Authors: Line Victoria Moen, Jenny-Anne S Lie, Ingrid Løken Jørgensen, Lars Frøjd, Ståle Pallesen, Dagfinn Matre
Categories: Occupational and Environmental Medicine, SLEEP MEDICINE, Occupational Health Services, Workplace
Source: BMJ Open
Authors: Line Victoria Moen, Jenny-Anne S Lie, Ingrid Løken Jørgensen, Lars Frøjd, Ståle Pallesen, Dagfinn Matre
Shift work is associated with disrupted sleep, circadian misalignment and increased risks of adverse health, performance and safety outcomes. Although recommendations for shift workers typically focus on obtaining one long sleep period, many shift workers divide sleep into two episodes, referred to as biphasic sleep. Biphasic sleep may help mitigate sleep loss-related impairments, yet its prevalence, characteristics and potential benefits for shift working populations remain unclear. Existing reviews have examined sleep duration, mental health, or the consequences of shift work broadly, but none have specifically mapped evidence comparing biphasic and monophasic sleep between shifts. This scoping review will identify and summarise the available literature on biphasic sleep among adult shift workers. In addition, we will describe the outcomes and subsequently highlight any possible gaps to inform future research.
This review will follow the Joanna Briggs Institute methodology for scoping reviews and be reported in accordance with the preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews guidelines. Biphasic sleep is defined as two distinct sleep episodes within a 24-hour period between work shifts, including two similarly timed sleep periods or one longer sleep combined with a shorter nap. A comprehensive search will be conducted in April 2026 in MEDLINE, Embase, PsycINFO, Web of Science and CENTRAL using controlled vocabulary (eg, Medical Subject Headings) and free-text terms related to shift work and split sleep. Peer-reviewed primary research examining biphasic sleep among adult shift workers will be included, and studies focusing solely on naps during work hours will be excluded. Two reviewers will independently screen titles/abstracts and full texts, with discrepancies resolved through discussion or by consulting a third reviewer. Data will be extracted using a standardised template including study characteristics, sleep parameters and reported outcomes. Results will be summarised descriptively and presented in tables and evidence maps. No statistical synthesis will be performed.
This scoping review will synthesise data from articles published in peer-reviewed journals. As no primary data will be collected and no human participants will be involved, the review is exempted from formal ethical approval. Findings will be disseminated in terms of a peer-reviewed publication and will inform future systematic reviews on sleep strategies among shift workers.
This project is registered with the Open Science Framework accessible at 10.17605/OSF.IO/WY7KJ.
Shift work often disrupts normal sleep patterns and can lead to reduced sleep duration, poorer sleep quality and impaired alertness.13 Shift work is further linked to a wide range of adverse health outcomes, including increased risks of cardiovascular disease and mortality,^4 5^ major cardiovascular risk factors,^6 7^ impaired mental health,^8^ weight gain,^9^ breast cancer,^10 11^ prostate cancer,^12^ impaired reproductive health,^13^ dementia,^14^ all-cause mortality^15^ and reduced safety at work.^16 17^ A likely explanation for the aforementioned negative effects of shift work is poor sleep, circadian disruption and risk behaviours/psychosocial stress associated with shift work.^18^
While most sleep recommendations for shift workers focus on obtaining a single, long sleep period, some workers use alternative strategies, such as splitting their sleep into two or more shorter periods, or combining a main sleep period with a shorter nap.1921 Sleeping in two phases can involve a short sleep period (nap) immediately after the shift, followed by a longer sleep period before the next shift. Alternatively, it may consist of two equally long sleep periods, or a longer sleep period right after shift work, followed by a shorter nap before the subsequent shift. In the present paper, we define all abovementioned sleeping patterns as biphasic sleep.
Biphasic sleep reflects both a natural sleep pattern seen across cultures and a potential therapeutic approach for specific populations, such as shift workers.^22^ While the prevalence of biphasic sleep remains largely unknown, a well-known form of biphasic sleep is the siesta, a brief daytime sleep episode that is culturally ingrained in Mediterranean countries. A siesta habit has been associated with cardiometabolic outcomes, including increased obesity risk,^23^ although some benefits have been reported.^24^ In addition, anecdotal reports indicate that attempts to adapt to multiple short sleep episodes are common, particularly among young adults.^25^ Shift workers, and especially those who work at night, are thought to rely on sleep divided into two or more periods more often than non-shift workers, as a strategy to cope with misaligned shift schedules and curtailed sleep. Biphasic sleep is common in limited wake shift work schedules where time at work is more than 8 hours and where there is more than one rest period per day.^26^ Overall, there seems to be emerging evidence that extending or “banking” sleep prior to work shifts can help mitigate fatigue and may lead to improvements in performance, safety and certain health outcomes.^27^
A recent literature review describes the phenomenon of biphasic sleep from a historical and sociological perspective.^22^ In addition, several recently published reviews have examined sleep among shift workers. One of these examined how shift work impacts sleep and mental health among workers and found that the transition to shift work had consistent adverse effects manifested as a reduction of total sleep duration and an increase in symptoms of depression and burnout.^8^ Another review found that night and rotating shift work significantly reduces total sleep time among healthcare workers, though the review primarily focused on the main sleep episode.^28^ Similarly, a review of 15 studies found that sleep duration was consistently insufficient among shift workers, with the early career period being especially vulnerable to reductions in sleep and declines in sleep quality.^29^ Another review concluded that having sleep complaints, including short sleep duration, had more robust associations to worsened mental health among shift workers than non-shift workers.^30^ While 10 min naps are often recommended to enhance daytime performance, this duration appears less effective during night shifts, when extended wakefulness and circadian pressures are greater.^31^ Notably, none of the abovementioned reviews examined the potential role of naps or biphasic sleep as strategies to mitigate the negative consequences associated with disrupted sleep.
Limited evidence exists regarding whether shift workers benefit more from monophasic or biphasic sleep, and whether naps or a second sleep period can mitigate the consequences of shorter total sleep duration. Understanding how sleep strategies differ is important, as sleep structure can influence important outcomes, including physical and mental health, cognitive performance, alertness during working hours and subjective experiences.
A search for reviews in MEDLINE, Embase, PsycINFO, Web of Science and PROSPERO was conducted, but no published or planned systematic or scoping reviews on biphasic sleep among shift workers were identified.
Against this backdrop, we will conduct a scoping review to identify and summarise existing literature examining biphasic sleep compared with monophasic sleep among shift working populations. The review will also map the health, performance, alertness and subjective outcomes that have been examined in relation to biphasic sleep. In addition, it will identify evidence gaps and areas suitable for future systematic reviews. Overall, the objective of this scoping review is to describe the scope, extent and characteristics of the literature on the effects of biphasic versus monophasic sleep between shifts in shift workers.
This scoping review will be conducted in accordance with the Johanna Briggs Institute guidelines,^32^ and reported in line with the preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews (PRISMA-ScR). The protocol has been pre-registered in Open Science Framework (10.17605/OSF.IO/WY7KJ). The searches are planned to be conducted on 1 April 2026, after the protocol paper is finalised and published. Title and abstract screening will start immediately after the searches are run. Full-text screening will follow, and data extraction/charting is planned to start immediately after screening. The review and manuscript preparation are expected to be completed by August 2026.
In this review, biphasic sleep will be defined as an arrangement that consists of portioning the sleep time into two separate segments named “phases” or “bouts”.^22^ This may include (1) Two separate sleep segments and (2) The combination of a longer sleep period and a brief or longer nap. “Between work shifts” is defined as off-duty time between consecutive work periods. Studies will be eligible if they report or analyse more than one sleep period among shift workers between shifts. We will exclude studies exclusively focusing on naps taken during work hours. We will exclude studies focusing on naps taken during work hours.
The scoping review will include published articles according to the inclusion and exclusion criteria described below (Table 1). Although this scoping review focuses on biphasic sleep, studies on polyphasic sleep will not be excluded, as they may contribute relevant conceptual insights.
The systematic literature search strategy was developed by a research librarian (ILJ) and will be conducted in five electronic MEDLINE (Ovid), Embase (Ovid), PsycINFO (Ovid), Web of Science and CENTRAL. The search strategies for the databases were designed to identify studies examining the relationship between shift work, split sleep and long sleep. Each strategy was developed using a combination of controlled vocabulary (Medical Subject Headings terms in MEDLINE and CENTRAL, Emtree in Embase and APA Thesaurus terms in PsycINFO) along with relevant free-text keywords. Search terms will include concepts related to sleep duration (eg, “biphasic”, “split sleep”, “long sleep” and “naps”) and shift work (eg, “night shift”, “rotating shifts” and “irregular work schedules”). Boolean and proximity operators (eg, adj3, allowing up to two words between terms in any order) will be applied to refine the search and optimise sensitivity and specificity. The proposed search strategy has been peer reviewed by an independent librarian using PRESS (Peer Review of Electronic Search Strategies).^33^ All feedback from PRESS has been evaluated for relevance and incorporated into the final search strategy (see online supplemental methods).
Grey literature sources will not be systematically searched, as preliminary scoping indicates that research on biphasic and monophasic sleep in shift workers is largely published in peer-reviewed journals. However, reference lists of included studies will be screened to capture any unpublished or non-indexed material. Reference lists in the included articles will be assessed, as well as assessing papers identified with forward citation tracking using Google Scholar and Web of Science.
Following the search, all identified citations will be loaded into Covidence (https://www.covidence.org/), and automatically checked for duplicates. Each title and abstract will be independently screened by two reviewers to assess their compliance with the inclusion criteria. Calculation of interrater reliability (eg, Kappa) will be conducted.
Two independent reviewers will assess the full texts of the selected citations against the inclusion criteria. For articles excluded at this stage, the reasons for exclusion will be documented and reported in the scoping review. Any disagreements that arise between the reviewers at each stage of the selection process will be resolved through discussion, or by consulting a third reviewer.
The number of the resulting papers of the search and the study inclusion process will be presented in full in the final scoping review and presented in a PRISMA-ScR flow diagram.^34^
One researcher will extract data from each manuscript. A second researcher will review the extracted data and verify accuracy. If consensus cannot be reached, a third researcher will make the final decision for the study in question.
Data extraction will be performed using a standardised Excel spreadsheet including key study characteristics (Box 1, online supplemental file 1) and findings relevant to the scoping review question, including sleep or nap duration, the interval between sleep periods and the associated outcomes across the three domains of health, performance and alertness and subjective sleep outcomes.
Although quality assessments are not typically required in scoping reviews, the research team will consider the study designs to determine whether a quality assessment is warranted once the extraction of the included studies has been completed.
The results will first be summarised according to Box 1.
For the secondary research questions, data will be synthesised separately for the three outcome domains (health, performance and alertness, subjectively reported outcomes). Key outcomes and measurement approaches within each domain will be charted in more detail. Examples of outcomes in each category (1) Health outcomes (eg, cardiometabolic measures, pain and cancer), (2) Performance and alertness outcomes (eg, cognitive performance, reaction time, errors and safety incidents) and (3) Subjectively reported outcomes (eg, fatigue, sleep quality and sleepiness).
Results will be presented in summary tables or evidence maps to illustrate where comparative evidence exists and to highlight understudied or missing outcome areas. A narrative synthesis will describe how the findings relate to the review questions. No pooled effect estimates will be undertaken; however, graphical displays (eg, forest plots or similar visualisations) may be used where studies provide data suitable for visual representation.
This scoping review will synthesise evidence from studies published in peer-reviewed journals. As the review will not involve the collection of primary data or the inclusion of human participants, ethical approval is not required. The review will use data from publicly available sources only.
The findings will be disseminated through publication in a peer-reviewed journal and presentation at relevant scientific conferences. The results are expected to guide future systematic reviews and further research on sleep strategies among shift workers.