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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Date results information initially provided
Type of registration
Retrospectively registered

Titles & IDs
Public title
The effects of a scheduled nap during the night shift on sleepiness and cognition in hospital nurses
Scientific title
The effects of a scheduled nap during the night shift on sleepiness and cognitive functioning in female hospital nurses
Secondary ID [1] 296507 0
Nil known
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Sleepiness 310284 0
Cognitive performance decline 310285 0
Neurological 310404 0
Condition category
Condition code
Public Health 309022 309022 0 0
Health service research
Neurological 309119 309119 0 0
Other neurological disorders

Study type
Description of intervention(s) / exposure
Sleepiness and cognitive performance were compared with and without a 30-minute nap scheduled at 4:00 a.m. during the 8-hour night shift (23:00-07:00). All participants were tested on two nights with and two nights without a nap. Maximum two consecutive nights were allowed, all participants completed 4 study nights within 2 weeks period. To minimize the effect of order, participants were randomly assigned to five order groups: (1) nap/no-nap/nap/no-nap, (2) no-nap/nap/no-nap/nap, (3) nap/no-nap/no-nap/nap, (4) no-nap/nap/nap/no-nap, and (5) no-nap/no-nap/nap/nap. During the night shifts, participants reported hourly on sleepiness and performed two cognitive tests, the Letter Cancellation Task (LCT) and the Digit Symbol Substitution Task (DSST), at 3:00 and 7:00 a.m. On nights with a scheduled nap, participants were instructed to retire to a dark and quiet room for 40 minutes at 4:00 a.m. (corresponding to the nadir of circadian alertness, Borbély, 1982), to allow for an approximately 30-minute nap and an additional 10 minutes both to settle down before and to recover after the nap. On no-nap nights they continued their work as usual. To monitor sleep duration and time awake since last sleep, participants wore an actigraph 24 hours before and during the night shift. At the end of each night shift, workload, unusual events (if any occurred), and number of caffeinated beverages consumed were recorded and perceptual nap efficiency was assessed. Participants completed a sociodemographic questionnaire, the Munich ChronoType Questionnaire for Shiftwork (MCTQShift), Pittsburgh Sleep Quality Index (PSQI), and Pre-Sleep Arousal Scale (PSAS) between shifts. Study research assistants were on site to ensure adherence to the nap protocol and completion of the performance tests and study questionnaires.
Intervention code [1] 312821 0
Comparator / control treatment
The participants act as their own control on no-nap nights.
Control group

Primary outcome [1] 307980 0
Levels of sleepiness measured by Karolinska Sleepiness Scale after the nap scheduled at 4 am in comparison to no-nap condition
Timepoint [1] 307980 0
At 5 am, 6 am and 7 am.
Primary outcome [2] 307981 0
The magnitude of change score of number of correct answers on Digit Symbol Substitution Task (DSST) before and after the nap (Delta 3-7) in nap compared to no-nap condition
Timepoint [2] 307981 0
DSST was performed at 3 am (before the nap) and at 7 am (after the nap)
Primary outcome [3] 307983 0
The magnitude of change score of Letter Cancellation Task (LCT) capacity and omission errors before and after the nap (Delta 3-7) in nap compared to no-nap condition
Timepoint [3] 307983 0
LCT was performed at 3 am (before the nap) and at 7 am (after the nap)
Secondary outcome [1] 353562 0
Timepoint [1] 353562 0

Key inclusion criteria
Working at least 75% of full time (28 hours per week) and at least one night shift per week.
Minimum age
20 Years
Maximum age
65 Years
Can healthy volunteers participate?
Key exclusion criteria
Pregnancy, a diagnosed sleep disorder, or chronic medical conditions that may affect sleep and/or function

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Allocation is not concealed
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Simple randomization using a randomization table created by computer software
Masking / blinding
Open (masking not used)
Who is / are masked / blinded?

Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
A one-way ANOVA was performed to compare sleep (SMIN, TA, NAP) and control variables (workload, unusual events, and caffeine consumption) by study nights. DSST and LCT performance between 3:00 a.m. and 7:00 a.m. sessions and between two nap/no-nap night shifts was compared using paired-sample t-tests. Differences in DSST correct responses, LCT capacity, and LCT omission errors between 3:00 a.m. and 7:00 a.m. on nap and no-nap conditions were examined via mixed-model analyses controlling for caffeine consumption, workload, and unusual events. Repeated measures analysis of variance (RM-ANOVA) was used to assess sleepiness throughout the night shift and to compare sleepiness after the nap (at 5:00, 6:00, and 7:00 a.m.) in nap and no-nap conditions. Mixed-model analyses, controlling for age, workload, unusual events, and caffeine consumption, tested the contributions of a nap, biopsychosocial factors, and Nap × Biopsychosocial interactions to sleepiness, DSST, and LCT performance measures.

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment outside Australia
Country [1] 20987 0
State/province [1] 20987 0

Funding & Sponsors
Funding source category [1] 301096 0
Government body
Name [1] 301096 0
Israel Ministry of Economy and Industry
Address [1] 301096 0
5 Bank Israel Street, Jerusalem
Zip code: 9195021
Country [1] 301096 0
Primary sponsor type
University of Haifa
199 Aba Khoushy Ave, Mount Carmel, Haifa
Zip code: 3498838
Secondary sponsor category [1] 300704 0
Name [1] 300704 0
Address [1] 300704 0
Country [1] 300704 0

Ethics approval
Ethics application status
Ethics committee name [1] 301847 0
Western Galilee Medical Center IRB
Ethics committee address [1] 301847 0
POB 21 Naharya
Zip code 22100
Ethics committee country [1] 301847 0
Date submitted for ethics approval [1] 301847 0
Approval date [1] 301847 0
Ethics approval number [1] 301847 0
0056–13 NHR

Brief summary
The present study aimed to examine the effectiveness of a scheduled nap during the nadir of alertness (4 am) on subsequent sleepiness and performance and its interaction with individual factors on sleepiness and cognition during an 8-hour night shift. We hypothesized that a scheduled nap reduces sleepiness and improves cognitive performance in female nurses working night shifts in comparison to no-nap condition and that the benefits of the nap may differ based on individual differences such as age, chronotype, prior sleep duration, time awake, sleep quality, pre-sleep arousal, and number of children in the home.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 88306 0
Prof Tamar Shochat
Address 88306 0
University of Haifa 199 Aba Khoushy Ave. Mount Carmel, Haifa Israel Zip code: 3498838
Country 88306 0
Phone 88306 0
Fax 88306 0
Email 88306 0
Contact person for public queries
Name 88307 0
Mrs Nataly Zion
Address 88307 0
University of Haifa 199 Aba Khoushy Ave. Mount Carmel, Haifa Israel Zip code: 3498838
Country 88307 0
Phone 88307 0
Fax 88307 0
Email 88307 0
Contact person for scientific queries
Name 88308 0
Prof Tamar Shochat
Address 88308 0
University of Haifa 199 Aba Khoushy Ave. Mount Carmel, Haifa Israel Zip code: 3498838
Country 88308 0
Phone 88308 0
Fax 88308 0
Email 88308 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No/undecided IPD sharing reason/comment
Per the IRB's at Bnei Zion Medical Center and Western Galilee Medical Center, data is not to be shared with third parties. However, should a third party be interested, we will consult with IRB.
What supporting documents are/will be available?
No other documents available
Summary results
Have study results been published in a peer-reviewed journal?
Other publications
Have study results been made publicly available in another format?
Other publication details
Citation type [1] 103 0
Conference poster
Citation/DOI/link/details [1] 103 0
The effects of a scheduled nap on nurses' health and performance during the night shift.
International Symposium on Shiftwork and Working Time.Bahia, Brazil
November 4-8, 2013
Attachments [1] 103 0
Citation type [2] 104 0
Citation/DOI/link/details [2] 104 0
The Effects of a Scheduled Nap on Self-Reported Sleepiness and Vigor during the Nightshift in Female Nurses Working Rotating 8-Hr Shifts: A Prospective Field Study.
Associated Professional Sleep Societies 29th Annual Meeting. Seattle,Washington
June 2015

Attachments [2] 104 0
Results – plain English summary
The present study aimed to examine the effectiveness of a scheduled nap and its interaction with individual factors on sleepiness and cognition during an 8-hour night shift. All participants were female and had a mean age of 39.0±9.1 years. Mean experience in shift work was 13.6±8.7 years. Most were married (79.8%), with children living in the household (80.7%); the mean number of children of 1.8±1.2. Fifty-six (51.9 %) of the nurses were overweight, and 18.3% were smokers. Participants were predominantly early chronotypes (76.3%). Lower levels of sleepiness were found at 5:00, 6:00, and 7:00 a.m. on nap versus no-nap nights. Increments in performance between 3:00 and 7:00 a.m. were significantly greater on nap versus no-nap nights for DSST correct responses and LCT capacity. No interactions between the nap and any of the individual factors emerged.