perceptual anomalies, e.g. "Do you ever notice that sounds are much louder than they normally would be?", that are answered with 'yes' or 'no'. Adding up the number of 'yes' answers gives the CAPS Total Score ranging from 0 (low) to 32 (high). For each item endorsed, participants rate the item for distress, intrusiveness and frequency, giving three subscales. The rating for subscales goes from 1 (low) to 5 (high). Nonendorsed items are considered to have a score of 0 on subscales. For each subscale the possible range goes from 0 (low) to 160 (high).	3 nights
Objective sleepiness, sleep and sleep stages	A subgroup of participants (12-16 in each experiment) will be subject to electroencephalography (EEG) during night shifts, and polysomnography (PSG) after night shifts. EEG will provide a measure of electrical activity in the brain during wakefulness, and can provide an objective measure of sleepiness. PSG will be conducted in the sleep period after night shifts, and allow for the scoring of sleep stages. PSG is considered the gold standard for measuring sleep.	3 nights and sleep periods

Collaborators and Investigators

• Sponsor: University of Bergen
• Collaborators: Glamox
• Investigators: Principal Investigator: Erlend Sunde, University of Bergen, Department of Psychosocial Science

Publications and helpful links

General Publications

• Sunde E, Mrdalj J, Pedersen TT, Bjorvatn B, Gronli J, Harris A, Waage S, Pallesen S. Bright light exposure during simulated night work improves cognitive flexibility. Chronobiol Int. 2022 Jul;39(7):948-963. doi: 10.1080/07420528.2022.2050922. Epub 2022 Mar 28.
• Sunde E, Pedersen T, Mrdalj J, Thun E, Gronli J, Harris A, Bjorvatn B, Waage S, Skene DJ, Pallesen S. Alerting and Circadian Effects of Short-Wavelength vs. Long-Wavelength Narrow-Bandwidth Light during a Simulated Night Shift. Clocks Sleep. 2020 Nov 25;2(4):502-522. doi: 10.3390/clockssleep2040037.
• Sunde E, Pedersen T, Mrdalj J, Thun E, Gronli J, Harris A, Bjorvatn B, Waage S, Skene DJ, Pallesen S. Blue-Enriched White Light Improves Performance but Not Subjective Alertness and Circadian Adaptation During Three Consecutive Simulated Night Shifts. Front Psychol. 2020 Aug 18;11:2172. doi: 10.3389/fpsyg.2020.02172. eCollection 2020.
• Sunde E, Mrdalj J, Pedersen T, Thun E, Bjorvatn B, Gronli J, Harris A, Waage S, Pallesen S. Role of nocturnal light intensity on adaptation to three consecutive night shifts: a counterbalanced crossover study. Occup Environ Med. 2020 Apr;77(4):249-255. doi: 10.1136/oemed-2019-106049. Epub 2020 Feb 4.

Study record dates

Study Major Dates

• Study Start (ACTUAL): August 25, 2017
• Primary Completion (ACTUAL): March 27, 2019
• Study Completion (ACTUAL): March 27, 2019

Study Registration Dates

• First Submitted: May 3, 2017
• First Submitted That Met QC Criteria: June 26, 2017
• First Posted (ACTUAL): June 29, 2017

Study Record Updates

• Last Update Posted (ACTUAL): May 16, 2019
• Last Update Submitted That Met QC Criteria: May 15, 2019
• Last Verified: February 1, 2018

More Information

Terms related to this study

• Keywords: sleep; circadian rhythm; cognitive performance; light; shift work; bright light; night work
• Additional Relevant MeSH Terms: Mental Disorders; Nervous System Diseases; Sleep Wake Disorders; Neurologic Manifestations; Dyssomnias; Parasomnias; Sleep Deprivation
• Other Study ID Numbers: 270755

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: After the project has ended the data will be anonymized and no direct recognizable information will be stored.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No