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Trial registered on ANZCTR


Registration number
ACTRN12623000690651
Ethics application status
Approved
Date submitted
24/05/2023
Date registered
28/06/2023
Date last updated
28/06/2023
Date data sharing statement initially provided
28/06/2023
Type of registration
Retrospectively registered

Titles & IDs
Public title
The impact of light intensity during night shifts on circadian adaptation, daytime sleep, and night-time alertness in healthy adults.
Scientific title
The impact of light intensity during night shifts on circadian adaptation, daytime sleep, and night-time alertness in healthy adults.
Secondary ID [1] 309710 0
Nil known
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Circadian misalignment 330090 0
Condition category
Condition code
Mental Health 326985 326985 0 0
Studies of normal psychology, cognitive function and behaviour

Intervention/exposure
Study type
Interventional
Description of intervention(s) / exposure
The study will be conducted at the Sleep and Circadian Rhythms Laboratory at the Appleton Institute. This study will employ a between-groups design with three conditions. Each condition will include a simulated shiftwork protocol with 14 x 12-h night shifts (18:00-6:00) and an 8-h sleep opportunity each day (08:00-16:00). The light conditions during night shifts are: Dim Light (10 lux); Moderate Light (100 lux), or Normal Light (350 lux). The light conditions will be delivered using automated, broad-spectrum, ceiling-mounted LEDs (i.e., warm light).

With the exception of light intensity during night shifts, the 16-day protocol will be the same for all three conditions:
• Night 1. Participants will have an 8-h sleep to adapt to sleeping in the accommodation suite.
• Day 1. Participants will be trained on all test battery tasks to minimise learning effects.
• Night 2. Participants will have an 8-h sleep to establish baseline sleep parameters.
• Day 2. Participants will have a 1-h sleep in the afternoon to assist the transition to night shifts.
• Nights 3–16. Participants will work 14 x 12-h night shifts. During night shifts, participants will complete a 30-min test battery every 2 h to assess cognitive function and self-perceived capacity. Driving will be assessed before and after night shifts with a 20-min ‘commute’ in a driving simulator.
• Days 3–16. Participants will have an 8-h sleep during 12-h breaks between night shifts.
• Participants’ compliance with the protocol was monitored by research staff either in person or via a closed-circuit television system.

All sleep periods will be monitored using polysomnography (PSG). Prior to sleep, a montage of PSG electrodes will be attached to the head and face. PSG data will be assessed in 30-second epochs using standard scoring criteria.

The 30-min test battery will include tasks such as the Addition/Subtraction Task, Digit Symbol Substitution Test, Probed Recall Memory Test, Psychomotor Vigilance Task, etc. Subjective capacity will be assessed using visual analogue scales (e.g., fatigue, sleepiness, mood, alertness, etc).

Body clock time will be assessed using the timing of the daily minimum in core body temperature (CBTmin), sampled in 1-min epochs throughout the protocol using ingestible capsules.

Body clock adaptation will be assessed by collecting urine samples during and after sleep periods and expressing the amount of 6-sulphatoxymelatonin excreted during each daytime sleep period as a percentage of the amount excreted during the night-time baseline sleep period. Over the week of night work, percentages that are closer to 100 will indicate a greater degree of adaptation in participants’ body clocks.
Intervention code [1] 326147 0
Treatment: Other
Comparator / control treatment
Normal light Intensity
Control group
Active

Outcomes
Primary outcome [1] 334825 0
Change in body clock time as measured using urinary 6-sulphatoxymelatonin
Timepoint [1] 334825 0
Body clock adaptation will be assessed by collecting urine samples during and after sleep periods and expressing the amount of 6-sulphatoxymelatonin excreted during each daytime sleep period as a percentage of the amount excreted during the night-time baseline sleep period. Percentages that are closer to 100 will indicate a greater degree of adaptation in participants’ body clocks.
Secondary outcome [1] 422189 0
Change in quantity of daytime sleep assessed using polysomnography
Timepoint [1] 422189 0
Sleep quantity will be assessed using polysomnography each day during the 16-day protocol.
Secondary outcome [2] 422190 0
Change in night-time alertness as measured using a 10-min response time task.
Timepoint [2] 422190 0
Alertness will be measured during a 10-min response time task. The task will be performed 7 times during each 12-h simulated night shift - i.e., 14 simulated 12-h night shifts x 7 times per night shift.
Secondary outcome [3] 423445 0
Change in quality of daytime sleep assessed using polysomnography
Timepoint [3] 423445 0
Sleep quality will be assessed using polysomnography each day during the 16-day protocol.

Eligibility
Key inclusion criteria
Healthy males and females who have a regular sleep pattern.
Minimum age
18 Years
Maximum age
35 Years
Sex
Both males and females
Can healthy volunteers participate?
Yes
Key exclusion criteria
Individuals who smoke, have undertaken transmeridian travel in the 3 months prior to the study, those who suffer from, or have been diagnosed with, a sleep disorder such as sleep apnea, insomnia or narcolepsy, those who undertake shift work, and those who take any form of sleep medication or supplements known to affect sleep (such as melatonin) will be excluded from the study. Individuals who use illicit drugs are also not eligible to participate in the study.

Study design
Purpose of the study
Treatment
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
The person who determined if a participant was eligible for inclusion in the trial was unaware, when this decision was made, to which group the participant would be allocated. Central randomisation by computer was used as the method of allocation concealment.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Permuted block randomisation was used as the method of sequence generation.
Masking / blinding
Open (masking not used)
Who is / are masked / blinded?



Intervention assignment
Parallel
Other design features
Phase
Not Applicable
Type of endpoint/s
Efficacy
Statistical methods / analysis
The study will have a total of 60 participants. The primary hypothesis (i.e., body clock time will get progressively later with each successive night shift, and the daily rate of delay will be smallest (or absent) in dim light and greatest in normal light) will be assessed using separate mixed-design ANOVAs. Each DV’s ANOVA will have one between-subjects factor, i.e., light condition (dim, moderate, normal) and one within-subjects factor, i.e., day of study (baseline, day 3–16).

There are no comparative data available regarding a ‘condition’ x ‘day’ interaction for circadian phase, but if we conservatively assume a small–moderate partial eta squared of 0.02 with a resultant effect size (f) of 0.14, then 18 participants are required in each of the three conditions for the study to have 80% power [1]. We will recruit 20 participants for each condition, i.e., 60 in total, because they will participate in sets of four, and studies of this kind have an attrition rate of ~10%. If 18 participants complete each condition, we will also have (i) 88% power to detect an effect size (d) of 0.70 for a main effect of ‘day’ for circadian phase (CBTmin: day 1 = 4.87 ± 1.95 h, day 7 = 8.96 ± 6.60 h, d = 0.7 [2]), and (ii) 98% power to detect an effect size (d) of 1.25 for a main effect of ‘condition’ for circadian phase (CBTmin: control day 7 = 8.96 ± 6.60 h, intervention day 7 = 15.52 ± 3.16 h, d = 1.25 [2]).

1. Faul et al (2007). G*Power 3. Behav Res Methods, 39, 175-191
2. Boivin & James (2002). Circadian adaptation to night-shift work by judicious light and darkness exposure. J Biol Rhythms, 17, 556-567.

Recruitment
Recruitment status
Recruiting
Date of first participant enrolment
Anticipated
Actual
18/05/2022
Date of last participant enrolment
Anticipated
31/07/2024
Actual
Date of last data collection
Anticipated
16/08/2024
Actual
Sample size
Target
60
Accrual to date
27
Final
Recruitment in Australia
Recruitment state(s)
SA
Recruitment postcode(s) [1] 40410 0
5034 - Wayville

Funding & Sponsors
Funding source category [1] 313903 0
Government body
Name [1] 313903 0
Australian Research Council
Country [1] 313903 0
Australia
Primary sponsor type
University
Name
CQUniversity
Address
Bruce Highway
North Rockhampton Qld 4702
Country
Australia
Secondary sponsor category [1] 315757 0
None
Name [1] 315757 0
Address [1] 315757 0
Country [1] 315757 0

Ethics approval
Ethics application status
Approved
Ethics committee name [1] 313049 0
Human Research Ethics Committee CQUniversity
Ethics committee address [1] 313049 0
Building 32, Bruce Highway
Rockhampton 4702
Ethics committee country [1] 313049 0
Australia
Date submitted for ethics approval [1] 313049 0
22/06/2020
Approval date [1] 313049 0
30/06/2020
Ethics approval number [1] 313049 0
0000022196

Summary
Brief summary
The current evidence suggests that the optimal length of a sequence of night shifts may depend on the intensity of light that shiftworkers are exposed to during the night. If so, then OHS guidelines that recommend a blanket limit on night shifts of a maximum of 2-4 in a row may inadvertently expose shiftworkers to a higher level of fatigue-related risk than is necessary in some workplaces.

In this project, we will test the proposition that shorter sequences of night shifts may be suited to workplaces where shiftworkers operate in dim light and are less likely to adapt to a nocturnal schedule, whereas longer sequences of night shift may be suited to workplaces where shiftworkers operate in normal indoor light and may be more likely to adapt to a nocturnal schedule.

The project will include a multiple-day night work simulation study with three conditions. The only difference between conditions will be in the light intensity during night shifts – dim (10 lux), moderate (100 lux), and normal (350 lux) – as experienced by truck drivers, hospital-based healthcare practitioners, and control room operators, respectively.

The data will be used to test three hypotheses:
1. Body clock time will get progressively later, i.e., delay, with each successive night shift, and the daily rate of delay will be smallest (or absent) in the dim light condition and greatest in the normal light condition.
2. The quantity/quality of daytime sleep will progressively increase with each successive night shift, and the daily increases will be smallest (or absent) in the dim light condition and greatest in the normal light condition.
3. Night-time alertness will decline with each successive night shift in the dim light condition, remain stable in the moderate light condition, and increase with each successive night shift in the normal light condition.
Trial website
Trial related presentations / publications
Public notes

Contacts
Principal investigator
Name 126814 0
A/Prof Charli Sargent
Address 126814 0
CQUniversity
44 Greenhill Road
Wayville
South Australia 5034
Country 126814 0
Australia
Phone 126814 0
+61 8 83784516
Fax 126814 0
Email 126814 0
charli.sargent@cqu.edu.au
Contact person for public queries
Name 126815 0
Prof Gregory D Roach
Address 126815 0
CQUniversity
44 Greenhill Road
Wayville
South Australia 5034
Country 126815 0
Australia
Phone 126815 0
+61 8 83784510
Fax 126815 0
Email 126815 0
greg.roach@cqu.edu.au
Contact person for scientific queries
Name 126816 0
Prof Gregory D Roach
Address 126816 0
CQUniversity
44 Greenhill Road
Wayville
South Australia 5034
Country 126816 0
Australia
Phone 126816 0
+61 8 83784510
Fax 126816 0
Email 126816 0
greg.roach@cqu.edu.au

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
Yes
What data in particular will be shared?
After de-identification, the individual participant data underlying published results only.
When will data be available (start and end dates)?
Immediately following publication, no end date.
Available to whom?
Anyone who wishes to access it
Available for what types of analyses?
Any purpose
How or where can data be obtained?
Access subject will be subject to approvals by Principal Investigator and Associate Investigators:
A/Prof Charli Sargent (charli.sargent@cqu.edu.edu)
Prof Greg Roach (greg.roach@cqu.edu.au)


What supporting documents are/will be available?

Doc. No.TypeCitationLinkEmailOther DetailsAttachment
19205Study protocol  charli.sargent@cqu.edu.au
19206Ethical approval  charli.sargent@cqu.edu.au



Results publications and other study-related documents

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