PONE-D-21-23813Sleep of shift workers in different shift-work systems assessed with actigraphyPLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This paper has focus on the association of different shift systems with sleep length and the structure of sleep both during work and free days, with a long follow-up for an experimental study. It investigated the association of five shift rosters on sleep using wrist actigraphs over 28 days. The paper adds to the current knowledge due to having indeed the scope on the whole shift roster. Up to now most earlier papers focus on shift-dependent associations, but often forget the significance of free days in the rosters for recovery, sleep and the also to the related overall circadian disruption influencing the health effects of shift work. The paper is also valuable due to having several well-established objective outcomes: sleep timing, duration, overall sleep debt, the quality of sleep (LIDS) and social jetlag – the latest giving indications on the circadian disruption that is probably most relevant for the long-term effects of shift work on health. Indeed, the paper has several original and interesting results, as described in the abstract and the first chapter of the discussion.

The sample is cross-sectional but large enough to study the five rosters – that are used generally also in other countries than Germany, increasing the value of the paper. Especially the results of the permanent night work and those of the quickly and slowly rotating shift rotas are interesting. The rosters are well described in the appendix.

The paper included many results, but they are comprehensive and instead of publishing each outcome in a different journal, bringing them all to one paper (if the paper limits allow this) supports the overall interpretation of the message.

Minor issues

- the title is a bit boring compared to the contents – could reflect more the added value of the paper

- abstract: methods: normally past tense is used “we investigated…” etc. Some sentences could also benefit from language revision to clarify the meanings

- did you select the most relevant results to the conclusions here (why focus on 12-hour shifts only)– compare to the conclusions of the main text that gives, I think, a better view of the key results

- introduction includes relevant literature

- material and methods: lines 171-172: do the definitions of day sleep and night sleep include all options? For example, how a sleep period starting at 03 am and ending at 11 am is scored?

- results: line 248 “experienced” hints to subjective data – did it come from a survey” I would say that workers with .. had the shortest shift work experience

- lines 265-267 explanation for the results (“cannot compensate”) should be in the discussion, not here – an interesting topic to discuss

- line 343: how did it differ? Please report in a way that we could read in which shift schedule the sleep quality was good, where it was bad. “Differed” is not too informative yet.

Reviewer #2: Main comments to authors:

The authors conclude in the abstract that “this study confirms that 12h-shifts are not associated with chronic sleep loss compared to 8h-shifts, when observing long time frames of four weeks”. Then in the main text conclusion “This study confirms that partial sleep deprivation but not chronic sleep loss is a common consequence of shift work”. I do not see where this rather strong conclusion is drawn from. The sleep durations on work days are <7 hours on average in all shift rotation conditions. Both schedules have chronic sleep loss - from the abstract conclusion is the point that both shift schedules are just as bad as each other? There is evidence from numerous laboratory studies that sleep restriction builds over time, and is not sufficiently “repaid” by 1-2 long recovery sleeps, with performance deficits showing a cumulative effect of chronic sleep loss. How, based on the data presented in this manuscript, is there evidence of no chronic sleep loss associated with shift work? This seems to go beyond what the data presented can determine.

“Circadian misalignment was quantified by social jetlag”. Social jetlag is not necessarily a measure of circadian misalignment, as you have no objective marker rhythms measured (e.g., melatonin). While social jetlag is sometimes used as a proxy, it is important to acknowledge that while it may indicate possible misalignment, it is not a direct measure of the clock, rather a sleep-based marker. Sleep can be misaligned with endogenous circadian rhythms, with wide inter-individual variation, particularly in shift workers. There are multiple reasons why shift workers sleep at different times, that are not all attributable to circadian disruption. I do not see how social jetlag can be an accurate measure of circadian disruption in this context. Rather it is a marker of how disrupted sleep timing is compared to free days.

During the sleep analysis, were the sleep on- and offsets derived from the device software compared with sleep diaries for any major discrepancies? This is a commonly used process to eliminate any obvious errors that can occur due to non-wear or individuals being still during wake times. Similarly, how were naps measured? Were naps derived using actigraphy only, or alongside sleep diaries? Shorter bouts of inactivity (e.g., watching a movie) can easily be misinterpreted as a nap when relying solely on actigraphy. Given the high rates of naps in this dataset, and the presence of both wrist actigraphy and sleep diaries, I would like more detail on how these were cross-checked.

Discussion line 365: The observation that permanent night shift workers did not adapt to the schedule in between work days is consistent with other studies examining circadian adaptation to permanent night shift schedules measured via objective phase markers, and also to behavioural/sleep observations similar to this study. I suggest including comparison or reference to this broader literature.

Discussion line 362: Chronotype is a term that is frequently misattributed, muddying the scientific literature of circadian timing, diurnal preference, and sleep timing. Chronotype does not refer to biological measurements of endogenous circadian timing such as melatonin or body temperature - it is a false equivalency to say that these measures are the same as sleep timing measures such as actigraphy or self-report questionnaires. The studies mentioned in this paragraph of the discussion are chronotype studies reporting sleep-derived metrics, not circadian phase measured via melatonin. The authors should either include studies that have examined changes in circadian timing in shift workers (e.g., Deacon & Arendt, 1996; Gibbs et al., 2007; Hansen et al., 2010; Stone et al 2018) and clarify terminology making the distinction clear, or remove reference to biological measurements in this paragraph.

Minor suggestions:

A minor request: could the authors consider reporting sleep durations in hours and minutes rather than minutes? In some places it is in hh:mm and others in minutes. I believe hh:mm is easier to interpret, though it is your choice.

Table 3 Overall duration [h] - should this be [min]?

“Earlier attempts to elucidate this relationship concentrated on … naïve sleep quality measures such as the percentage of time in bed spent actually sleeping” Why is this a naïve sleep quality measure? Naïve suggests there's a lack of experience, wisdom, or judgement in using sleep efficiency calculations as sleep quality (which is widely done in the sleep field). I'm curious about this statement? It could be interpreted as inflammatory, which I do not believe is the author's intention. Perhaps a different word might be better? Maybe the word "simplistic" might be a less contentious word choice?

Does the LIDS measure give any insight into when participants are sleeping between night shifts? For example, are individuals sleeping immediately after a shift, or remaining awake and sleeping before the next shift, are the different phenotypes? This is not critical to examine or include, but if these data are readily available it would be a valuable addition, as this is often assumed but not necessarily well described in the literature.

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Reviewer #1: No

Reviewer #2: No

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Social jetlag and sleep debts are altered in different rosters of night shift work

PONE-D-21-23813R1

Dear Dr. Casjens,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: (No Response)

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: (No Response)

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: (No Response)

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

Reviewer #2: (No Response)

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have addressed the referee comments well.

Reviewer #2: (No Response)

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Reviewer #1: Yes: Mikko Härmä

Reviewer #2: No