Abstract

Background

Shift work is associated with insufficient sleep, which can compromise worker alertness with ultimate effects on occupational health and safety. Adapting shift work schedules may reduce adverse occupational outcomes.

Objectives

To assess the effects of shift schedule adaptation on sleep quality, sleep duration, and sleepiness among shift workers.

Search methods

We searched CENTRAL, PubMed, Embase, and eight other databases on 13 December 2020, and again on 20 April 2022, applying no language restrictions.

Selection criteria

We included randomised controlled trials (RCTs) and non‐RCTs, including controlled before‐after (CBA) trials, interrupted time series, and cross‐over trials. Eligible trials evaluated any of the following shift schedule components.

• Permanency of shifts

• Regularity of shift changes

• Direction of shift rotation

• Speed of rotation

• Shift duration

• Timing of start of shifts

• Distribution of shift schedule

• Time off between shifts

• Split shifts

• Protected sleep

• Worker participation

We included studies that assessed sleep quality off‐shift, sleep duration off‐shift, or sleepiness during shifts.

Data collection and analysis

Two review authors independently screened the titles and abstracts of the records recovered by the search, read through the full‐text articles of potentially eligible studies, and extracted data. We assessed the risk of bias of included studies using the Cochrane risk of bias tool, with specific additional domains for non‐randomised and cluster‐randomised studies. For all stages, we resolved any disagreements by consulting a third review author. We presented the results by study design and combined clinically homogeneous studies in meta‐analyses using random‐effects models. We assessed the certainty of the evidence with GRADE.

Main results

We included 11 studies with a total of 2125 participants. One study was conducted in a laboratory setting and was not considered for drawing conclusions on intervention effects. The included studies investigated different and often multiple changes to shift schedule, and were heterogeneous with respect to outcome measurement.

Forward versus backward rotation

Three CBA trials (561 participants) investigated the effects of forward rotation versus backward rotation. Only one CBA trial provided sufficient data for the quantitative analysis; it provided very low‐certainty evidence that forward rotation compared with backward rotation did not affect sleep quality measured with the Basic Nordic Sleep Questionnaire (BNSQ; mean difference (MD) −0.20 points, 95% confidence interval (CI) −2.28 to 1.89; 62 participants) or sleep duration off‐shift (MD −0.21 hours, 95% CI −3.29 to 2.88; 62 participants). However, there was also very low‐certainty evidence that forward rotation reduced sleepiness during shifts measured with the BNSQ (MD −1.24 points, 95% CI −2.24 to −0.24; 62 participants).

Faster versus slower rotation

Two CBA trials and one non‐randomised cross‐over trial (341 participants) evaluated faster versus slower shift rotation. We were able to meta‐analyse data from two studies. There was low‐certainty evidence of no difference in sleep quality off‐shift (standardised mean difference (SMD) −0.01, 95% CI −0.26 to 0.23) and very low‐certainty evidence that faster shift rotation reduced sleep duration off‐shift (SMD −0.26, 95% CI −0.51 to −0.01; 2 studies, 282 participants). The SMD for sleep duration translated to an MD of 0.38 hours' less sleep per day (95% CI −0.74 to −0.01). One study provided very low‐certainty evidence that faster rotations decreased sleepiness during shifts measured with the BNSQ (MD −1.24 points, 95% CI −2.24 to −0.24; 62 participants).

Limited shift duration (16 hours) versus unlimited shift duration

Two RCTs (760 participants) evaluated 80‐hour workweeks with maximum daily shift duration of 16 hours versus workweeks without any daily shift duration limits. There was low‐certainty evidence that the 16‐hour limit increased sleep duration off‐shift (SMD 0.50, 95% CI 0.21 to 0.78; which translated to an MD of 0.73 hours' more sleep per day, 95% CI 0.30 to 1.13; 2 RCTs, 760 participants) and moderate‐certainty evidence that the 16‐hour limit reduced sleepiness during shifts, measured with the Karolinska Sleepiness Scale (SMD −0.29, 95% CI −0.44 to −0.14; which translated to an MD of 0.37 fewer points, 95% CI −0.55 to −0.17; 2 RCTs, 716 participants).

Shorter versus longer shifts

One RCT, one CBA trial, and one non‐randomised cross‐over trial (692 participants) evaluated shorter shift duration (eight to 10 hours) versus longer shift duration (two to three hours longer). There was very low‐certainty evidence of no difference in sleep quality (SMD −0.23, 95% CI −0.61 to 0.15; which translated to an MD of 0.13 points lower on a scale of 1 to 5; 2 studies, 111 participants) or sleep duration off‐shift (SMD 0.18, 95% CI −0.17 to 0.54; which translated to an MD of 0.26 hours' less sleep per day; 2 studies, 121 participants). The RCT and the non‐randomised cross‐over study found that shorter shifts reduced sleepiness during shifts, while the CBA study found no effect on sleepiness.

More compressed versus more spread out shift schedules

One RCT and one CBA trial (346 participants) evaluated more compressed versus more spread out shift schedules. The CBA trial provided very low‐certainty evidence of no difference between the groups in sleep quality off‐shift (MD 0.31 points, 95% CI −0.53 to 1.15) and sleep duration off‐shift (MD 0.52 hours, 95% CI −0.52 to 1.56).

Authors' conclusions

Forward and faster rotation may reduce sleepiness during shifts, and may make no difference to sleep quality, but the evidence is very uncertain. Very low‐certainty evidence indicated that sleep duration off‐shift decreases with faster rotation. Low‐certainty evidence indicated that on‐duty workweeks with shift duration limited to 16 hours increases sleep duration, with moderate‐certainty evidence for minimal reductions in sleepiness. Changes in shift duration and compression of workweeks had no effect on sleep or sleepiness, but the evidence was of very low‐certainty. No evidence is available for other shift schedule changes. There is a need for more high‐quality studies (preferably RCTs) for all shift schedule interventions to draw conclusions on the effects of shift schedule adaptations on sleep and sleepiness in shift workers.

Author(s)

Gerben Hulsegge, Pieter Coenen, Gregg M Gascon, Manisha Pahwa, Birgit Greiner, Ciarán Bohane, Imelda S Wong, Juha Liira, Rachel Riera, Daniela V Pachito

Abstract

Plain language summary

Changing shift worker's schedules to improve sleep quality and duration and reduce sleepiness

Key messages

• There is limited evidence that changes in shift schedules improve sleep quality, increase sleep duration, or reduce sleepiness.

• More studies are needed to draw stronger conclusions about shift schedule changes on sleep and sleepiness.

What can be done to improve shift workers' sleep?

Shift work often leads to insufficient sleep that can compromise worker alertness, with ultimate effects on health and work safety. Changing shift work schedules is one method that may reduce the unwanted effects of shift work.

What did we want to find out?

We wanted to find out which shift schedule adaptations improve sleep on rest days and reduce sleepiness at work.

What did we do?

We searched for studies that evaluated the following features of shift schedules.

• Whether shift schedules changed (rotated) or stayed the same

• Whether shift changes were regular or irregular

• Direction of shift rotation (morning to afternoon to night or night to afternoon to morning)

• Speed of rotation

• Shift duration

• Timing of start of shifts

• Distribution of shift schedule (fewer shifts with more hours or more shifts with fewer hours)

• Time off between shifts

• Split (interrupted) shifts

• Whether workers had on‐call shifts

• Whether workers were involved in organising the shift schedule

What did we find?

We included 11 studies, with 2125 participants. One study was conducted in a laboratory; we disregarded the results of this study when drawing conclusions. Most studies investigated a change in one feature of the shift schedule, while some investigated changes in two features. Four studies investigated the effect of changes in direction of shift rotation, three studies speed of rotation, five studies changes in shift duration, and one study changes in the distribution of days off.

Forward rotation compared to backward rotation may have no effect on sleep duration or sleep quality on rest days, but may reduce sleepiness at work. However, all of these results are very uncertain.

Faster shift rotation compared to slower shift rotation may have no effect on sleep quality on rest days. Faster rotation may reduce sleep duration on rest days, but may also reduce sleepiness at work; however, the evidence for both results is very uncertain.

Two studies investigated 80‐hour workweeks among doctors. They found that a schedule with shifts of no more than 16 hours, compared with a schedule with unlimited shift duration (including shifts of 24 to 28 hours), may increase sleep duration on rest days and probably results in a slight reduction in sleepiness at work.

Shorter shift duration (eight or 10 hours) compared to longer shift duration (two to three hours longer) may have no effect on sleep quality or sleep duration on rest days, but the results are very uncertain. The effects of shift duration on sleepiness differed across studies.

Changes in the distribution shift schedules (e.g. two days versus four days off in a row) may have no effect on sleep quality or sleep duration on rest days, but the results are very uncertain.

We found no studies investigating other changes in shift schedules.

Overall, there is a need for more high‐quality studies to draw firm conclusions on the effects of shift schedule changes on sleep and sleepiness. Currently, we cannot draw useful conclusions from the available evidence.

Main limitations of the evidence

Too few of the included studies allocated workers to the schedule change at random. In addition, many studies included few workers and lacked reliable measurements of sleep and sleepiness.

How up‐to‐date is this review?

The evidence is up‐to‐date to 13 December 2020.

Author(s)

Gerben Hulsegge, Pieter Coenen, Gregg M Gascon, Manisha Pahwa, Birgit Greiner, Ciarán Bohane, Imelda S Wong, Juha Liira, Rachel Riera, Daniela V Pachito

Reviewer's Conclusions

Authors' conclusions 

Implications for practice 

The available evidence indicates that some changes to shift systems may have a small effect on sleepiness and sleep, but evidence for effects on sleep quality is absent or uncertain. The literature provides very low‐certainty evidence that forward rotation compared with backward rotation, and faster rotation compared with slower rotation, results in a clinically relevant reduction in sleepiness during shifts. Although evidence from intervention studies is still limited, no harmful effects were reported in interventions associated with rapid forward rotation of night shifts. Due to lack of clear evidence, it is particularly important for organisations that change their shift schedule to involve employees and to evaluate the effects on employees.

Moderate‐certainty evidence indicates that setting shift limits at 16 hours during 80‐hour workweeks reduces sleepiness in resident physicians and interns in medical units, but this effect was small and not clinically relevant. For these shift schedule adaptations, there was also low‐certainty evidence of a clinically relevant increase in sleep after night shifts. Based upon all available evidence on sleep and sleepiness, organisations should be extremely careful with long workweeks and shift duration exceeding 16 hours.

We found very low‐certainty evidence that changes in shift duration or compression of workweeks have no effect on sleep and sleepiness. For the other shift schedule changes we found no evidence at all. As such, we cannot provide additional shift schedule recommendations.

When implementing or changing a shift schedule, it is important to consider the effects of shift schedules on other outcomes such as fatigue, mental health, and cardiometabolic parameters, as well as work productivity and feasibility.

Implications for research 

Most evidence in the literature was of low or very low certainty due to the scarcity of randomised controlled trials (RCTs) and other methodological limitations of the studies, including small sample sizes and subjective measurements of sleep and sleepiness. This implies that the true effect of shift schedule interventions could be substantially different from our estimates. High‐quality cluster‐RCTs conducted with objective and validated measurements of the outcomes and reported in line with CONSORT Cluster are needed to establish how shift schedules can be adapted to promote sleep and reduce sleepiness (Campbell 2012). These trials should be carried out systematically across work sectors (e.g. health, transportation) and geographic regions, documenting worker chronotype, age, and autonomy over working times to address potential interactions.

The studies included in this review used a wide range of instruments to measure sleep and sleepiness, and assessed these outcomes at different times across the control and intervention period. To better synthesise future research and make evidence more useful, researchers should use standard measurement instruments and protocols. We consider that shift work research would benefit from the development of a core outcome set.

There was a great variability regarding shift across studies. The lack of standardisation of working hours in the intervention and comparator arms was anticipated, considering real‐life variability of work schedules across economic sectors and geographic regions, but it hampered a broader assessment of the impact of shift duration on the outcomes of interest. Future research should aim to employ standardised shift durations that could provide more robust and meaningful evidence.

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