Night shift work, genetic risk, and the risk of depression: A prospective cohort study

BACKGROUND

Genetic factors and night shift work both contribute to the risk of depression, but whether the association of night shift work with depression varies by genetic predisposition remains unclear.

OBJECTIVES

To assess whether night shift work is associated with a higher risk of depression regardless of genetic predisposition.

METHODS

We used data from the UK biobank of 247,828 adults aged 38-71 free of depression at baseline from March 13, 2006, to October 1, 2010. Genetic predisposition to depression was assessed using polygenic risk scores (PRS) weighted sums of genetic variant indicator variables and classified as low (lowest tertile), intermediate (tertile 2), and high (highest tertile). Night shift work exposures were collected using a touchscreen questionnaire and were divided into four categories.

RESULTS

After a median follow-up of 12.7 years, 7315 participants developed depression. Compared with day workers, HRs (95 % CIs) of depression were 1.28 (1.19-1.38) for shift work, but never or rarely night shifts, 1.32 (1.20-1.45) for irregular night shifts, and 1.20 (1.07-1.34) for permanent night shifts. Considering lifetime employment and compared with never shift workers, >8 nights/month (HR: 1.40; 95 % CI: 1.19-1.66) and <10 years (HR: 1.30; 95 % CI: 1.09-1.54) of night shift work were associated with a higher risk of depression. In joint effect analyses, compared to participants with low genetic predisposition and day workers, the HRs (95 % CIs) of depression were 1.49 (1.32-1.69) in those with high genetic predisposition and shift work, but never or rarely night shifts, and 1.36 (1.20-1.55) for those with high genetic predisposition and irregular/permanent night shifts. In addition, there was neither multiplicative nor additive interaction between genetic predisposition and night shift work on the risk of depression.

CONCLUSIONS

Night shift work was associated with an increased risk of depression regardless of genetic risk.

Working hours and health - key research topics in the past and future

OBJECTIVE

This paper discusses the past and present highlights of working hours and health research and identifies key research needs for the future.

METHOD

We analyzed over 220 original articles and reviews on working hours and health in the Scandinavian Journal of Work, Environment & Health published during the last 50 years. Key publications from other journals were also included.

RESULTS

The majority of identified articles focussed on the effects of shift and night work, with fewer studying long and reduced working hours and work time control. We observed a transition from small-scale experimental and intensive field studies to large-scale epidemiological studies utilizing precise exposure assessment, reflecting the recent emergence of register-based datasets and the development of analytic methods and alternative study designs for randomized controlled designs. The cumulative findings provide convincing evidence that shift work and long working hours, which are often associated with night work and insufficient recovery, increase the risk of poor sleep and fatigue, sickness absence, occupational injuries, and several chronic health conditions such as cardiovascular diseases and cancer. The observed risks are strongly modified by individual and work-related factors.

CONCLUSIONS

Although the observed health risks of shift work and long working hours are mostly low or moderate, the widespread prevalence of exposure and the hazardousness of the many associated potential outcomes makes such working time arrangements major occupational health risks. Further research is needed to identify exposure-response associations, especially in relation to the chronic health effects, and to elucidate underlying pathways and effective personalized intervention strategies.

A 90- followed by a 30-min nap reduces fatigue whereas a 30- followed by a 90-min nap maintains cognitive performance in night work: A randomized crossover-pilot study

OBJECTIVE

To investigate the effects of combinations of brief naps (a 90- followed by a 30-min nap vs. a 30- followed by a 90-min nap) on sleep inertia, reducing sleepiness and fatigue, and maintaining performance during night hours.

METHODS

This randomized, comparative, repeated-measure, cross-over study investigated subjective and cognitive performance in 12 healthy females, evaluated in three experimental nap conditions: 1) from 22:30 to 00:00 and 02:30 to 03:00 (Pre90-NAP group), 2) from 23:30 to 00:00 and 02:30 to 04:00 (Pre30-NAP) group, and 3) no naps (NO-NAP group). Participants' body temperature, psychomotor vigilance task (PVT) and Uchida-Kraepelin test (UKT) scores, and subjective feelings of drowsiness and fatigue were evaluated. Sleep state was determined by an actigraphy monitoring device worn by participants.

RESULTS

Regardless of timing, both 90-min naps were associated with sleep inertia, and both 30-min naps with minimal sleep inertia. Reaction times were shorter and fewer errors were committed at 2 h post-nap in the Pre30-NAP and Pre90-NAP groups compared with those at the same time in the NO-NAP group. Adding a 90-min nap to a 30-min nap reduced subjective fatigue and shortened reaction times, and adding a 30-min nap to a 90-min nap was effective in maintaining performance, suggesting a synergistic effect.

CONCLUSIONS

Taking two naps during a night work can mitigate sleepiness and fatigue, and maintain performance. A 90- followed by a 30-min nap reduced fatigue and reaction time, and a 30- followed by a 90-min nap maintained cognitive performance in the early morning.

A Wake-Up Call to Address Nurse Fatigue

Research exploring differences in fatigue and sleep quality between day- and night-shift nurses highlights the urgent need for action to mitigate nurse fatigue. Nurses need to prioritize their sleep, and nurse leaders must take proactive measures such as providing education for all doing shiftwork, ensuring completion of job requirements during the shift, and creating a culture where nurses take their scheduled breaks.

Strategies that nurses working irregular night shifts use to improve sleep quality: A qualitative study among good and poor sleepers

AIMS

To assess the sleep strategies that nurses working irregular night shifts use to improve their sleep quality, and to compare the strategies of good and poor sleepers to determine whether the differences between the two groups could provide insights into possible effective strategies.

DESIGN

A qualitative descriptive study.

METHODS

The study was conducted from September 2019 to January 2020. Thirty-four nurses working irregular night shifts participated; 17 were classified as good sleepers and 17 as poor sleepers based on the Sleep-Wake Experience List, a validated self-report instrument that measures one's sleep quality. Interviews were conducted using open questions to explore strategies around the night-shift set. The interviews were analysed using thematic analysis.

FINDINGS

Both groups described similar and different strategies that help them work and sleep well during and after night shifts. However, good sleepers mentioned a greater number of strategies and seemed to have thought about them more than poor sleepers. The most common strategies were having a clear structure, being organized-especially regarding sleeping time-maintaining a daily routine and adjusting their sleep environment.

CONCLUSION

Healthcare institutions should consider offering education and training programs aimed at empowering nurses who work irregular night shifts. These programs should provide nurses with various sleep strategies to enhance their sleep quality and overall well-being.

IMPLICATIONS FOR THE PROFESSION

Nurses working irregular night shifts can possibly enhance their sleep quality by making personalized plans, for example, including a clear day structure, or an optimized sleep environment.

IMPACT

The study focused on how nurses working night shifts could possibly enhance their sleep quality. The findings highlight the importance of providing nurses with diverse sleep strategies to improve sleep quality, helping them to identify what works best for them and consistently apply these strategies.

REPORTING METHOD

The Consolidated Criteria for Reporting Qualitative Research guidelines were followed.

PATIENT OR PUBLIC CONTRIBUTION

Nurses working irregular night shifts at Maastricht University Medical Center in Maastricht, the Netherlands, who agreed to participate in the study, engaged in a discussion to assess the relevance of sleep quality to their work. They were also encouraged to share their perspectives during the interviews.

Relationship between long working hours and smoking behaviors: Evidence from population-based cohort studies in Korea

OBJECTIVES

Long working hours and overwork are growing public health concerns in the Western-Pacific region. We explored the relationship between working hours and smoking behaviors of Korean workers.

METHODS

This study included 284 782 observations (50 508 workers) from four nationwide cohort studies in Korea. Using generalized estimating equations, we estimated the associations of working hours with current smoking status, smoking initiation, and smoking cessation within each cohort. Cohort-specific estimates were combined through random-effect meta-analysis. Effect sizes were presented as odds ratios (OR) and 95 confidence intervals (CI).

RESULTS

The overall smoking prevalence was 26.8% within the cohorts. The adjusted OR (95% CI) of the association between working hours and current smoking were 1.01 (0.94-1.08) for <35 hours/week, 1.04 (1.01-1.09) for 41-48 hours/week, 1.06 (1.01-1.10) for 49-54 hours/week, and 1.07 (1.04-1.10) for ≥55 hours/week compared with 35-40 hours/week. The adjusted OR (95% CI) of the association between working hours and smoking cessation in the follow-up were 0.93 (0.85-1.02) for <35 hours/week, 0.89 (0.83-0.96) for 41-48 hours/week, 0.87 (0.81-0.95) for 48-54 hours/week, and 0.91 (0.85-0.98) for ≥55 hours/week compared with 35-40 hours/week. No clear associations were observed between working hours and smoking initiation.

CONCLUSION

Long working hours are associated with high current smoking risk and reduced likelihood of smoking cessation among Korean workers. Policy interventions are required to promote smoking cessation and reduce excess overwork for individuals experiencing long working hours.

Changes in work schedule affect headache frequency among Norwegian nurses: a 3-year-follow-up study

OBJECTIVES

To explore whether changes in work schedule, number of night shifts and number of quick returns were related to changes in headache frequencies.

METHODS

A longitudinal study with questionnaire data from 2014 (baseline) and 2017 (follow-up) on work schedule (day only, shift work without nights and shift work with nights), number of night shifts, number of quick returns (less than 11 hours in-between shifts) and validated headache diagnoses among 1104 Norwegian nurses. Associations were explored by adjusted multivariate regression analyses.

RESULTS

The median age at baseline was 37 years (IQR 31-43) and 90.5% were women. In the adjusted logistic regression analysis of changed work schedule between baseline and follow-up, changing from night work was associated with increased odds for reversion from headache >1 days/month to no headache at all last year (OR 2.77 (1.29; 5.95)). Changes towards less night shifts (>10) or quick returns (>10) during the last year were associated with increased odds of reversion of headache to no headache (OR 2.23 (1.20; 4.17) and OR 1.90 (1.04; 3.49)). Only decrease in number of night shifts (>10) during the last year reduced risk of onset of any new headache between baseline and follow-up (OR of 0.39 (0.18; 0.84)).

CONCLUSION

Changing from night work and reducing the number of night shifts and quick returns were associated with less headache in this 3-year-follow-up of Norwegian nurses. This adds to the growing body of evidence that night work may have direct negative health consequences.

[Advance in occupational health risks and management of shift work]

The occupational health issues of shift workers has received increasing attention in the field of occupational health, and discussed in this article through literature review on the health risks and management of shift work both domestically and internationally. Based on this, a series of impacts of shift work on the physiological and psychological health of workers, as well as their family and social life, are revealed. Combined with relatively mature regulations and policies in foreign countries, it is proposed that China should fully learn from the relevant experience of health management in shift work abroad, Strengthen research and explore effective management intervention measures to provide ideas for accelerating the development of scientifically feasible regulations and policies related to occupational health in shift work in China.

Association of rotating night shift work with tooth loss and severe periodontitis among permanent employees in Japan: a cross-sectional study

Background

The modern 24/7 society demands night shift work, which is a possible risk factor for chronic diseases. This study aimed to examine the associations of rotating night shift work duration with tooth loss and severe periodontitis.

Methods

This cross-sectional study used data from a self-administered questionnaire survey conducted among 3,044 permanent employees aged 20-64 years through a Japanese web research company in 2023. The duration of rotating night shift work was assessed using a question from the Nurses' Health Study. Tooth loss was assessed based on self-reported remaining natural teeth count. Severe periodontitis was assessed using a validated screening questionnaire comprising four questions related to gum disease, loose tooth, bone loss, and bleeding gums. We employed linear regression models for tooth loss and Poisson regression models for severe periodontitis, adjusting for demographic, health and work-related variables and socioeconomic status.

Results

Among participants included, 10.9% worked in rotating night shifts for 1-5 years, while 11.0% worked in such shifts for ≥6 years. In fully adjusted models, rotating night shift work duration of 1-5 years was associated with tooth loss (beta -0.74, 95% confidence interval (CI) [-1.55 to 0.08]) and severe periodontitis (prevalence ratio 1.80, 95% CI [1.33-2.43]); however, the association with tooth loss was not statistically significant.

Conclusions

This study supports that employees who work short-term rotating night shifts may experience poor oral conditions. Further research is needed to determine whether long-term rotating night shift work is associated with deteriorated oral health.

Cohort Studies Versus Case-Control Studies on Night-Shift Work and Cancer Risk: The Importance of Exposure Assessment

It is a general assumption that the prospective cohort study design is the gold standard approach and is superior to the case-control study design in epidemiology. However, there may be exceptions if the exposure is complex and requires collection of detailed information on many different aspects. Night-shift work, which impairs circadian rhythms, is an example of such a complex occupational exposure and may increase the risks of breast, prostate, and colorectal cancer. So far, for logistical reasons, investigators in cohort studies have assessed shift work rather crudely, lacking information on full occupational history and relevant shift-work metrics, and have presented mostly null findings. On the other hand, most cancer case-control studies have assessed the lifetime occupational histories of participants, including collection of detailed night-shift work metrics (e.g., type, duration, intensity), and tend to show positive associations. In this commentary, we debate why cohort studies with weak exposure assessment and other limitations might not necessarily be the preferred or less biased approach in assessing the carcinogenicity of night-shift work. Furthermore, we propose that risk-of-bias assessment and comparison of associations between studies with low versus high risks of bias be considered in future synthesis of the evidence.

Sleep and Risk of Pancreatic Cancer in the UK Biobank

BACKGROUND

Light at night, which may cause circadian disruption, is a potential pancreatic cancer risk factor. However, evidence from related exposures such as poor sleep health and shift work remains inconclusive and sparsely investigated.

METHODS

We evaluated associations between self-reported typical sleep duration, chronotype, shift work, insomnia symptoms, snoring, and daytime sleeping and pancreatic ductal adenocarcinomas (PDAC) incidence among 475,286 UK Biobank participants. We used Cox proportional hazards models to estimate HRs and 95% confidence intervals (CI) adjusting for age, sex, body mass index, smoking status, duration, and frequency, alcohol intake, diabetes status, race, and employment/shift work.

RESULTS

Over 14 years of follow-up, 1,079 adults were diagnosed with PDAC. There were no associations observed between sleep characteristics, including sleep duration [<7 vs. 7-<9 hours; HR, 1.03; 95% CI, 0.90-1.19; ≥9 hours; HR, 1.00 (0.81-1.24), evening chronotype ("definitely" an evening person vs. "definitely" a morning person; HR, 0.99 (0.77-1.29)], shift work, insomnia symptoms, snoring, or daytime sleep and PDAC risk.

CONCLUSIONS

Self-reported typical sleep characteristics and shift work were not associated with PDAC risk.

IMPACT

Considering the role of light at night and shift work in circadian disruption and cancer risk, it is plausible that poor sleep health among a general population may be related to cancer risk through similar sleep and circadian disrupting processes. This work may suggest that typical sleep characteristics and shift work are not associated with PDAC, although additional work is needed to confirm these findings.

Validity of self-reported night shift work among women with and without breast cancer

OBJECTIVES

This study aimed to estimate the validity of self-reported information on ever-night shift work among women with and without breast cancer and illustrate the consequences for breast cancer risk estimates.

METHODS

During 2015-2016, 225 women diagnosed with breast cancer and 1800 matched controls without breast cancer employed within the Danish hospital regions during 2007-2016 participated in a questionnaire-based survey. Their reported night shift work status was linked with objective payroll register day-by-day working hour data from the Danish Working Hour Database and the Danish Cancer Registry. For the breast cancer patients and their matched controls, we estimated sensitivity and specificity for ever-working night shifts using the payroll data as the gold standard. We also used quantitative bias analysis to estimate the impact on relative risk estimates for a hypothetical population.

RESULTS

For breast cancer patients, we observed a sensitivity of ever-night shifts of 86.2% and a specificity of never-night shifts of 82.6%. For controls, the sensitivity was 80.6% and the specificity 83.7%. Odds ratio for breast cancer in a hypothetical population decreased from 1.12 [95% confidence interval (CI) 1.03-1.21] to 1.05 (95% CI 0.95-1.16) when corrected by the sensitivity and specificity estimates.

CONCLUSION

This study shows that female breast cancer patients had slightly better recall of previous night shift work than controls. Additionally, both breast cancer patients and controls recalled previous never-night shift work with low specificity. The net effect of this misclassification is a small over-estimation of the relative breast cancer risk due to night shift work.

Night shift work and cardiovascular diseases among employees in Germany: five-year follow-up of the Gutenberg Health Study

OBJECTIVE

This study aimed to determine if there is an increased risk of incident cardiovascular diseases (CVD) resulting from cumulative night shift work in the German population-based Gutenberg Health Study (GHS).

METHODS

We examined working participants of the GHS at baseline and after five years. Cumulative night shift work in the 10 years before baseline was assessed and categorized as low (1-220 nights ≙ up to 1 year), middle (221-660 nights ≙ 1-3 years), and high (>660 nights ≙ more than 3 years) night shift exposure. Hazard ratios (HR) were estimated for incident "quality-assured CVD events" using Cox proportional hazard models.

RESULTS

At baseline, 1092 of 8167 working participants performed night shift work. During the follow-up, 202 incident cardiovascular events occurred. The crude incidence rates for CVD per 1000 person-years were 6.88 [95% confidence interval (CI) 4.80-9.55] for night shift workers and 5.19 (95% CI 4.44-6.04) for day workers. Cumulative incidence curves showed a higher cumulative incidence in workers exposed to night shift work compared to day workers after five years. The adjusted HR for incident CVD events were 1.26 (95% CI 0.68-2.33), 1.37 (95% CI 0.74-2.53) and 1.19 (95% CI 0.67-2.12) for employees in the low, middle and high night shift categories compared to employees without night shift work, respectively.

CONCLUSIONS

The observed tendencies indicate that night shift work might be negatively associated with cardiovascular health. We expect the continued follow-up will clarify the long-term impact of night shift work.

Working hours and cardiovascular disease

Working hours, including the number and the arrangement thereof – such as shift work, night work, and quick returns – are classic topics in research on work environment and health. The struggle for working time reduction and the eight-hour work day is also one of the oldest fights of the labor movement, dating back to the 19th century (1). International Workers’ Day, celebrated annually on 1 May, has its origin in the Haymarket Affair, a rally in support of a strike for the eight-hour work day at the Haymarket Square in Chicago, USA, on 4 May 1886. At the rally, a riot broke out and a bomb exploded, killing several workers and police officers. In the aftermath, the State of Illinois prosecuted labor movement activists. Although the person who throw the bomb was never identified and the circumstances of the attack remained unclear, four labor movement activists, including August Spies, the editor of the German-American newspaper Arbeiter-Zeitung, were executed by hanging on 11 November 1887. A fifth activist died by suicide in prison (2).

When the International Labour Organization (ILO) was established as an agency of the newly created League of Nations (the predecessor of today’s United Nations) after World War I in 1919, one of its main aims was the regulation and reduction of working time (1). The demand for the 8-hour work day and 48-hour work week was even included in the peace treaty of Versailles (Part XIII, Section II, Article 427) that was signed on 28 June 1919 following World War I (3, 4).

Although working hours have been greatly reduced in many high-income countries since the 19th century, particularly in Europe, the discussion about working hours remains topical, as can be seen by the recent debate about a 4-day working week (5, 6). In South-East and East Asian countries, such as Japan, South Korea, and Taiwan, where working hours >48 hours per week are still widely prevalent, health concerns of such long working hours are an important topic of discussion (7, 8). Notably, the Japanese language has coined two terms: karōshi for death due to overwork (usually of cardiovascular causes) and karōjisatsu for death by suicide due to overwork (9). At the Scandinavian Journal of Work, Environment & Health, we regularly receive papers from researchers in Asia examining the health effects of long working hours (10–12). This issue includes a paper from a German research group on the association between night shift work and risk of cardiovascular disease (13). I use this opportunity to reflect briefly in this editorial on research on working hours and cardiovascular health. In the May issue (number 4) of the Journal, as part of our 50-year anniversary special publication series (14, 15), there will be a much more detailed account on what we have learned so far on working hours and health.

Long working hours and cardiovascular disease In 2015, Kivimäki et al (16) published a seminal paper on long working hours and cardiovascular disease for the Individual Participant Data Meta-Analysis of Working Population (IPD-Work) Consortium that showed an association of long working hours with an increased risk of both ischemic heart disease and stroke (16). The association was stronger for stroke than ischemic heart disease (pooled relative risks 1.33 versus 1.13). Furthermore, for stroke, but not ischemic heart disease, the analyses suggested an exposure–response pattern. Thus, the longer the working hours, the greater the risk of stroke.

From 2017 to 2021, the World Health Organization (WHO) and ILO conducted a project on the WHO/ILO Joint Estimates of the Work-Related Burden of Disease and Injury (17, 18) that included systematic reviews on the association of long working hours and risk of ischemic heart disease (19) and stroke (20). Results were similar to those reported by the IPD-Work Consortium in 2015. Long working hours, defined as ≥55 hours per week, were associated with a small increased risk of ischemic heart disease (pooled risk ratio 1.17) (19) and a larger increased risk of stroke (pooled risk ratio 1.35) (20). Based on these risk estimates and estimates on the country-specific prevalence of long working hours, the WHO and ILO estimated that, in 2016, globally 745 194 deaths were attributable to long working hours, with the largest burden in South-East Asia (17, 18, 21). A summary of the WHO/ILO joint estimates project has been published as a discussion paper in our Journal (22), together with an editorial (23).

Obviously, the estimate of approximately 750 000 annual deaths due to long working hours is based on several assumptions, including that the epidemiological studies` estimates indicate a causal association between long working hours and cardiovascular outcomes and that data on the worldwide prevalence of long working hours are valid. Kivimäki and colleagues (24) expressed concerns about the interpretation that there is sufficient evidence for harmfulness of long working hours with regard to ischemic heart disease. Among other things, the authors were concerned about residual confounding (eg, by health-related behaviors, although it is debated whether they are mainly confounders, for which one should control, or mediators, for which one should not control (25)). They also presented analyses of data that suggested that socioeconomic position might be an important effect modifier and that the harmful effect of long working hours on risk of ischemic heart disease may be limited to workers of low socioeconomic position. As socioeconomic position is linked to the type of work the workers are doing, the possible effect modification by socioeconomic position could also mean that other, unmeasured working conditions may modify the association between long working hours and health. In other words, in addition to the length of the working hours, what happens during these working hours might also be important. In Denmark, Hannerz and colleagues (26, 27) attempted to replicate the analyses on long working hours and ischemic heart disease and stroke using large-scale register data. With regard to ischemic heart disease, they did not find an increased risk with long working hours [rate ratio (RR) 1.07, 95% confidence interval (CI) 0.94–1.21 for >48 versus 32–40 hours] (26). When stratified by socioeconomic position, long working hours were not associated with an increased risk of ischemic heart disease among workers of high, medium and unknown socioeconomic position, but there was an increased risk among workers of low socioeconomic position that worked long hours (RR 1.27, 95% CI 1.05–1.53). Although the interaction `long working hours × socioeconomic position` was not statistically significant, this increased risk among workers of low socioeconomic position is in agreement with the analyses by Kivimäki et al (24). With regard to stroke, Hannerz et al (27) did not find an increased risk for all types of stroke combined among those with long working hours, however, they reported an association between long working hours and increased risk of hemorrhagic stroke. This result was recently replicated in an analysis of the French CONSTANCES study (28) where exposure to long working hours during the past ten years was, in the adjusted model, associated with an increased risk of hemorrhagic stroke but not ischemic stroke.

One can summarize that during the past ten years, several large-scale studies and meta-analyses on long working hours and cardiovascular outcomes have been published. Whereas the WHO has concluded that there is sufficient evidence for harmfulness for the association between long working hours and ischemic heart disease and stroke (19–21), other studies point to possible effect modification by socioeconomic position (24, 26) with regard to ischemic heart disease and the need to distinguish between ischemic and hemorrhagic stroke (27, 28).

Shift work, night shift work and cardiovascular disease In 2018, Torquati et al (29) published a systematic review and meta-analysis that showed an increased risk of cardiovascular disease among shift workers. For those working shifts for five years, each additional five-year period of shift work was associated with a 7% increased risk of cardiovascular disease.

Night shift work has been of particular interest for cancer research (30) but might also be relevant with regard to cardiovascular diseases. In their recent review and meta-analysis, Su et al (31) reported that night shift work was associated with an increased risk of cardiovascular mortality (pooled estimate 1.15, 95% CI 1.03–1.29). However, only four studies were included in this review. In 2022, a Swedish research group published two papers on night shift work from a large sample of healthcare workers in Stockholm, one on cerebrovascular disease and the other on ischemic heart disease. Bigert et al (32) reported that frequent night shifts and frequent consecutive night shifts were associated with an increased risk of cerebrovascular disease, including stroke. Kader et al (33) reported that permanent night shifts and frequent night shifts were associated with an increased risk of ischemic heart disease. In Denmark, Vestergaard et al (34)examined the association between night shift work and ischemic heart disease in a large-cohort of healthcare workers with day-to-day payroll information. The results were less clear than those of Kader et al (33): male, but not female, healthcare workers with night work had an increased risk of ischemic heart disease compared to day-time workers. The paper by Jankowiak et al (13) in the current issue of the Journal examined night shift work and risk of cardiovascular disease in a population-based cohort in the city of Mainz and Mainz-Bingen in Germany (13). The hazard ratios for low, middle, and high night shift work were 1.19, 1.32, and 1.14, respectively, compared to no night shift work, in the most-adjusted model. An important strength of the study is the comprehensive clinical examination of the participants, both at baseline and follow-up. An important limitation is the very low number of cases in the exposure groups during the five-year follow-up. Unsurprisingly, the CI of all estimates were wide and included unity and, thus, were far away from being statistically significant. The uncertainty of the estimates do not allow firm conclusions on the results. However, the estimates from this study can be included in meta-analyses, which then may provide us with more insight on the role of night shift work on risk of cardiovascular disease.

Important challenges for future research on working time and cardiovascular disease will include better use of electronic working time registration systems that will allow a more precise measurement of exposure to long working hours and the frequency and type of shift work and night shift work (35, 36). It will also be important to conceptually clarify whether health behaviors that are hazardous to cardiovascular health – such as certain dietary patterns, lack of leisure time physical activity, or smoking – are confounders or mediators, or both, for the association between working time and cardiovascular disease. This clarification is key to correctly handling data on these health behaviors in the statistical models. Finally, examining the relations of the different working time arrangements with the contents of work conducted during these arrangements might be fruitful for a better understanding of the contribution of work to cardiovascular disease.

Conflict of interest statement Reiner Rugulies was involved in both the IPD-Work Consortium and the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury project. References 1. International Labour Organization (ILO). International Labour Standards on Working time [Website]. 2024. Available from: https://www.ilo.org/global/standards/subjects-covered-by-international-labour-standards/working-time/lang--en/index.htm. (Accessed: 26 Februar 2024). 2. Chicago Historical Society and the Trustees of Northwestern University. The dramas of Haymarket [Website]. 2000. Available from: https://www.chicagohistoryresources.org/dramas/. (Accessed: 26 February 2024). 3. Yale Law School. The Avalon Project: Documents in Law, History and Diplomay. The Versailles Treaty June 28, 1919: Part XIII [Website]. 2008. Available from: https://avalon.law.yale.edu/imt/partxiii.asp. (Accessed: 2 March 2024). 4. International Labour Office. Official Bulletin, Volume I, April 1919 - August 1920. 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Night shift work and cardiovascular diseases among employees in Germany: five-year follow-up of the Gutenberg Health Study. Scand J Work Environ Health. 2024;50(3):142–151. https://doi.org/10.5271/sjweh.4139 14. Rugulies R, Burdorf A. The achievements and challenges of occupational health research: Looking back and ahead. Scand J Work Environ Health. 2024;50(1):1-2. https://doi.org/10.5271/sjweh.4136 15. Burdorf A, Rugulies R. Fifty years of research in the Scandinavian Journal of Work, Environment & Health. Scand J Work Environ Health. 2024;50(1):3-10. https://doi.org/10.5271/sjweh.4135 16. Kivimäki M, Jokela M, Nyberg ST, Singh-Manoux A, Fransson EI, Alfredsson L, et al. Long working hours and risk of coronary heart disease and stroke: a systematic review and meta-analysis of published and unpublished data for 603,838 individuals. Lancet. 2015;386(10005):1739-1746. https://doi.org/10.1016/S0140-6736(15)60295-1 17. 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Descatha A, Sembajwe G, Pega F, Ujita Y, Baer M, Boccuni F, et al. The effect of exposure to long working hours on stroke: A systematic review and meta-analysis from the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury. Environ Int. 2020;142:105746. https://doi.org/10.1016/j.envint.2020.105746 21. Pega F, Náfrádi B, Momen NC, Ujita Y, Streicher KN, Prüss-Üstün AM, et al. Global, regional, and national burdens of ischemic heart disease and stroke attributable to exposure to long working hours for 194 countries, 2000-2016: A systematic analysis from the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury. Environ Int. 2021;154:106595. https://doi.org/10.1016/j.envint.2021.106595 22. Pega F, Hamzaoui H, Nafradi B, Momen NC. Global, regional and national burden of disease attributable to 19 selected occupational risk factors for 183 countries, 2000-2016: A systematic analysis from the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury. Scand J Work Environ Health. 2022;48(2):158-168. https://doi.org/10.5271/sjweh.4001  23. Coggon D. Estimating population burdens of occupational disease. Scand J Work Environ Health. 2022;48(2):83-85. https://doi.org/10.5271/sjweh.4007 24. Kivimäki M, Virtanen M, Nyberg ST, Batty GD. The WHO/ILO report on long working hours and ischaemic heart disease - Conclusions are not supported by the evidence. Environ Int. 2020;144:106048. https://doi.org/10.1016/j.envint.2020.106048 25. Li J, Rugulies R, Morgan RL, Woodruff T, Siegrist J, WHO/ILO Working Group of Individual Experts on Long Working Hours on Ischaemic Heart Disease. 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Torquati L, Mielke GI, Brown WJ, Kolbe-Alexander T. Shift work and the risk of cardiovascular disease. A systematic review and meta-analysis including dose-response relationship. Scand J Work Environ Health. 2018;44(3):229-238. https://doi.org/10.5271/sjweh.3700 30. IARC Working Group on the Identification of Carcinogenic Hazards to Humans. Night shift work. Lyon, France: IARC; 2020. Available from: https://publications.iarc.fr/_publications/media/download/6397/c965a667eda3a390d9797cbcde59765fef9dcb7a.pdf. (Accessed: 29 February 2024). 31. Su F, Huang D, Wang H, Yang Z. Associations of shift work and night work with risk of all-cause, cardiovascular and cancer mortality: a meta-analysis of cohort studies. Sleep Med. 2021;86:90-98. https://doi.org/10.1016/j.sleep.2021.08.017 32. Bigert C, Kader M, Andersson T, Selander J, Bodin T, Gustavsson P, et al. Night and shift work and incidence of cerebrovascular disease - a prospective cohort study of healthcare employees in Stockholm. 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Impact of 24 h shifts on urinary catecholamine in emergency physicians: a cross-over randomized trial

24-h shift (24 hS) exposed emergency physicians to a higher stress level than 14-h night shift (14 hS), with an impact spreading on several days. Catecholamines are supposed to be chronic stress biomarker. However, no study has used catecholamines to assess short-term residual stress or measured them over multiple shifts. A shift-randomized trial was conducted to study urinary catecholamines levels of 17 emergency physicians during a control day (clerical work on return from leave) and two working day (14 hS and 24 hS). The Wilcoxon matched-pairs test was utilized to compare the mean catecholamine levels. Additionally, a multivariable generalized estimating equations model was employed to further analyze the independent relationships between key factors such as shifts (compared to control day), perceived stress, and age with catecholamine levels. Dopamine levels were lower during 24 hS than 14 hS and the control day. Norepinephrine levels increased two-fold during both night shifts. Epinephrine levels were higher during the day period of both shifts than on the control day. Despite having a rest day, the dopamine levels did not return to their normal values by the end of the third day after the 24 hS. The generalized estimating equations model confirmed relationships of catecholamines with workload and fatigue. To conclude, urinary catecholamine biomarkers are a convenient and non-invasive strong measure of stress during night shifts, both acutely and over time. Dopamine levels are the strongest biomarker with a prolonged alteration of its circadian rhythm. Due to the relation between increased catecholamine levels and both adverse psychological effects and cardiovascular disease, we suggest that emergency physicians restrict their exposure to 24 hS to mitigate these risks.

[Relationship between thyroid function changes with work-/night-shifts and history of thyroid pathology among health personnel]

BACKGROUND

The study aim was to analyze the relationship between functional thyroid pathology and the exposure to work shifts / night shifts, and describe the most prevalent thyroid disorders based on the type of shift.

METHODOLOGY

Cross-sectional study performed in the emergency department of a hospital in Almeria (Spain). Relationships between thyroxine and thyrotropin levels (TSH) and work shifts, professional category and history of thyroid pathology were analyzed.

RESULTS

The study included 133 workers; 80.5% female, average age was 46.11 years (38 - 65), and 52% were part of the nursing staff; thyroid disorders were more frequent in female participants. Most participants (81.2%) had rotating shifts schedules and 11.3% night shifts (12.1% female and 7.7% male). Thyroid alterations were found in 27% of the participants (usually elevated TSH levels and normal thyroxine levels), particularly in those doing night shifts (61.1%). TSH alterations were more frequent in individuals doing night shifts than in rotating shifts (53.3 vs 13.0%; p<0.001). Individuals working night shifts had mean TSH values in the normal range, although significantly higher than the individuals in the rest of the shifts; thyroxine levels were found to be similar. No thyroid disorders were found in day shift participants. Night shift and a history of thyroid pathology were independent predictors of thyroid disorders.

CONCLUSIONS

Night shift schedules and history of thyroid disorders are more frequent in female, both related to the presence of thyroid disorders, indicating the need to include the evaluation of these disorders in health surveillance programs and analyze gender differences.

Move the night way: how can physical activity facilitate adaptation to shift work?

Shift work, involving night work, leads to impaired sleep, cognition, health and wellbeing, and an increased risk of occupational incidents. Current countermeasures include circadian adaptation to phase shift circadian biomarkers. However, evidence of real-world circadian adaptation is found primarily in occupations where light exposure is readily controlled. Despite this, non-photic adaptation to shift work remains under researched. Other markers of shift work adaptation exist (e.g., improvements in cognition and wellbeing outcomes) but are relatively unexplored. Timeframes for shift work adaptation involve changes which occur over a block of shifts, or over a shift working career. We propose an additional shift work adaptation timeframe exists which encompasses acute within shift changes in markers of adaptation. We also propose that physical activity might be an accessible and cost-effective countermeasure that could influence multiple markers of adaptation across three timeframes (Within Shift, Within Block, Within Work-span). Finally, practical considerations for shift workers, shift work industries and future research are identified.

The relationship between quick return shift schedules and burnout among nurses: A prospective repeated measures multi-source study

BACKGROUND

In today's world, essential health care services are expected round the clock, leading to distinct shift work requirements. A notable aspect is the "quick return," where the rest interval between nursing shifts is <11 h. Preliminary research suggests a potential association between quick return schedules, diminished sleep quality, and possible nurse burnout. Yet, the motivation of nurses could potentially moderate this relationship.

OBJECTIVE

To examine a moderated-mediation model, whereby sleep duration and nurse's motivation act together to mediate the link between quick return schedules and nurse's burnout.

DESIGN

A prospective repeated measures (4-5 nursing shifts per nurse) multi-source (self-report and objective measures) study.

SETTING

Internal and surgical departments across one large and one medium scale teaching hospitals in Israel.

PARTICIPANTS

Registered nurses who provide direct patient care (n = 79) across 369 shifts.

METHODS

Nurses completed a questionnaire containing personal information and information regarding their shifts during the study week. They wore an accelerometer (a wrist worn device that monitors and records an individual's activity level) during a work-week to objectively determine their sleep duration, completed a motivation questionnaire at the beginning of each shift, and completed a burnout questionnaire at the end of the week. Mixed-model regression analysis was used to test a moderated-mediation model following Hayes' recommendations, whereby the joint effect of sleep duration and motivation mediates the link between quick return schedules and burnout.

RESULTS

The moderated-mediation model was supported. Quick return schedules were negatively statistically significantly associated with sleep duration (b = -126.54, SE = 20.85, p < 0.001); so that more frequent quick return schedules were related to shorter sleep duration. However, no direct correlation was observed between sleep duration and burnout (p = 0.171). A statistically significant interaction was observed between sleep duration and motivation (b = 0.00, SE = 0.00, p < 0.001) concerning burnout. Thus, nurses with lower motivation were prone to experiencing higher levels of burnout with shorter sleep duration compared to nurses with higher motivation.

CONCLUSIONS

The mediating role of sleep duration, moderated by motivation, plays a role in the connection between quick return schedules and burnout. This indicates that nurses can sustain their work motivation even within the demands of quick return schedules, consequently mitigating burnout levels. To prioritize employees' well-being, organizations should adopt shift work structures that minimize quick return schedules and extend nurses' sleep duration. Consequently, managers must employ strategies to enhance nurses' motivation when addressing scenarios that necessitate quick return schedules.

Shift Work Adversely Affects Sleep

According to this study.

Relationships among meal time, break time and workplace characteristics of nurses who work day, evening and night shifts: a cross-sectional study

Objectives. This study aimed to examine the relationships among shift-working nurses' meal time, break time and workplace characteristics. Methods. The cross-sectional study analyzed 351 questionnaires from 117 nurses who worked three shifts, drawn from eight nursing units in two tertiary hospitals located in South Korea. Meal time and break time during work were investigated through a questionnaire that participants completed immediately after the end of each shift. Regression analysis was conducted to investigate the associations between nurses' work characteristics and meal time and break time. Results. Meal time and break time were less than 30 min on all shifts and significantly longer on the night shift than on the other shifts. As patients' average length of stay increased, meal time increased on day and night shifts, while break time decreased on evening shifts. Overall, a higher nursing staff-to-patient ratio was associated with shorter meal and break times. Conclusions. It was found that nurses were not able to take proper time for meals and breaks while working. A realistic and specific strategy should be prepared to address this issue, with appropriate consideration of the specific characteristics of nurse staffing, patients' conditions and shifts.

Factors affecting the psychomotor vigilance of nurses working night shift

BACKGROUND

Shifts and long working hours decrease the psychomotor vigilance of healthcare workers especially when working night shifts. Working night shifts adversely affects nurses' health and impacts patient safety.

AIM

The purpose of this study is to identify factors affecting the psychomotor vigilance of nurses working night shift.

METHODS

This descriptive cross-sectional study was carried out with 83 nurses who were working in a private hospital in Istanbul and voluntarily participated in this study between April 25 and May 30, 2022. Data were collected using "Descriptive Characteristics Form," "Psychomotor Vigilance Task," "Pittsburgh Sleep Quality Index," and "Epworth Sleepiness Scale." The "STROBE checklist" for cross-sectional studies was utilized in order to report the findings of the study.

RESULTS

When time-dependent variation of the nurses' psychomotor vigilance task performances on the night shift was examined, it was observed that the nurses' mean reaction time and number of lapses increased at the end of the night shift. Age, smoking, physical activity, daily water consumption, daytime sleepiness, and sleep quality were found as the factors affecting nurses' psychomotor vigilance.

CONCLUSION

The psychomotor vigilance task performances of nurses working night shift are affected by age and a variety of behavioral factors.

IMPLICATIONS FOR NURSING AND HEALTH POLICY

Suggestions for nursing policy include the implementation of workplace health promotion programs in order to increase the attention level of nurses in order to ensure employee and patient health and safety and create a healthy working environment.

The important factors nurses consider when choosing shift patterns: A cross-sectional study

AIM

To gain a deeper understanding of what is important to nurses when thinking about shift patterns and the organisation of working time.

DESIGN

A cross-sectional survey of nursing staff working across the UK and Ireland collected quantitative and qualitative responses.

METHODS

We recruited from two National Health Service Trusts and through an open call via trade union membership, online/print nursing profession magazines and social media. Worked versus preferred shift length/pattern, satisfaction and choice over shift patterns and nurses' views on aspects related to work and life (when working short, long, rotating shifts) were analysed with comparisons of proportions of agreement and crosstabulation. Qualitative responses on important factors related to shift preferences were analysed with inductive thematic analysis.

RESULTS

Eight hundred and seventy-three survey responses were collected. When nurses worked long shifts and rotating shifts, lower proportions reported being satisfied with their shifts and working their preferred shift length and pattern. Limited advantages were realised when comparing different shift types; however, respondents more frequently associated 'low travel costs' and 'better ability to do paid overtime' with long shifts and 'healthy diet/exercise' with short shifts; aspects related to rotating shifts often had the lowest proportions of agreement. In the qualitative analysis, three themes were developed: 'When I want to work', 'Impacts to my life outside work' and 'Improving my work environment'. Reasons for nurses' shift preferences were frequently related to nurses' priorities outside of work, highlighting the importance of organising schedules that support a good work-life balance.

RELEVANCE TO CLINICAL PRACTICE

General scheduling practices like adhering to existing shift work guidelines, using consistent and predictable shift patterns and facilitating flexibility over working time were identified by nurses as enablers for their preferences and priorities. These practices warrant meaningful consideration when establishing safe and efficient nurse rosters.

PATIENT OR PUBLIC CONTRIBUTION

This survey was developed and tested with a diverse group of stakeholders, including nursing staff, patients, union leads and ward managers.

REPORTING METHOD

The Strengthening the Reporting of Observational Studies (STROBE) checklist for cross-sectional studies was used to guide reporting.

How much advance notice do workers need? A review and theoretical framework for determining advance notice periods for unpredictable work

Regulatory guidance materials for fatigue management typically advise that employees be provided with days or weeks of advance notice of schedules/rosters. However, the scientific evidence underpinning this advice is unclear. A systematic search was performed on current peer reviewed literature addressing advance notice periods, which found three relevant studies. A subsequent search of grey literature to determine the quality of evidence for the recommendation for advance notice periods returned 37 relevant documents. This review found that fatigue management guidance materials frequently advocated advance notice for work shifts but did not provide empirical evidence to underpin the advice. Although it is logical to suggest that longer notice periods may result in increased opportunities for pre-work preparations, improved sleep, and reduced worker fatigue, the current guidance appears to be premised on this reasoning rather than empirical evidence. Paradoxically, it is possible that advance notice could be counterproductive, as too much may result in frequent alterations to the schedule, particularly where adjustments to start and end times of the work period are not uncommon (e.g., road transport, rail). To assist organisations in determining the appropriate amount of advance notice to provide, we propose a novel theoretical framework to conceptualise advance notice.

Considering the impact of shift working on health

Shift work is necessary for the provision of health services, especially in hospitals as it is the only way to provide continuous care to patients. Working at night is inconsistent with the body's biological clock and night shift working hugely disrupts the circadian and sleep wake cycles. In 2020, the World Health Organization classified night shift working as being a 'probable' class 2A carcinogen and a number of independent cohort studies of both night workers and shift workers have observed increased incidence of certain cancers. Altered sleep timing, food timing and light exposure typical for shift workers leads to an acute circadian disruption and misalignment of regulatory hormones. This straying from synchronisation has been shown to result in individuals being more vulnerable to a number of chronic health conditions. Night shift work disrupts the normal sleep-wake cycle, often leading to shortened sleep duration and excessive fatigue and the results of this are far reaching. This article will explore the full impact of shift working, questioning if current practices employed within the NHS should continue.

Awake at the wheel: how auto technology innovations present ongoing sleep challenges and new safety opportunities

Individuals and society are dependent on transportation. Individuals move about their world for work, school, healthcare, social activities, religious and athletic events, and so much more. Society requires the movement of goods, food, medicine, etc. for basic needs, commerce, cultural and political exchanges, and all of its dynamic, complex elements. To meet these critical daily demands, the transportation system operates globally and around the clock. Regardless of their role, a basic requirement for the individuals operating the transportation system is that they are awake and at optimal alertness. This applies to individuals driving their own cars, riding a bike or motorcycle, as well as pilots of commercial aircraft, train engineers, long-haul truck drivers, and air traffic controllers. Alert operators are a basic requirement for a safe and effective transportation system. Decades of scientific and operational research have demonstrated that the 24/7 scheduling demands on operators and passengers of our transportation system create sleep and circadian disruptions that reduce alertness and performance and cause serious safety problems. These challenges underly the longstanding interest in transportation safety by the sleep and circadian scientific community. An area currently offering perhaps the most significant opportunities and challenges in transportation safety involves vehicle technology innovations. This paper provides an overview of these latest innovations with a focus on sleep-relevant issues and opportunities. Drowsy driving is discussed, along with fatigue management in round-the-clock transportation operations. Examples of cases where technology innovations could improve or complicate sleep issues are discussed, and ongoing sleep challenges and new safety opportunities are considered.

Evaluation of sleep strategies between night shifts in actual shift workers

OBJECTIVES

The aim of this observational study was to examine sleep obtained between consecutive night shifts from shift workers in their natural environment. The goal was to identify the various sleep strategies and the timing, duration, regularity, and quality of sleep associated with the strategies.

METHODS

Participants (N = 33, 23 women, aged 40 ± 15years) reported their sleep information in daily diaries over 2weeks while working at least one series of consecutive night shifts. Sleep timing, duration, quality, and regularity were calculated for each sleep episode between consecutive night shifts.

RESULTS

Based on the reported sleep behavior, shift workers were categorized as either morning, delayed, split- or mixed sleepers. We found significant differences between the groups in timing of sleep, feeling refreshed, and regularity of sleep between consecutive night shifts, whereas duration and subjective soundness of sleep did not show significant differences.

CONCLUSIONS

In this sample, four sleep strategies were observed between consecutive night shifts in actual shift workers. These observations may help design future interventions to improve sleep that are individualized to the worker.

Determinants of fatigue in emergency department clinicians who wear personal protective equipment

OBJECTIVE

To determine the independent predictors for clinician fatigue and decline in cognitive function following a shift in the ED during early stages of the COVID-19 pandemic.

METHODS

This was a prospective, quasi-experimental study conducted in a metropolitan adult tertiary-referral hospital ED over 20 weeks in 2021. The participants were ED doctors and nurses working clinical shifts in an ED isolation area or high-risk zone (HRZ) with stringent personal protective equipment (PPE). The participants' objective and subjective fatigue was measured by the Samn-Perelli fatigue score and a psychomotor vigilance 'smart game' score, respectively. Postural signs/symptoms and urine specific gravity (SG) were measured as markers of dehydration.

RESULTS

Sixty-three participants provided data for 263 shifts. Median (interquartile range) age was 33 (28-38) years, 73% were female. Worsening fatigue score was associated with working afternoon shifts (afternoon vs day, adjusted odds ratio [aOR] 5.16 [95% confidence interval (CI) 1.32-20.02]) and in non-HRZ locations (HRZ vs non-HRZ, aOR 0.23 [95% CI 0.06-0.87]). Worsening cognitive function (game score) was associated with new onset postural symptoms (new vs no symptoms, aOR 4.14 [95% CI 1.34-12.51]) and afternoon shifts (afternoon vs day, aOR 3.13 [95% CI 1.16-8.44]). Working in the HRZ was not associated with declining cognitive function. Thirty-four (37%) of the 92 participants had an end of shift urine SG >1.030.

CONCLUSION

Working afternoon shifts was associated with fatigue. There was no association between HRZ allocation and fatigue, but our study was limited by a low COVID workload and fluctuating PPE requirements in the non-HRZs. Workplace interventions that target the prevention of fatigue in ED clinicians working afternoon shifts should be prioritised.

The associations between different types of infections and circadian preference and shift work

Disturbed sleep and circadian disruption are reported to increase the risk of infections. People with an evening circadian preference and night workers typically report insufficient sleep, and the aims of the present study were to investigate possible associations between various types of infections and circadian preference and shift work status. Data were collected from an online cross-sectional survey of 1023 participants recruited from the Norwegian practice-based research network in general practice - PraksisNett. The participants completed questions about circadian preference (morning type, intermediate type, evening type), work schedule (day work, shift work without nights, shift work with night shifts), and whether they had experienced infections during the last three months (common cold, throat infection, ear infection, sinusitis, pneumonia/bronchitis, COVID-19, influenza-like illness, skin infection, gastrointestinal infection, urinary infection, venereal disease, eye infection). Data were analyzed with chi-square tests and logistic regression analyses with adjustment for relevant confounders (gender, age, marital status, country of birth, children living at home, and educational level). Results showed that evening types more often reported venereal disease compared to morning types (OR = 4.01, confidence interval (CI) = 1.08-14.84). None of the other infections were significantly associated with circadian preference. Shift work including nights was associated with higher odds of influenza-like illness (OR = 1.97, CI = 1.10-3.55), but none of the other infections. In conclusion, neither circadian preference nor shift work seemed to be strongly associated with risk of infections, except for venereal disease (more common in evening types) and influenza-like illness (more common in night workers). Longitudinal studies are needed for causal inferences.

Public opinion of resident physician work hours in 2022

OBJECTIVE

The purpose of this study was to characterize public awareness and opinion regarding resident physician work hours in the United States.

METHODS

We conducted a nationally representative cross-sectional survey among adults in the United States. Demographic quota-based sampling was conducted by Qualtrics to match 2020 United States Census estimates of age, sex, race, and ethnicity. Descriptive statistics are presented. Hypothesis testing was conducted to identify characteristics associated with agreement with current resident physician work-hour policies.

RESULTS

4763 adults in the United States participated in the study. 97.1% of the public believes that resident physicians should not work 24-hour shifts and 95.6% believe the current 80 hours resident work week is too long. 66.4% of the participants reported that the maximum shift duration should be 12 consecutive hours or fewer, including 22.9% who recommended a maximum shift length of 8 hours. Similarly, 66.4% reported that maximum weekly work hours should be 59 or fewer, including 24.9% who recommended a maximum of 40 weekly work hours.

CONCLUSIONS

Nearly all US adults disagree with current work-hour policies for resident physicians. Public opinion supports limiting shifts to no more than 12 consecutive hours and weekly work to no more than 60 hours, which is in sharp contrast to current regulations that permit of 28 hours shifts and 80 hours of work per week.

Predicting neurobehavioral performance of resident physicians in a Randomized Order Safety Trial Evaluating Resident-Physician Schedules (ROSTERS)

OBJECTIVES

Mathematical models of human neurobehavioral performance that include the effects of acute and chronic sleep restriction can be key tools in assessment and comparison of work schedules, allowing quantitative predictions of performance when empirical assessment is impractical.

METHODS

Using such a model, we tested the hypothesis that resident physicians working an extended duration work roster, including 24-28 hours of continuous duty and up to 88 hours per week averaged over 4weeks, would have worse predicted performance than resident physicians working a rapidly cycling work roster intervention designed to reduce the duration of extended shifts. The performance metric used was attentional failures (ie, Psychomotor Vigilance Task lapses). Model input was 169 actual work and sleep schedules. Outcomes were predicted hours per week during work hours spent at moderate (equivalent to 16-20 hours of continuous wakefulness) or high (equivalent to ≥20 hours of continuous wakefulness) performance impairment.

RESULTS

The model predicted that resident physicians working an extended duration work roster would spend significantly more time at moderate impairment (p = .02, effect size=0.2) than those working a rapidly cycling work roster; this difference was most pronounced during the circadian night (p < .001). On both schedules, performance was predicted to decline from weeks 1 + 2 to weeks 3 + 4 (p < .001), but the rate of decline was significantly greater on extended duration work roster (p < .01). Predicted performance impairment was inversely related to prior sleep duration (p < .001).

CONCLUSIONS

These findings demonstrate the utility of a mathematical model to evaluate the predicted performance profile of schedules for resident physicians and others who experience chronic sleep restriction and circadian misalignment.

Circadian adaptation to night shift work is associated with higher REM sleep duration

OBJECTIVE

To investigate the influence of the degree of circadian adaptation to night work on sleep architecture following night shift.

METHODS

Thirty four night workers (11 females; 33.8 ± 10.1years) completed a simulated night shift following 2-7 typical night shifts. Participants completed a laboratory-based simulated night shift (21:00-07:00 hours), followed by a recovery sleep opportunity (∼09:00-17:00 hours), recorded using polysomnography. Urinary 6-sulphatoxymelatonin (aMT6s) rhythm acrophase was used as a marker of circadian phase. Sleep duration and architecture were compared between individuals with aMT6s acrophase before (unadapted group, n = 22) or after (partially adapted group, n = 12) bedtime.

RESULTS

Bedtime occurred on average 2.16 hours before aMT6s acrophase in the partially adapted group and 3.91 hours after acrophase in the unadapted group. The partially adapted group had more sleep during the week before the simulated night than the unadapted group (6.47 ± 1.02 vs. 5.26 ± 1.48 hours, p = .02). After the simulated night shift, both groups had similar total sleep time (partially adapted: 6.68 ± 0.80 hours, unadapted: 6.63 ± 0.88 hours, p > .05). The partially adapted group had longer total rapid eye movement sleep duration than the unadapted group (106.79 ± 32.05 minutes vs. 77.90 ± 28.86 minutes, p = .01). After 5-hours, rapid eye movement sleep accumulation was higher in the partially adapted compared to the unadapted group (p = .02). Sleep latency and other stages were not affected by circadian adaptation.

DISCUSSION

Partial circadian adaptation to night shift was associated with longer rapid eye movement sleep duration during daytime sleep, highlighting the influence of entrainment between the sleep-wake cycle and the circadian pacemaker in night workers. The findings have important implications for sleep and subsequent alertness associated with shift work.

Interindividual variability in coherence between self-reported alertness and performance in shift workers

OBJECTIVES

Evidence indicates that self-reported measures of alertness do not always reflect performance impairments. The present study aims to explore whether subjective and objective measures of vigilance vary in the same direction in individuals working nights.

METHODS

A total of 76 police officers participated to a month-long observational study. They worked either a 2 or 3-shift system during which they self-reported alertness and completed a psychomotor vigilance task several times a day.

RESULTS

A reduction in alertness and reaction speed was observed with time awake. At the group level, changes in alertness and reaction speed with time awake were positively correlated during night shifts only. In 63.6% of the officers, changes were coherent between both variables. The other officers reported that their alertness dropped (25.5%) or improved (10.9%) whereas their performance changed in the opposite direction.

CONCLUSION

Significant interindividual variability exists in self-appraisal vigilance impairment due to night shift work.

Effects of a simulated maritime shift schedule on vigilance, sleep, and sleepiness

Shift work is associated with circadian misalignment, which causes sleep loss, impairs performance, and increases the risk of accidents. Shorter, more frequently shifting watch schedules, widely used in industries such as maritime operation, defense, and mining, may mitigate these risks by reducing shift length and providing sleep opportunities for all workers across the biological night. However, the effects of frequently shifting work on sleep and performance still need to be clarified. The current study investigated the vigilance, sleepiness, and sleep patterns of fifteen participants who lived in a controlled and confined laboratory that mimicked a maritime environment for 14 d following a simulating frequent shift schedule. The results of psychomotor vigilance tasks (PVT) suggest that this shift schedule may lead to an accumulation of vigilance detrimental across watch days, with both reaction speed impairment and error growth. Furthermore, the circadian phase significantly affects PVT performance, with the afternoon shift section showing relatively better performance. Overall, more working hours per day resulted in poorer PVT performance. As the shift progressed, total sleep duration reduced slightly, and wake after sleep onset (WASO) increased. Sleep during the biological night was generally longer than sleep in the daytime. Less on-watch time was linked to longer overall sleep duration. Additionally, although the subjective sleepiness obtained by the Karolinska Sleepiness Scale (KSS) varied insignificantly across days, the KSS score was negatively correlated with PVT performance. This research can serve as a foundation for developing countermeasures to mitigate frequently shifting schedules' potentially detrimental effects and safety risks.

Circadian Adaptation of Melatonin and Cortisol in Police Officers Working Rotating Shifts

Misalignment of behavior and circadian rhythms due to night work can impair sleep and waking function. While both simulated and field-based studies suggest that circadian adaptation to a nocturnal schedule is slow, the rates of adaptation in real-world shift-work conditions are still largely unknown. The aim of this study was to evaluate the extent of adaptation of 24-h rhythms with 6-sulfatoxymelatonin (aMT6s) and cortisol in police officers working rotating shifts, with a special attention to night shifts. A total of 76 police officers (20 women; aged 32 ± 5.4 years, mean ± SD) from the province of Quebec, Canada, participated in a field study during their 28- or 35-day work cycle. Urine samples were collected for ~32 h before a series of day, evening, and night shifts to assess circadian phase. Before day, evening, and night shifts, 60%-89% of officers were adapted to a day schedule based on aMT6 rhythms, and 71%-78% were adapted based on cortisol rhythms. To further quantify the rate of circadian adaptation to night shifts, initial and final phases were determined in a subset of 37 officers with suitable rhythms for both hormones before and after 3-8 consecutive shifts (median = 7). Data were analyzed with circular and linear mixed-effects models. After night shifts, 30% and 24% of officers were adapted to a night-oriented schedule for aMT6s and cortisol, respectively. Significantly larger phase-delay shifts (aMT6s: -7.3 ± 0.9 h; cortisol: -6.3 ± 0.8 h) were observed in police officers who adapted to night shifts than in non-adapted officers (aMT6s: 0.8 ± 0.9 h; cortisol: 0.2 ± 1.1 h). Consistent with prior research, our results from both urinary aMT6s and cortisol midpoints indicate that a large proportion of police officers remained in a state of circadian misalignment following a series of night shifts in dim-light working environments.

Associations between long-term night shift work and incidence of chronic obstructive pulmonary disease: a prospective cohort study of 277,059 UK Biobank participants

BACKGROUND

Little is known about the effects of night shifts and their interactions with genetic factors on chronic obstructive pulmonary disease (COPD). In this study, we aim to investigate relationships between long-term night shift work exposure and COPD risk, and assess modification effects of genetic predisposition.

METHODS

A total of 277,059 subjects who were in paid employment or self-employed were included in the UK Biobank. Information on current and lifetime employment was obtained, and a weighted COPD-specific genetic risk score (GRS) was constructed. We used Cox proportional hazard models to investigate associations between night shift work and COPD risk, and their interaction with COPD-specific GRS.

RESULTS

The cohort study included 277,059 participants (133,063 men [48.03%]; mean [SD] age, 52.71 [7.08] years). During a median follow-up of 12.87 years, we documented 6558 incidents of COPD. From day work, irregular night shifts to regular night shifts, there was an increased trend in COPD incidence (P for trend < 0.001). Compared with day workers, the hazard ratio (HR) and 95% confidence interval (CI) of COPD was 1.28 (1.20, 1.37) for subjects with rarely/sometimes night shifts and 1.49 (1.35, 1.66) for those with permanent night shifts. Besides, the longer durations (especially in subjects with night shifts ≥ 10 years) and increasing monthly frequency of night shifts (in workers with > 8 nights/month) were associated with a higher COPD risk. Additionally, there was an additive interaction between night shifts and genetic susceptibility on the COPD risk. Subjects with permanent night shifts and high genetic risk had the highest risk of COPD (HR: 1.90 [95% CI: 1.63, 2.22]), with day workers with low genetic risk as a reference.

CONCLUSIONS

Long-term night shift exposure is associated with a higher risk of COPD. Our findings suggest that decreasing the frequency and duration of night shifts may offer a promising approach to mitigating respiratory disease incidence in night shift workers, particularly in light of individual susceptibility.

The association between proportion of night shifts and musculoskeletal pain and headaches in nurses: a cross-sectional study

BACKGROUND AND PURPOSE

Shift work is associated with musculoskeletal pain and headaches, but little is known about how the intensity of shift work exposure is related to musculoskeletal pain and headaches. This study aimed to investigate whether a higher proportion of night shifts is associated with a higher occurrence of musculoskeletal pain and headaches. Furthermore, to investigate whether sleep duration can mediate this potential association.

METHOD

The study included 684 nurses in rotating shift work who responded to a daily questionnaire about working hours, sleep, and pain for 28 consecutive days. The data were treated cross-sectionally.

RESULTS

A negative binomial regression analysis adjusted for age and BMI revealed that working a higher proportion of night shifts is not associated with a higher occurrence of musculoskeletal pain and headaches. On the contrary, those working ≥ 50% night shifts had a significantly lower occurrence of pain in the lower extremities than those who worked < 25% night shifts (IRR 0.69 95% CI 0.51, 0.94). There was no indication of a mediation effect with total sleep time (TST).

CONCLUSION

The results of this study indicate that working a higher proportion of night shifts is not associated with a higher occurrence of musculoskeletal pain and headaches.

Circadian epidemiology: Structuring circadian causes of disease and practical implications

That disruptions of the body's internal clockwork can lead to negative health consequences, including cancer, is a plausible hypothesis. Yet, despite strong mechanistic and animal support, the International Agency for Research on Cancer (IARC) experts considered epidemiological evidence as limited regarding the carcinogenicity of "shift-work involving circadian disruption" (2007) and "night shift work" (2019). We use directed acyclic graphs (DAGs) to outline a concept of circadian causes that discloses challenges when choosing appropriate exposure variables. On this basis, we propose to move beyond shift-work alone as a direct cause of disease. Instead, quantifying chronodisruption as individual doses can lead to interpretable circadian epidemiology. The hypothesis is that doses of chronodisruption cause disrupted circadian organisation by leading to desynchronization of circadian rhythms. Chronodisruption can be conceptualized as the split physiological nexus of internal and external times. Biological (or internal) night - an individual's intrinsically favoured sleep time window - could be the backbone of circadian epidemiology. In practice, individual doses that cause disrupted circadian organisation are derived from the intersection of time intervals of being awake and an individual's biological night. After numerous studies counted work shifts, chronobiology may now advance circadian epidemiology with more specific dose estimation - albeit with greater challenges in measurement (time-dependent individual data) and analysis (time-dependent confounding).

Effect of Mandatory and Voluntary Overtime Hours on Stress Among 9-1-1 Telecommunicators

BACKGROUND

9-1-1 telecommunicators are frequently exposed to indirect traumatic events that impact their mental and physical health and are often required to work overtime with rotating shifts. Previous studies reported various harmful effects of overtime on the health and well-being of workers, such as musculoskeletal injuries, burnout, low job satisfaction, fatigue, and intent to leave. However, there is limited research on the impact of overtime hours on 9-1-1 telecommunicators' stress symptoms, especially mandatory overtime hours. This study aimed to examine the relationship between overtime hours-mandatory and voluntary-and the level of stress symptoms among 9-1-1 telecommunicators.

METHODS

We used secondary data from the surveys of the "Multi-tasking to hyper-tasking: Investigating the impact of Next Generation 9-1-1" study for analysis. Linear mixed-effects regression was applied to examine the association of overtime hours with the stress level.

RESULTS

Of the 403 participants, 47.6% reported that they were required to work mandatory overtime, and the mean mandatory overtime was 7.51 (SD = 12.78) hours in the past month. 58.3% reported working voluntary overtime, and the mean voluntary overtime was 11.63 (SD = 17.48) hours. This study found that mandatory overtime hours were associated with an increase in self-reported stress symptoms (β = 0.30, p = .002), whereas no significant association was found between voluntary overtime and the level of stress symptoms (β = -0.01, p = .885).

CONCLUSION/APPLICATION TO PRACTICE

Study results highlight the importance of reducing mandatory overtime in call centers as one possible strategy for reducing stress levels among this critical workforce.

Relationship between working hours and sleep quality with consideration to effect modification by work style: a community-based cross-sectional study

BACKGROUND

Although longer working hours are associated with lower sleep quality, it is still necessary to work a certain number of hours to make a living. In this study, we investigated the relationship between working hours and sleep quality in a community setting. We then explored how to manage work style while maintaining the sleep quality of workers without markedly reducing working hours.

METHODS

4388 day-time workers in various occupations living in Ota ward in Tokyo were included in the analysis. The relationship between working hours and sleep quality measured by the Athens Insomnia Scale was examined by ANOVA and linear regression models. Effect modification by work style (work end time, shift in working start and end time, current work from home status, change in work place) on the relationship between working hours and sleep quality was investigated by multivariate linear regression models.

RESULTS

Longer working hours were significantly associated with lower sleep quality. The magnitude of the relationship between long working hours and low sleep quality was significantly larger when work end time was later (p for trend of interaction < 0.01) and when working start and end time were shifted later (vs no change, p for interaction = 0.03). The relationship was marginally greater when the proportion of work from home was increased (vs no change, p for interaction = 0.07).

CONCLUSIONS

A relationship between longer working hours and lower sleep quality was observed among workers. Leaving work earlier or optimizing the work environment at home may diminish the adverse effect of long working hours on sleep quality.

Maternal Circadian Disruption from Shift Work and the Impact on the Concentration of Melatonin in Breast Milk

Background and Objective: Melatonin in breast milk exhibits a 24-hour circadian rhythm, present in nighttime breast milk but nearly undetectable in daytime breast milk. Shift work can disrupt the circadian timing of individuals, evident in changes in melatonin in saliva and urine samples. However, it is unknown whether these changes are also reflected in breast milk from a shift working mother. The aim of this study was to investigate whether maternal circadian rhythm disturbance from shift work impacts the melatonin concentration in breast milk. Materials and Methods: Breast milk and saliva samples were collected from 11 shift working mothers at four timepoints across five consecutive days. This included during their day shift or nonworkdays to act as a control, night shift, subsequent night shifts and postnight shift. Where possible, pre- and postfeed collections were also undertaken. Samples were grouped into four-time intervals: 12-6:30 am, 7-11:30 am, 12-6:30 pm, 7-11:30 pm, and melatonin levels (picogram per milliliter) in the breast milk and saliva samples were analyzed. Results: There was a significant decrease in breast milk melatonin (p = 0.026) at the 12-6:30 am time interval on subsequent night shifts, compared with control days. However, there was no overall time and shift type interaction effect (p = 0.70). In addition, no observed difference in melatonin levels was found in saliva samples, or when comparing pre- and postfeed breast milk. Breast milk melatonin however was found to be significantly higher compared with saliva (p > 0.001), at all but one time interval. Conclusion: The findings suggest that there is a potential effect of maternal circadian rhythm disruption from shift work on breast milk melatonin levels. This is an important step in exploring the role of maternal circadian timing and the effect on breast milk composition. Expansion of this research and exploration of other circadian rhythm misalignment sleep disorders on breast milk is highly recommended.

The sleep, circadian, and cognitive performance consequences of watchkeeping schedules in submariners: A scoping review

Watchkeeping schedules are essential for maintaining submarine operations, but come with human risk factors including, disrupted sleep, circadian misalignment, and cognitive deficits. There is now an emerging literature examining the strengths and weaknesses of submarine watchkeeping schedules trialled in the field and under simulated laboratory conditions. The aim of this scoping review was to summarise this literature. A systematic search of peer-reviewed journal articles and industry reports listed in MEDLINE, PsychINFO, PubMed, Scopus, Embase and Google Scholar undertaken in May 2023 returned 7298 papers. Following screening procedures, 13 studies were identified for inclusion. The findings revealed that sleep was sufficiently preserved regardless of watchkeeping schedule (total sleep time = 5.46-7.89 h), circadian misalignment was greater for non-24 h schedules, and longer off-watch periods were associated with better cognitive performance. Taken together, when comparing between watchkeeping schedules, the present findings suggest that the 4 h-on/8 h-off and 8 h-on/16 h-off schedules may be a good compromise when balancing human risk factors and operational demands. However, submarines are complex and challenging environments to study and there is a need to expand the literature. More research comparing watchkeeping schedules is needed. Future studies should focus on cognitive performance measures, such as problem-solving, prioritisation and executive decision-making to address present shortcomings, and an examination of sleep and circadian countermeasures to assist with adaptation either initiated pre-deployment or by modifying the submarine environment itself should be considered.

Night shift work, sleep duration and endometrial cancer risk: A pooled analysis from the Epidemiology of Endometrial Cancer Consortium (E2C2)

Data on the role of circadian related factors in the etiology of endometrial cancer are scarce. We collected individual data on night shift work or daily sleep duration from 7,207 cases and 22,027 controls participating in 11 studies from the Epidemiology of Endometrial Cancer Consortium (E2C2). Main analyses were performed among postmenopausal women: 6,335 endometrial cancer cases and 18,453 controls. Using individual data, study-specific odd ratios (ORs) and their corresponding 95% confidence intervals (CIs) were estimated with logistic regression and pooled analyses were conducted using random-effects meta-analyses. A non-significant inverse association was observed between endometrial cancer and night shift work (OR=0.89, 95%CI=0.72-1.09; I2=0.0%, Pheterogeneity=0.676). Associations did not vary by shift type (permanent or rotating), or duration of night work. Categorizations of short (<7h) or long (≥9h) sleep duration were not associated with endometrial cancer risk (ORshort=1.02, 95%CI=0.95-1.10; I2=55.3%, Pheterogeneity=0.022; ORlong=0.93, 95%CI=0.81-1.06; I2=11.5%, Pheterogeneity=0.339). No associations were observed per 1-h increment of sleep (OR=0.98, 95%CI=0.95-1.01; I2=46.1%, Pheterogeneity=0.063), but an inverse association was identified among obese women (OR=0.93, 95%CI=0.89-0.98 per 1-h increment; I2=12.7%, Pheterogeneity=0.329). Overall, these pooled analyses provide evidence that night shift work and sleep duration are not strong risk factors for endometrial cancer in postmenopausal women.

Fatigue and fallibility: the perils of prolonged shifts for neonatologists

Sleep deprivation is a major challenge for neonatologists, who face increasing demands in the complex healthcare system. Current neonatal intensive care unit (NICU) schedule models often include extended shifts and overnight call, which can lead to sleep deprivation. This lack of sufficient sleep poses adverse health risks to neonatologists and can impair cognitive function, which increases the risk of medical errors and compromises patient safety. This paper proposes reducing shift durations and implementing policies and interventions to reduce fatigue among neonatologists and improve patient safety. The paper also offers policymakers, healthcare leaders, and NICU physicians valuable insights on potential ways to promote the health of the neonatologist workforce and safety in the NICU.