Abstract

Background

Shift work is often associated with sleepiness and sleep disorders. Person‐directed, non‐pharmacological interventions may positively influence the impact of shift work on sleep, thereby improving workers’ well‐being, safety, and health.

Objectives

To assess the effects of person‐directed, non‐pharmacological interventions for reducing sleepiness at work and improving the length and quality of sleep between shifts for shift workers.

Search methods

We searched CENTRAL, MEDLINE Ovid, Embase, Web of Knowledge, ProQuest, PsycINFO, OpenGrey, and OSH‐UPDATE from inception to August 2015. We also screened reference lists and conference proceedings and searched the World Health Organization (WHO) Trial register. We contacted experts to obtain unpublished data.

Selection criteria

Randomised controlled trials (RCTs) (including cross‐over designs) that investigated the effect of any person‐directed, non‐pharmacological intervention on sleepiness on‐shift or sleep length and sleep quality off‐shift in shift workers who also work nights.

Data collection and analysis

At least two authors screened titles and abstracts for relevant studies, extracted data, and assessed risk of bias. We contacted authors to obtain missing information. We conducted meta‐analyses when pooling of studies was possible.

Main results

We included 17 relevant trials (with 556 review‐relevant participants) which we categorised into three types of interventions: (1) various exposures to bright light (n = 10); (2) various opportunities for napping (n = 4); and (3) other interventions, such as physical exercise or sleep education (n = 3). In most instances, the studies were too heterogeneous to pool. Most of the comparisons yielded low to very low quality evidence. Only one comparison provided moderate quality evidence. Overall, the included studies’ results were inconclusive. We present the results regarding sleepiness below.

Bright light

Combining two comparable studies (with 184 participants altogether) that investigated the effect of bright light during the night on sleepiness during a shift, revealed a mean reduction 0.83 score points of sleepiness (measured via the Stanford Sleepiness Scale (SSS) (95% confidence interval (CI) ‐1.3 to ‐0.36, very low quality evidence). Another trial did not find a significant difference in overall sleepiness on another sleepiness scale (16 participants, low quality evidence).

Bright light during the night plus sunglasses at dawn did not significantly influence sleepiness compared to normal light (1 study, 17 participants, assessment via reaction time, very low quality evidence).

Bright light during the day shift did not significantly reduce sleepiness during the day compared to normal light (1 trial, 61 participants, subjective assessment, low quality evidence) or compared to normal light plus placebo capsule (1 trial, 12 participants, assessment via reaction time, very low quality evidence).

Napping during the night shift

A meta‐analysis on a single nap opportunity and the effect on the mean reaction time as a surrogate for sleepiness, resulted in a 11.87 ms reduction (95% CI 31.94 to ‐8.2, very low quality evidence). Two other studies also reported statistically non‐significant decreases in reaction time (1 study seven participants; 1 study 49 participants, very low quality evidence).

A two‐nap opportunity resulted in a statistically non‐significant increase of sleepiness (subjective assessment) in one study (mean difference (MD) 2.32, 95% CI ‐24.74 to 29.38, 1 study, 15 participants, low quality evidence).

Other interventions

Physical exercise and sleep education interventions showed promise, but sufficient data to draw conclusions are lacking.

Authors' conclusions

Given the methodological diversity of the included studies, in terms of interventions, settings, and assessment tools, their limited reporting and the very low to low quality of the evidence they present, it is not possible to determine whether shift workers' sleepiness can be reduced or if their sleep length or quality can be improved with these interventions.

We need better and adequately powered RCTs of the effect of bright light, and naps, either on their own or together and other non‐pharmacological interventions that also consider shift workers’ chronobiology on the investigated sleep parameters.

Author(s)

Tracy E Slanger, J. Valérie Gross, Andreas Pinger, Peter Morfeld, Miriam Bellinger, Anna‐Lena Duhme, Rosalinde Amancay Reichardt Ortega, Giovanni Costa, Tim R Driscoll, Russell G Foster, Lin Fritschi, Mikael Sallinen, Juha Liira, Thomas C Erren

Abstract

Plain language summary

Non‐drug interventions for sleepiness and sleep problems for shift workers who work nights

Summary text

People who work shifts, especially night shifts, often describe being sleepy at work or having sleep problems after work. This can be bad for their well‐being, safety, and health. On the basis of a systematic literature search, we evaluated whether person‐directed, non‐drug interventions can make shift workers less sleepy during their shift, and help them sleep longer and better after their shift is over.

Studies found

We found 17 randomised controlled trials (with 556 participants) to include in this review. We rated the quality of evidence provided by most of the included studies to be between low and very low. The studies could be divided into three different types of interventions: (1) exposure to bright light; (2) a napping opportunity during the night shift; or (3) others, like physical activity or sleep education.

Key results

Bright light

Almost all of the bright light studies we looked at had some problem with the way they were designed. This problem made it difficult to know if any differences in sleepiness and sleep between those receiving bright light and those not receiving bright light were truly because of the bright light intervention. The studies were also too different in the types of bright light they used and types of light that the control groups received to compare them to one another.

Napping

The studies in the napping group did not report enough information for us to be certain whether napping helps shift workers feel more awake. The studies were very short, with each study lasting only a single night.

Others

This group of studies, which included, for example, physical exercise and sleep education, also reported too little information for us to say whether these interventions can make shift workers less sleepy on‐shift or help them sleep longer and better after their shift.

Conclusion

We conclude that there is too much uncertainty to determine whether any person‐directed, non‐drug interventions can really affect shift workers with sleepiness and sleep problems. We need studies that are better designed, report their designs and results more clearly, include more participants and last for a longer time before we can be certain. Studies also need to find out if their participants are 'morning‐types' or 'evening‐types', to be sure that the right type of shift worker gets the right type of intervention.

How up‐to‐date is this review?

We searched for studies that had been published up to August 2015.

Author(s)

Tracy E Slanger, J. Valérie Gross, Andreas Pinger, Peter Morfeld, Miriam Bellinger, Anna‐Lena Duhme, Rosalinde Amancay Reichardt Ortega, Giovanni Costa, Tim R Driscoll, Russell G Foster, Lin Fritschi, Mikael Sallinen, Juha Liira, Thomas C Erren

Reviewer's Conclusions

Authors' conclusions 

Implications for practice 

Based on the current evidence base it is not possible to determine whether person‐directed, non‐pharmacological interventions including bright light, naps, physical exercise, or sleep education have any influence on outcomes including sleepiness, sleep length, and quality. All results from the pooled analyses, as well as results from the single trials should be interpreted with caution as we graded the quality of the evidence provided by most of the included studies as low to very low.

Implications for research 

Overall, there is a noticeable lack of interpretable evidence and study evidence of links between the interventions and outcomes investigated in this review. Our extensive literature searches and analyses culminate in the following guidelines for future studies in this field.

• Most studies appeared considerably underpowered to adequately identify or exclude practically and clinically important effects. Power and sample size calculations should be calculated before a study is conducted and systematically reported. The actual number of participants to make the study adequately powered will depend on the study specifics.

• Wherever possible, blinding should be applied.

• Future research must consider chronobiological aspects, such as the chronotype, to take note of the individual biological night and day and consider this information as a possible effect modifier. The tools chosen to assess chronotype should assess chronobiological propensity accurately. Unfortunately, to date there has been no consensus or standardisation regarding how chronotype should be most appropriately assessed in practice.

Questionnaires which can be used to assess chronobiological information include the Morningness‐Eveningness Questionnaire (MEQ) (Horne 1976), cited 1843 times as of 28 April 28 2016; the Munich Chronotype Questionnaire (MCTQ) (Roenneberg 2003), cited 429 times as of 28 April 28 2016; and the recently proposed MCTQshift (Juda 2013). Moreover, in place of – or to complement – questionnaires such as the MEQ or MCTQ, laboratory measurements such as the dim light melatonin onset (DLMO) tool could be employed as it is considered the most reliable measure of central circadian timing in humans (Kantermann 2015).

One example may illustrate challenges regarding the issue of how to consider chronotype in practice. When investigating possible relationships between shift work involving circadian disruption and cancer (IARC 2010), the assessment of chronobiological propensity has been based on answers to as little as one single question. In the relevant Hansen 2012 study, the authors referred to the Roenneberg 2007 study where the authors wrote in 2007, “It is remarkable that an introduction combined with a single question of self‐assessing one’s chronotype gives almost the same results as a questionnaire consisting of 19 items.” Importantly, the 'introduction + single question' reads: “Self‐assessment: After you have answered the preceding questions, you should have a feeling to which chronotype (time‐of‐day‐type) you belong to. …. Please tick only one possibility” (information added: out of seven categories) (MCTQ; Roenneberg 2003); p. 82).

To date, the extent to which the answer to the 'single question' is influenced by the answers to the preceding 19 questions is not clear. How well a single question without such preceding questions into chronobiological information can capture chronotype appears therefore open.

• Reports of studies should have comprehensive descriptions of the studies' methods (e.g. randomisation), data, and analyses. Furthermore, study location and the time period when a study was conducted should be reported.

• A general approach to make future research more informative could be to convene a panel of knowledgeable scientists from the different fields concerned (International Agency for Research on Cancer (IARC) example in Stevens 2011). Candidates for such a panel would include scientists from occupational medicine, chronobiology, and sleep medicine who could identify – at least a convincing minimum of – uniform study requirements. Such a panel could also attempt to resolve methodological controversies, e.g. which questionnaire(s) should be used and when it (they) should be used, or whether to use the DLMO tool in addition to, or instead of, other measures.

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