Methodological aspects of shift-work research

Evaluating the impact of shift work on the risk of cardiometabolic disease: A Mendelian randomization study

BACKGROUND AND AIMS

Evidence is increasingly suggesting that shift work is a risk factor for cardiometabolic disease. However, the causal relationship between shift work and cardiometabolic disease is not yet fully understood. In this study, we employed two-sample Mendelian randomization (MR) to investigate the causal relationship between shift work and the risk of cardiometabolic outcomes.

METHODS AND RESULTS

Genome-wide association study (GWAS) statistics for shift work were obtained from the UK Biobank. Mendelian randomization analyses were conducted to explore the causal effects of shift work on cardiometabolic outcomes, using single-nucleotide polymorphisms (SNPs) as instrumental variables. The results suggested a causal effect between shift work and body mass index, body fat percentage, triglycerides, high-density lipoprotein, type 2 diabetes, hypertension, and cardiorespiratory fitness. After correcting for multiple tests, only body mass index and high-density lipoprotein showed significant associations. No causal effects were found between shift work and overweight, obesity, total cholesterol, low-density lipoprotein, fasting glucose, 2-h glucose, fasting insulin, coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, or ischemic stroke.

CONCLUSION

This MR study provides genetic evidence for a suggestive causal link between shift work and certain cardiometabolic outcomes. Our research may have the significance of providing insight into public hygiene to improve the understanding of shift work and cardiometabolic disease risk. Further experimental studies are needed to confirm our findings.

The Effect of a Healthy Lifestyle Intervention on Shift Workers With Acid Peptic Disease: A Quasi-experimental Study in Karaikal, South India

Acid peptic disease (APD) is the most common health issue among rotational shift workers, including night shifts. Alterations in diet patterns from the routines of life play a key role in the development of APD in this population. This study aims to determine food habits and evaluate the effect of a healthy lifestyle intervention on reducing the frequency of the occurrence of APD among rotational shift workers. A quasi-experimental study was carried out for six months in Karaikal, South India. About 37 employees involved in rotational shift work were recruited consecutively. A healthy lifestyle intervention was implemented, and pre and postintervention data were collected using a pre-tested, semi-structured questionnaire. The McNemar test was employed to assess the pre and postintervention data using SPSS Statistics version 24 (IBM Corp., Armonk, NY, USA). Among 37 shift workers, almost 21 (56.8%) were suffering from heartburn, and about 14 (38%) presented with two symptoms. Before the intervention, 24 (64.9%) workers experienced APD > 28 days after the previous episode. After intervention, a majority of 34 (91.9%) workers experienced APD > 28 days after the previous episode (p-value = 0.002). This highlights the importance of healthy lifestyle modifications in controlling APD among shift workers. This in turn improves the productivity of the workers.

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.

Effects of co-sleeping with a shift worker on sleep, mood and cognition

Objective

Although the negative effects of shift work on workers' sleep and mood are well-known, the effects of shift work on their sleep partners' sleep and mood have rarely been investigated. The current study explored the effects of co-sleeping with a shift worker (SW) on the partner's subjective sleep quality, daytime sleepiness, depressive symptoms, and cognitive disturbances.

Methods

Online sleep and work-environment self-report questionnaires (e.g., including the presence of co-sleepers, work schedules of the co-sleepers, and their work schedules) were administered. The questionnaires also included the Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleepiness Scale (ESS), the Cognitive Failures Questionnaire (CFQ), and the short-term Center for Epidemiologic Studies-Depression scale (CES-D). Participants consisted of co-sleepers of SWs (n = 657), co-sleepers of non-SWs (n = 2186), and solo sleepers (n = 2432).

Results

Significant between-group differences in the PSQI, ESS, CFQ, and CES-D were observed after controlling for age, gender, work shift, and parenting (p < 0.001). Co-sleepers of SWs showed higher PSQI, ESS, CFQ, and CES-D scores than co-sleepers of non-SWs and solo sleepers. Solo sleepers reported significantly higher PSQI and CES-D scores than co-sleepers of non-SWs. The PSQI, ESS, CFQ, and CES-D scores were significantly correlated in all groups. The association between the ESS and PSQI was stronger in co-sleepers of SWs than in solo sleepers. The association between the ESS and CES-D was stronger in co-sleepers of SWs than in solo sleepers.

Conclusions

Co-sleeping with SWs is associated with poor sleep quality, daytime sleepiness, depressive symptoms, and cognitive disturbances in the partner.

Circadian regulation of liver metabolism: experimental approaches in human, rodent, and cellular models

Circadian rhythms are endogenous oscillations with approximately a 24-h period that allow organisms to anticipate the change between day and night. Disruptions that desynchronize or misalign circadian rhythms are associated with an increased risk of cardiometabolic disease. This review focuses on the liver circadian clock as relevant to the risk of developing metabolic diseases including nonalcoholic fatty liver disease (NAFLD), insulin resistance, and type 2 diabetes (T2D). Many liver functions exhibit rhythmicity. Approximately 40% of the hepatic transcriptome exhibits 24-h rhythms, along with rhythms in protein levels, posttranslational modification, and various metabolites. The liver circadian clock is critical for maintaining glucose and lipid homeostasis. Most of the attention in the metabolic field has been directed toward diet, exercise, and rather little to modifiable risks due to circadian misalignment or disruption. Therefore, the aim of this review is to systematically analyze the various approaches that study liver circadian pathways, targeting metabolic liver diseases, such as diabetes, nonalcoholic fatty liver disease, using human, rodent, and cell biology models.NEW & NOTEWORTHY Over the past decade, there has been an increased interest in understanding the intricate relationship between circadian rhythm and liver metabolism. In this review, we have systematically searched the literature to analyze the various experimental approaches utilizing human, rodent, and in vitro cellular approaches to dissect the link between liver circadian rhythms and metabolic disease.

Comparing shift work tolerance across occupations, work arrangements, and gender

BACKGROUND

There are individual differences in shift work tolerance; however, we lack knowledge about how this is experienced across different occupations, sex and shift types.

AIMS

The aim was to describe and investigate shift work tolerance, and individual differences in shift work tolerance, in two occupations, between men and women and between day/evening workers and rotating shift workers.

METHODS

Cross-sectional questionnaire study. The sample was comprised of 315 retail workers and 410 police employees.

RESULTS

Shift work tolerance was higher among police employees compared to retail workers, among men compared to women, and among day workers compared to evening/rotating shift workers. The difference was larger between occupations than between sex and shift type. Evening workers had more symptoms of shift work intolerance than rotating shift workers. Neuroticism and autonomy were related to all symptoms of shift work tolerance among retail workers, but not police employees.

CONCLUSIONS

It is important to consider the type of occupation and the work context when tailoring work arrangements to the individual.

Association between shift work in early pregnancy, snacking, and inappropriate weight gain during pregnancy: The Japan Environment and Children's Study

OBJECTIVES

This study aimed to investigate the relationship between night shifts and snacking behaviors during pregnancy using Japanese maternal-infant longitudinal data from a large-scale study.

METHODS

This study used the Japan Environment and Children's Study dataset jecs-ta-20190930, released in October 2019. After simple analysis using analysis of variance and multiple comparisons, crude odds ratios (cOR) and adjusted odds ratios (aORs) were calculated. To evaluate eating habits, we examined habitual fast food and snacks (e.g., potato chips, corn puffs and tortilla chips) consumption, midnight snacks, and regular missing breakfast.

RESULTS

There was no significant association between inappropriate weight gain during pregnancy and night shift work in early pregnancy. The aOR for consuming snacks more than once a week after noticing pregnancy for shift workers was 1.34 (95% confidence interval 1.27-1.41; p < 0.001) compared with worker without night shiftwork. The aOR for shift workers consuming fast food more than three times a week during pregnancy was 1.40 (95% confidence interval 0.79-2.33; p > 0.05).

CONCLUSIONS

Pregnant night shift workers did not show excessive weight gain but had an increased frequency of consumption of snack foods compared with pregnant dayshift workers.

Fatigue and somatization in shift-workers: Effects of depression and sleep

OBJECTIVE

We investigated the differences in fatigue and somatization between shift and non-shift workers and explored the effects of sleep and depression on fatigue and somatization in shift workers.

METHODS

In total, 4543 shift workers and 2089 non-shift workers completed self-reported questionnaires. The Center for Epidemiologic Studies Depression Scale (CESD), Pittsburgh Sleep Quality Index (PSQI), Fatigue Severity Scale (FSS), and Somatization subscale of the Symptom Checklist 90-item version (SCL-SOM) were used to measure depression, sleep quality, fatigue, and somatization, respectively. Fatigue and somatization were compared between shift and non-shift workers after controlling for different sets of covariates.

RESULTS

Compared to non-shift workers, shift workers reported higher FSS (mean difference: 2.19 ± 0.30, p < 0.01) and SCL-SOM (mean difference: 1.77 ± 0.21, p < 0.01) scores after controlling for age, gender, presence of medical illness, occupational category, monthly income, length of service, and weekly working hours. The between-group difference in FSS score was no longer significant after additionally controlling for CES-D (p = 0.15) or PSQI (p = 0.18). The between-group difference in SCL-SOM score showed only non-significant trends after additionally controlling for CES-D (p = 0.09) or PSQI (p = 0.07). The group difference in SCL-SOM scores disappeared after controlling for both CES-D and PSQI scores (p = 0.99).

CONCLUSIONS

Shift workers had higher fatigue and somatization levels than non-shift workers and the group difference was associated with disturbed sleep and depressed mood in shift workers.

Association between shift work and serum homocysteine level in female electronic manufacturing services workers

Background

Shift work has been shown to increase the risk of cardiovascular disease (CVD) based on several evidences. The classic risk factors of CVD include age, hypertension, smoking, obesity and diabetes. Recently, the serum homocysteine level has been reported to be a valuable indicator of CVD risk. This study aimed to determine the variation in serum homocysteine level as a cardiovascular risk indicator among female workers according to shift work.

Methods

The data of regular health examination of workers at an electronic manufacturing services company in Yeongnam region, South Korea in 2019 were examined in this study. The investigation was based on a cross-sectional study conducted on 697 female workers (199 day workers and 498 shift workers). The sociodemographic and biochemical characteristics were compared between day workers and shift workers. Through a logistic regression analysis, the odds ratio (OR) of the increased serum homocysteine level in relation to shift work was determined.

Results

Compared to female day workers, female shift workers showed significantly higher level of serum homocysteine (8.85 ± 2.16 vs. 9.42 ± 2.04 μmol/mL; p = 0.001). The OR of day workers against shift workers was 1.81 (95% confidence interval [CI]: 1.25-2.63). With the adjustment of variables that may influence the level of serum homocysteine, the adjusted OR was 1.68 (95% CI: 1.09-2.60).

Conclusions

The serum homocysteine level was significantly higher in shift workers than in day workers. It is thus likely to be a useful predictor of CVD in shift workers.

Health, Occupational Stress, and Psychosocial Risk Factors in Night Shift Psychiatric Nurses: The Influence of an Unscheduled Night-Time Nap

BACKGROUND

Occupational stress and shift work (including night shift work) are associated with physical and psychological health consequences in healthcare providers in general and those working in psychiatric establishments in particular. The aim of this study was to assess the impact of occupational risk factors and unscheduled night-time naps on self-reported health disorders among nurses working in a French psychiatric hospital.

METHODS

We performed a 12-month observational field study of experienced nurses working at Philippe Pinel Psychiatric Hospital (Amiens, France) between September 2018 and September 2019. A comparative descriptive study of two groups of nurses who filled out a questionnaire on health and occupational stress was performed: nurses working permanently on the night shift (the night shift group, who took unscheduled naps), and nurses rotating weekly between morning and afternoon shifts (the day shift group).

RESULTS

The night and day shift groups comprised 53 and 30 nurses, respectively. There were no intergroup differences in health disorders, sleep quality, occupational stress, and risk factor perception. Correlation analyses showed that in the day shift group, a low level of support from supervisors was associated with elevated levels of distress, anxiety, and gastrointestinal disorders. In the night shift group, a greater overall work load was associated with elevated levels of anxiety and distress. These findings indicated that the nurses on the night shift had adapted well to their working conditions.

CONCLUSIONS

An organizational strategy including an unscheduled night-time nap might improve health among night shift nurses.

Association between shift work and inflammatory markers in workers at an electronics manufacturing company

Background

Shift work is known to be associated with cardiovascular disease (CVD). It has been found that inflammatory reactions are involved in the onset and progression of CVD. Therefore, the purpose of this study was to investigate the association between shift work and inflammatory markers.

Methods

Among workers at an electronics manufacturing company, 2,329 workers who had a health checkup from January 2019 to December 2019 were targeted. The general and biochemical characteristics of daytime workers and shift workers were compared through the Independent-test and the χ² test. Through multiple linear regression analysis, the association with shift work and inflammatory markers was investigated. Through multiple logistic regression analysis, the association with shift work and high inflammatory markers.

Results

The mean total leukocytes, neutrophils, monocytes, lymphocytes of shift workers were significantly higher than those of daytime worker. The mean high-sensitivity C-reactive protein (hs-CRP) of shift workers was also higher than that of daytime workers but not significantly. In multiple linear regression, shift work was associated with increase of total leukocyte count (β = 0.367, p < 0.001) and hs-CRP (β = 0.140, p = 0.005) after adjusting for all variables. In multiple logistic regression analysis, shift work showed 2.27 times risk of high leukocyte count and 1.8 times risk of high hs-CRP level compared to daytime work after adjusting for all variables.

Conclusions

This study confirmed that shift work is associated with high inflammatory markers. Considering that high inflammatory markers is independent indicator of CVD, the association between shift work and high inflammatory markers may help to understand the CVD risk of shift workers.

Describing economic benefits and costs of nonstandard work hours: A scoping review

BACKGROUND

The benefits of nonstandard work hours include increased production time and the number of jobs. While for some sectors, such as emergency services, around-the-clock work is a necessary and critical societal obligation, work outside of traditional daytime schedules has been associated with many occupational safety and health hazards and their associated costs. Thus, organizational- and policy-level decisions on nonstandard work hours can be difficult and are based on several factors including economic evaluation. However, there is a lack of systematic knowledge of economic benefits and costs associated with these schedules.

METHODS

We conducted a scoping review of the methodology and data used to examine the economic benefits and costs of nonstandard work hours and related interventions to mitigate risks.

RESULTS

Ten studies met all our inclusion criteria. Most studies used aggregation and analysis of national and other large datasets. Costs estimated include health-related expenses, productivity losses, and projections of future loss of earnings. Cost analyses of interventions were provided for an obstructive sleep apnea screening program, implementation of an employer-based educational program, and increased staffing to cover overtime hours.

CONCLUSIONS

A paucity of studies assess nonstandard work hours using economic terms. Future studies are needed to expand economic evaluations beyond the employer level to include those at the societal level because impacts of nonstandard work go beyond the workplace and are important for policy analysis and formulation. We pose the opportunity for researchers and employers to share data and resources in the development of more analyses that fill these research gaps.

Shift Work Disorder Index: initial validation and psychosocial associations in a sample of nurses

STUDY OBJECTIVES

Shift work is common yet does not always result in Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5)-defined shift work sleep disorder (SWD). This study reports on the reliability and validity of the DSM-5 informed Shift Work Disorder Index (SWDI), the presence of probable SWD in nurses, and demographic, sleep, and psychosocial correlates.

METHODS

Nurses (n = 454) completed the SWDI, psychosocial, and demographic questionnaires. Of the sample, n = 400 completed 14 days of sleep diaries, actigraphy, and additional questionnaires.

RESULTS

The global SWDI demonstrated excellent internal consistency (α = .94), as well as good convergent and divergent validity in the nurse sample. Thirty-one percent of nurses were past-month shift workers, with 14% (ie, 44% of shift workers) having probable SWD based on SWDI. Nurses who worked shift work and/or met SWD criteria were more likely to be younger and unmarried and less likely to have children than day workers and reported greater evening chronotype, insomnia, nightmares, and sleep-related impairment, greater depression, anxiety, posttraumatic stress, and perceived stress symptoms, as well as later and more variable sleep midpoint (actigraphy), shorter sleep duration (actigraphy, diaries), and lower sleep efficiency (diaries).

CONCLUSIONS

The SWDI is an efficient and valid self-report assessment of DSM-5-defined SWD. Shift work and/or SWD were prevalent and associated with worse sleep and psychosocial health, particularly among nurses with probable SWD.

CITATION

Taylor DJ, Dietch JR, Wardle-Pinkston S, et al. Shift Work Disorder Index: initial validation and psychosocial associations in a sample of nurses. J Clin Sleep Med. 2022;18(10):2339-2351.

Effects of 90 Min Napping on Fatigue and Associated Environmental Factors among Nurses Working Long Night Shifts: A Longitudinal Observational Study

For nurses working long night shifts, it is imperative that they have the ability to take naps to reduce fatigue, and that an appropriate environment is prepared where such naps can be taken. We verified the effects of 90 min napping on fatigue and the associated factors among nurses working 16-h night shifts. We investigated 196-night shifts among 49 nurses for one month. Wearable devices, data logging devices, and questionnaires were used to assess nap parameters, fatigue, and environmental factors such as the napping environment, ways of spending breaks, and working environment. Nurses who nap at least 90 min on most night shifts had more nursing experience. Multivariable logistic regression analysis showed that the environmental factors significantly associated with total nap duration (TND) ≥ 90 min were noise, time spent on electronic devices such as cellphones and tablets during breaks, and nap break duration. The night shifts with TND ≥ 90 min showed lower drowsiness after nap breaks and less fatigue at the end of night shift compared to those with TND < 90 min. Nurses and nursing managers should recognize the importance of napping and make adjustments to nap for at least 90 min during long night shifts.

Determinants of Sleep Disorders and Occupational Burnout among Nurses: A Cross-Sectional Study

Background: The aim of the study was to assess the determinants of the sleep disorders that occur among nurses working in a shift system by assessing the influence of sociodemographic factors, the impact of shift work, and the occurrence of occupational burnout. Methods: The study included 300 nurses who work shifts in the Silesian Region (Poland). The research was conducted using standardized research tools: the Karolinska Sleepiness Scale (KSS), the Epworth Sleepiness Scale (ESS), the Athens Insomnia Scale (AIS), and the Maslach Burnout Inventory (MBI). Results: Among the sociodemographic factors, in the KSS analysis, sleep disorders were most common in men (CI: 0.038; p < 0.001), in divorced individuals (CI: 1.436; p = 0.045), and in individuals who were overweight (CI: 1.927; p = 0.026). Multiple linear regression showed that sleep disorders (p < 0.001) were an independent predictor of MBI among nurses who worked shifts. Conclusions: Sleep disturbances affect the burnout of nurses who work shifts.

Night-shift work is associated with increased susceptibility to SARS-CoV-2 infection

Night-shift workers experience disturbances of their circadian rhythm and sleep, which may make them more susceptible to infectious diseases. Therefore, we studied whether night-shift workers are at higher risk of testing positive for SARS-CoV-2 infection than day workers. In this prospective study, data were used from 20 questionnaire rounds of the Dutch Lifelines COVID-19 cohort that was initiated in March 2020. In the different questionnaire rounds, 2285 night-shift workers and 23,766 day workers reported whether they had tested positive for SARS-CoV-2. Cox proportional hazards regression models adjusted for demographic, work, and health covariates were used to compare SARS-CoV-2 incidence between night-shift and day workers. From March 2020-January 2021, 3.4% of night-shift workers and 2.2% of day workers reported to have tested positive for SARS-CoV-2 (p < .001). After adjustment for covariates, night-shift workers had a 37% higher risk of testing positive for SARS-CoV-2 (hazard ratio: 1.37, 95% confidence interval: 1.05-1.77). In this study, we show that night-shift workers were more likely to test positive for SARS-CoV-2 than day workers, which adds to the growing evidence that night-shift work may influence the complex processes involved in infection susceptibility. Further mechanistic insight is needed to understand the relation between night-shift work and (SARS-CoV-2) infection susceptibility.

Neurocognitive impairment in night and shift workers: a meta-analysis of observational studies

OBJECTIVE

Shift work is an essential element of modern labour, ensuring ideal conditions of service for today's economy and society. Despite the beneficial properties, its impact on the neurobehavioural performance of exposed subjects remains controversial. This meta-analysis aimed to provide the first summarising effects regarding the association between shift work exposure and different cognitive functions.

METHODS

A literature search was performed using the databases PubMed, PsyINFO, PsyARTICLES, MedLine, PsycNET and Scopus including eligible studies up to April 2021 that compared shift workers with non-shift workers regarding neurobehavioural performance tests. We carried out a random-effects model using Hedges' g as a meta-analytical effect size with a restricted likelihood estimator to summarise the mean differences between the exposure group and controls. Positive effect sizes indicate higher performance for non-shift workers. The heterogeneity of effect sizes was addressed by sensitivity analysis using funnel plots, Egger's tests, p-curve analysis, meta-regressions and subgroup analysis.

RESULTS

We included 18 studies resulting in a total sample of 18 802 participants and 37 effect sizes concerning six different neurobehavioural outcomes. Our results showed significantly worse performance in shift workers compared with non-shift workers in the following cognitive functions with g (95% CI): processing speed 0.16 (0.02 to 0.30), working memory 0.28 (0.51 to 0.50), psychomotor vigilance 0.21 (0.05 to 0.37), cognitive control 0.86 (0.45 to 1.27) and visual attention 0.19 (0.11 to 0.26).

CONCLUSIONS

We provide the first meta-analytical findings that associate shift work with decreased cognitive performance in processing speed, working memory, psychomotor vigilance, cognitive control and visual attention.

Rotating night shift work, sleep duration and elevated gamma-glutamyl transpeptidase among steelworkers: cross-sectional analyses from a Chinese occupational cohort

OBJECTIVES

This study aimed to evaluate the separate and combined effects of rotating night shift work and lifestyle factors with elevated gamma-glutamyl transpeptidase (GGT) among steelworkers.

DESIGN, SETTING AND PARTICIPANTS

This cross-sectional study used the baseline information from a Chinese occupational cohort. The in-service workers of the production department of Tangsteel Company who participated in the occupational health examination in Tangshan from February to June 2017 were selected as the research objects.

MAIN OUTCOME MEASURES

The separate and combined effects of rotating night shift work and lifestyle factors with elevated GGT among steelworkers.

RESULTS

The information of 7031 subjects from the production department of Tangsteel Company was analysed. Results showed that the current shift workers and the workers with the duration of night shifts>19 years, the cumulative number of night shifts>1774 nights, the average frequency of night shifts≤7 nights/month and the average frequency of night shifts>7 nights/month had elevated odds of elevated GGT, compared with those who never worked night shifts, and ORs, (95% CIs) were 1.39, (1.10 to 1.75), 1.46, (1.15 to 1.86), 1.46, (1.15 to 1.85), 1.34, (1.04 to 1.73) and 1.37, (1.09 to 1.74) after adjustment for potential confounders. The independent effect of shorter sleep duration (<7 hours/day) on elevated GGT was not statistically significant. Among workers who had shorter sleep duration, the association between rotating night shift work and elevated GGT was statistically significant, but no associations were found among workers with the sleep duration of ≥7 hours/day. In addition, other lifestyle factors affected the association between rotating night shift work and elevated GGT.

CONCLUSIONS

Rotating night shift work is associated with elevated GGT among steelworkers. In particular, the effect of rotating night shift work on elevated GGT was affected by sleep duration and other lifestyle factors.

Guiding principles for determining work shift duration and addressing the effects of work shift duration on performance, safety, and health: guidance from the American Academy of Sleep Medicine and the Sleep Research Society

CITATION

Risks associated with fatigue that accumulates during work shifts have historically been managed through working time arrangements that specify fixed maximum durations of work shifts and minimum durations of time off. By themselves, such arrangements are not sufficient to curb risks to performance, safety, and health caused by misalignment between work schedules and the biological regulation of waking alertness and sleep. Science-based approaches for determining shift duration and mitigating associated risks, while addressing operational needs, require: (1) a recognition of the factors contributing to fatigue and fatigue-related risks; (2) an understanding of evidence-based countermeasures that may reduce fatigue and/or fatigue-related risks; and (3) an informed approach to selecting workplace-specific strategies for managing work hours. We propose a series of guiding principles to assist stakeholders with designing a shift duration decision-making process that effectively balances the need to meet operational demands with the need to manage fatigue-related risks.

Sleep medication and melatonin use among Norwegian nurses - A cross-sectional study

Aim

To estimate the prevalence of sleep medication and melatonin use among nurses and to assess if factors related to work, sleep or mental health, were associated with such use.

Design

A cross‐sectional study.

Methods

A questionnaire survey including 2,798 Norwegian nurses. Associations were estimated using a modified Poisson regression model.

Results

In total, 7.5%, 4.6% and 2.0% of the nurses included in the present study reported prescribed sleep medication, over‐the‐counter sleep medication or melatonin use in the last year, respectively. Short sleep duration, sleep problems and psychological conditions were strongly associated with both prescribed and over‐the‐counter sleep medication use. Nurses who worked more than 60 night shifts in the last year were at increased risk of sleep medication use.

Guiding principles for determining work shift duration and addressing the effects of work shift duration on performance, safety, and health: guidance from the American Academy of Sleep Medicine and the Sleep Research Society

Risks associated with fatigue that accumulates during work shifts have historically been managed through working time arrangements that specify fixed maximum durations of work shifts and minimum durations of time off. By themselves, such arrangements are not sufficient to curb risks to performance, safety, and health caused by misalignment between work schedules and the biological regulation of waking alertness and sleep. Science-based approaches for determining shift duration and mitigating associated risks, while addressing operational needs, require: (1) a recognition of the factors contributing to fatigue and fatigue-related risks; (2) an understanding of evidence-based countermeasures that may reduce fatigue and/or fatigue-related risks; and (3) an informed approach to selecting workplace-specific strategies for managing work hours. We propose a series of guiding principles to assist stakeholders with designing a shift duration decision-making process that effectively balances the need to meet operational demands with the need to manage fatigue-related risks.

The mediating role of unhealthy behavior in the relationship between shift work and perceived health

Background

Little is known about the relationship between shift work and perceived health, including potential underlying mechanisms such as unhealthy behaviors. The aim of this study was to investigate whether unhealthy behaviors mediate the relationship between shift work and perceived mental and physical health, taking into account potential differences by level of education.

Methods

Data from 1633 workers participating in the Doetinchem Cohort Study during 1995–2016 were used. Being engaged in shift work was determined at 1 year preceding the assessment of health behaviors. Mental and physical health were assessed after 5 years of follow-up by the 5-item Mental Health Inventory and the physical functioning scale of the 36-item Short Form Health Survey. Smoking, physical inactivity, alcohol consumption, and overweight were considered as potential mediators and education was treated as moderator. Moderated mediation analyses using generalized estimated equations were performed.

Results

Shift work was not statistically significantly related to either mental or physical health. Despite this, statistically significant mediation effects of smoking (Beta − 0.09; 95% Confidence Interval − 0.20 - -0.01, respectively B -0.09; 95%CI -0.21 - -0.01) and physical inactivity (B 0.11; 95%CI 0.03–0.23, respectively B 0.08; 95%CI 0.01–0.18) were found in the relationship between shift work and mental or physical health. Direct and indirect effects outweighed each other in the relationship between shift work and mental health, since the direction of these effects was opposite. The relationship between shift work, unhealthy behavior, and health was not different by educational level.

Conclusion

Shift workers did not report lower mental or physical health than non-shift workers. Though mediation effects of unhealthy behavior were observed in the relationship between shift work and perceived health, these small effects had minor public health relevance.

Work Shift, Lifestyle Factors, and Subclinical Atherosclerosis in Spanish Male Workers: A Mediation Analysis

(1) Background: Working night shifts has been associated with altered circadian rhythms, lifestyle habits, and cardiometabolic risks. No information on the potential association of working shift and the presence of atherosclerosis is available. The aim of this study was to quantify the association between different work shifts and the presence of subclinical atherosclerosis objectively measured by imaging. (2) Methods: Analyses were conducted on the baseline data of the Aragon Workers Health Study (AWHS) cohort, including information on 2459 middle-aged men. Categories of shift work included central day shift, rotating morning-evening or morning-evening-night shift, and night shift. The presence of atherosclerotic plaques was assessed by 2D ultrasound in the carotid and femoral vascular territories. Multivariable logistic models and mediation analysis were conducted to characterize and quantify the association between study variables. (3) Results: Participants working night or rotating shifts presented an overall worse cardiometabolic risk profile, as well as more detrimental lifestyle habits. Workers in the most intense (morning-evening-night) rotating shift presented higher odds of subclinical atherosclerosis (odds ratio: 1.6; 95% confidence interval: 1.12 to 2.27) compared to workers in the central shift, independently of the presence of lifestyle and metabolic risk factors. A considerable (21%) proportion of this association was found to be mediated by smoking, indicating that altered sleep-wake cycles have a direct relationship with the early presence of atherosclerotic lesions. (4) Conclusions: Work shifts should be factored in during workers health examinations, and when developing effective workplace wellness programs.

Prevalence of Shift Work Disorder: A Systematic Review and Meta-Analysis

Objectives: No systematic review or meta-analysis concerning the prevalence of shift work disorder (SWD) has been conducted so far. The aim was thus to review prevalence studies of SWD, to calculate an overall prevalence by a random effects meta-analysis approach and investigate correlates of SWD prevalence using a random-effects meta-regression.

Methods: Systematic searches were conducted in ISI Web of Science, PsycNET, PubMed, and Google Scholar using the search terms “shift work disorder” and “shift work sleep disorder.” No restrictions in terms of time frame were used. Included studies had to present original data on the prevalence of SWD in an occupational sample published in English. A total of 349 unique hits were made. In all, 29 studies were finally included from which two authors independently extracted data using predefined data fields. The meta-regression included four predictors (diagnostic criteria, study country, type of workers, and sample size).

Results: The overall prevalence of SWD was 26.5% (95% confidence interval = 21.0–32.8). Cochran Q was 1,845.4 (df = 28, p < 0.001), and the I² was 98.5%, indicating very high heterogeneity across the observed prevalence estimates. Diagnostic criteria (International Classification of Sleep Disorders-2 = 0, International Classification of Sleep Disorders-3 = 1) and sample size were inversely related to SWD prevalence.

Conclusions: The prevalence of SWD was high across the included studies. The between-study disparity was large and was partly explained by diagnostic criteria and sample size. In order to facilitate comparative research on SWD, there is a need for validation and standardization of assessment methodology as well as agreement in terms of sample restrictions.

Short sleep duration and high exposure to quick returns are associated with impaired everyday memory in shift workers

PURPOSE

To investigate the relationship between self-reported everyday memory problems the last month, and: (a) shift work schedule, (b) night shifts and quick returns worked the last year, and (c) sleep duration the last month.

METHODS

In all, 1,275 nurses completed the Everyday Memory Questionnaire - revised, and answered questions about shift work exposure and sleep duration. We performed multiple linear regression analyses with memory score as dependent variable, and the shift work exposure variables as well as sleep duration as predictors, while adjusting for potential confounders.

FINDINGS

High exposure to quick returns (β = .10, p < .05) and short sleep duration (β = .10, p < .05) were both positively associated with memory problems, whereas shift work schedule, long sleep duration, night shift exposure, and low and moderate exposure to quick returns were not.

DISCUSSION

Frequent insufficient time for rest between shifts as well as short sleep was associated with poorer everyday memory.

Good Sleep Quality and Progressive Increments in Vigilance During Extended Night Shifts: A 14-Day Actigraphic Study in Underground Miners

OBJECTIVE

Assess the change in sleep and vigilance of underground miners during long periods of extended shifts.

METHODS

Seventy miners worked 14 consecutive 12-hour day and/or night shifts. Also, they wore an actigraph and completed a visual analog scale for vigilance four times per shift. Linear regression models with mixed effects were used.

RESULTS

Sleep efficiency was higher during day shifts than during night shifts (86,5 vs 85.5, P < 0.05) but sleep duration did not differ (6:34 vs 6:44, n.s.). Mean vigilance level at Time 3 (02h00) was significantly lower than that at Time 1 (19h00) during the first 10 night shifts whereas mean vigilance level at Time 4 (05h30) remained significantly lower for the 14 night shifts.

CONCLUSIONS

Underground miners exhibit good sleep quality despite evidence of limited circadian adaptation in terms of nighttime vigilance.

The effects of bright light treatment on subjective and objective sleepiness during three consecutive night shifts among hospital nurses - a counter-balanced placebo-controlled crossover study

Objectives The objective was to investigate effects of timed bright light treatment on subjective and objective measures of sleepiness during three consecutive night shifts among hospital nurses. Methods Thirty-five nurses were exposed to bright light (10,000 lux) and red dim light (100 lux) during three consecutive night shifts in a counter-balanced crossover trial lasting nine days, which included three days before and three days after the three night shifts. Light exposure for 30 minutes was scheduled between 02:00-03:00 hours on night 1, and thereafter delayed by one hour per night in order to delay the circadian rhythm. Subjective sleepiness was measured daily (heavy eyelids, reduced performance) and every second hour while awake (Karolinska Sleepiness Scale, KSS). Objective sleepiness (Psychomotor Vigilance Task, PVT) was measured at 05:00 hours during each night shift. Beyond nocturnal light exposure on the night shifts, no behavioral restrictions or recommendations were given at or off work. Results Bright light treatment significantly reduced heavy eyelids during night shifts. However, results on KSS and PVT were unaffected by bright light. There were no differences in subjective sleepiness during the three days following the night shifts. Conclusions This bright light treatment protocol did not convincingly reduce sleepiness among nurses during three consecutive night shifts. Nor did bright light impede the readaptation back to a day-oriented rhythm following the night shift period. Too few consecutive night shifts, inappropriate timing of light, and possible use of other countermeasures are among the explanations for the limited effects of bright light in the present study.

The Association Between Shift Work and Immunological Biomarkers in Nurses

Objectives: Shift work is associated with several negative health effects. The underlying pathophysiological mechanisms are unclear, but low-grade inflammation has been suggested to play a role. This project aimed to determine whether levels of immunological biomarkers differ depending on work schedule, self-reported sleep duration, self-reported sleep quality, and presence of shift work disorder (study 1). Furthermore, we aimed to determine whether these biomarkers differ after a night of sleep vs. at the end of a night or a day shift (study 2).

Methods: In study 1, 390 nurses provided blood samples after a night of sleep with the dried blood spot method. In study 2, a subset of 55 nurses also provided blood samples after a day shift and after a night shift. The following biomarkers were measured: interleukin-1alpha, interleukin-1beta, interleukin-4, interleukin-6, interleukin-8, interleukin-10, interleukin-13, monocyte chemoattractant protein-1, interferon-gamma, and tumor necrosis factor-alpha. Multiple linear regressions with adjustment for age, sex and body mass index (study 1) and ANOVAs with repeated measures (study 2) were conducted.

Results: In study 1, neither work schedule, number of night shifts, number of quick returns (<11 h between consecutive shifts), sleep duration, poor sleep quality, nor shift work disorder were systematically associated with most of these biomarkers. Compared with day only work, day-evening work was associated with higher levels of IL-1alpha and IL-13, quick returns were associated with higher levels of IL-1beta and MCP-1, short sleep duration (<6 h) was associated with lower levels of IL-1beta and higher levels of TNF-alpha, and long sleep duration (8+ h) was associated with higher levels of IL-13. In study 2, IL-1beta levels were higher (large effect size) both after a day shift (14% increase) and a night shift (75% increase) compared with levels after a night of sleep. Similarly, TNF-alpha levels were higher (moderate-large effect size) after a day shift (50% increase) compared to after a night of sleep. In contrast, MCP-1 levels were lower (large effect size) both after a day shift (22% decrease) and a night shift (12% decrease) compared with after a night of sleep.

Conclusions: We found some indications that shift work influenced immunological biomarkers. The results should be interpreted with caution due to limitations, e.g., related to the sampling procedure and to low levels of biomarkers in the blood samples.

Night work, mortality, and the link to occupational group and sex

Objective:

Night shifts are associated with several major diseases. Mortality has been studied only to a limited extent, and the association with night shifts remains unclear. The purpose of the present study was to investigate the association between duration of night shift exposure and mortality in a large sample from the Swedish Twin Registry (the SALT cohort).

Methods:

Cox proportional hazards regression models were used to analyze the data (N=42 731) over a follow-up period of 18 years, with years of night shift work as the exposure variable and adjustment for lifestyle factors and age, and stratification on gender and occupational group.

Results:

The hazard ratio (HR) for “ever” night shifts for total mortality was 1.07 [95% confidence interval (CI) 1.01–1.15] but 1.15 (95% CI 1.07–1.25) for longer exposure (>5 years). Also, HR for cause-specific mortality due to cardiovascular disease was significant, with higher HR for longer night shift exposure. Mortality due to cancer was significant for longer exposure only. White-collar workers showed significant HR for longer exposure. In particular, male white-collar workers showed a significant HR, with a highest value for longer exposure [HR 1.28 (95% CI 1.09–1.49)]. Heredity did not influence the results significantly.

Conclusions:

Long duration of exposure to night shift work is associated with increased mortality, particularly in male white-collar workers. The lack of effects of accumulated exposure suggests that the results should be interpreted with caution.

Prevalence and Recent Trends in Exposure to Night Shiftwork in Canada

Objectives

Night shiftwork has been linked to various health outcomes. Knowing where and to what extent workers are exposed to this type of shiftwork can help prioritize areas for intervention and further study. This study describes recent estimates of exposure to night shiftwork in Canada for 2011, and temporal trends from 1997 to 2010.

Methods

Estimates by occupation, industry, province, and sex were calculated using data from the Survey of Labour and Income Dynamics (SLID) from 1996 to 2011. Workers who reported rotating or regular night shifts were classified as exposed to shiftwork involving nights, while those reporting other types of shiftwork, outside of regular daytime and evening shifts, were classified as possibly exposed. Results, with 97.5% confidence intervals (CIs), were summarized for three exposure categories: exposed workers, possibly exposed workers, and evening shift workers. Trends in 3-year rolling averages were described.

Results

In 2011, approximately 1.8 million Canadians (97.5% CI, 1.7–1.8 million), or 12% of the working population (97.5% CI, 11–12%), were exposed to night shiftwork; 45% were female. An additional 2.6 million were possibly exposed (97.5% CI, 2.5–2.7 million workers), and 745 000 worked evening shifts (97.5% CI, 701 000–792 000). This amounts to 17% (97.5% CI, 17–18%) and 4.9% (97.5% CI, 4.6–5.2%) of the labour force, respectively. Industries with the highest prevalence were accommodation and food services (20%; 97.5% CI, 18–22%), forestry, fishing, mining, oil, and gas (19%; 97.5% CI, 16–23%), and healthcare and social assistance (18%; 97.5% CI, 17–19%). By occupation, the highest prevalence of exposure was in occupations in protective services (37%; 97.5% CI, 32–42%), professional occupations in health (35%; 97.5% CI, 32–39%), and machine operators and assemblers in manufacturing (24%; 97.5% CI, 22–28%). The overall number of exposure workers increased by 29% from 1997 to 2010, but the overall proportion remained relatively the same (11% and 12%, respectively). The proportion of female workers exposed increased by 2%.

Conclusions

These estimates characterize exposure to night shiftwork in Canada. Continued collection of shiftwork data, with greater detail on scheduling, workplace and personal factors, is needed for high-quality surveillance and investigations of shiftwork and health.

The longitudinal association between shift work and headache: results from the Danish PRISME cohort

PURPOSE

We investigated the effect of shift work on headache. Furthermore, we investigated whether the association between shift work and headache was explained by potential mediators in terms of perceived stress, poor sleep and health behaviors.

METHODS

In this longitudinal study, we used questionnaire data (collected in 2007 and 2009) from civil servants and hospital employees from the PRISME study. 2952 individuals were available for the analyses of shift work and headache and 2272 individuals were available for the analyses of shift work and migraine. Headache was operationalized as the participants' experience of "being bothered by headache during the past 4 weeks". Migraine was operationalized as "ever being diagnosed with migraine by a medical doctor". We used binary logistic regression to compare shift workers with permanent day workers and adjusted for socio-demographic factors. In a subsequent step, we adjusted for potential mediators.

RESULTS

We found higher odds of unspecific headache (OR = 1.25; 95% CI 1.02-1.54) and migraine (OR = 1.72; 95% CI 1.04-2.86) among shift workers compared with day workers. Our results suggest that the effect of shift work on headache and migraine differ between men and women. Inclusion of potential mediators in the analyses did not attenuate the associations.

CONCLUSION

Shift workers have higher risk of reporting being bothered by headache as well as reporting being diagnosed with migraine. Future research is needed to disentangle the underlying mechanisms with the aim of reducing headache related to occupational exposures.

Pain complaints are associated with quick returns and insomnia among Norwegian nurses, but do not differ between shift workers and day only workers

PURPOSE

To determine whether common work schedule characteristics among Norwegian nurses were associated with subjective pain complaints.

METHODS

A cross-sectional study in a sample of 1585 nurses, part of the longitudinal questionnaire-based cohort project 'Survey of Shift work, Sleep and Health' (SUSSH). Pain from six regions were assessed: 'headache', 'neck/shoulder/upper back', 'upper extremities', 'lower back', 'lower extremities', and 'abdomen'. Logistic and negative binomial regression (adjusted for age, sex, percentage of full-time equivalent, marital status and children living at home) were conducted where work schedule, number of night shifts last year, number of quick returns (QR) last year (< 11 h between shifts) and insomnia were predictors of localized pain, widespread pain and number of pain sites.

RESULTS

Localized pain, widespread pain and number of pain sites were associated with insomnia (OR 2.06, 95% CI 1.66-2.55, OR 2.14, 95% CI 1.47-3.09, IRR 1.70, 95% CI 1.51-1.91, respectively). Work schedule and number of night shifts worked last year were not associated with any of the three pain measures. Number of QRs worked last year tended to be associated with number of pain sites.

CONCLUSION

The study did not support the hypothesis that non-daytime work schedules are associated with pain complaints. Neither was there support for the hypothesis linking number of night shifts, or the number of QRs, to pain complaints. Future studies should aim to determine the association between QRs and pain in more detail. Pain complaints were associated with insomnia.

Shift Work and Lifestyle Factors: A 6-Year Follow-Up Study Among Nurses

Objectives: To evaluate different work schedules, short rest time between shifts (quick returns), and night shift exposure for their possible adverse effects on different lifestyle factors in a 6-year follow-up study.

Methods: Data stemmed from “The Survey of Shiftwork, Sleep and Health,” a cohort study of Norwegian nurses started in 2008/9. The data analyzed in this sub-cohort of SUSSH were from 2008/9 to 2015 and consisted of 1,371 nurses. The lifestyle factors were: Exercise (≥1 h/week, <1 h/week), caffeine consumption (units/day), smoking (prevalence and cigarettes/day), and alcohol consumption (AUDIT-C score). We divided the nurses into four groups: (1) day workers, (2) night workers, (3) nurses who changed toward, and (4) nurses who changed away from a schedule containing night shifts. Furthermore, average number of yearly night shifts (NN), and average number of quick returns (QR) were calculated. Paired t-tests, McNemar tests, and logistic regression analyses were used in the analyses.

Results: We found a significant increase in caffeine consumption across all work schedule groups and a decline in smoking prevalence for day workers and night workers at follow-up. Analyses did not show any significant differences between groups when analyzing (1) different work schedules, (2) different exposures to QR, (3) different exposures to NN on the respective lifestyle factor trajectories.

Conclusion: We found no significant differences between the different work schedule groups or concerning different exposures to QR or NN when evaluating these lifestyle factor trajectories. This challenges the notion that shift work has an adverse impact on lifestyle factors.

Working against the biological clock: a review for the Occupational Physician

The master clock of the biological rhythm, located in the suprachiasmatic nucleus of the anterior hypothalamus, synchronizes the molecular biological clock found in every cell of most peripheral tissues. The human circadian rhythm is largely based on the light-dark cycle. In night shift workers, alteration of the cycle and inversion of the sleep-wake rhythm can result in disruption of the biological clock and induce adverse health effects. This paper offers an overview of the main physiological mechanisms that regulate the circadian rhythm and of the health risks that are associated with its perturbation in shift and night workers. The Occupational Physician should screen shift and night workers for clinical symptoms related to the perturbation of the biological clock and consider preventive strategies to reduce the associated health risks.

Sleep Assessment During Shift Work in Korean Firefighters: A Cross-Sectional Study

Background

This cross-sectional study assessed the sleep quality using the ActiGraph and investigated the relationship between the parameters of sleep assessment and the type of shift work in Korean firefighters.

Methods

The participants were 359 firefighters: 65 day workers (control group) and 294 shift workers (shift work group: 77 firefighters with 3-day shift, 72 firefighters with 6-day shift, 65 firefighters with 9-day shift, and 80 firefighters with 21-day shift). Sleep assessments were performed using the ActiGraph (wGT3X-BT) for 24 hours during day shift (control and shift work group) and night shift and rest day (shift work group). The participants recorded bed time and sleep hours during the measurement period.

Results

Sleep efficiency, total sleep time, and percentage of wake after sleep onset during night work were lower in the shift work group than control group (p < 0.05). Sleep efficiency decreased in night shift and increased in rest day, whereas wake after sleep onset increased in night shift and decreased in rest day (p < 0.05). Among shift work groups, sleep efficiency of 6-day shift was higher in day shift, and sleep efficiency of 21-day shift was lower in night shift than other shift groups (p < 0.05).

Conclusion

We found that the sleep quality in night shift of the shift work group was poorer than the control group. As to the type of shift work, sleep quality was good in 6-day shift and poor in 21-day shift. Thus, fast rotating shift such as 6-day shift may be recommended to improve the sleep quality of the firefighters.

The effect of shift work on high sensitivity C-reactive protein level among female workers

Background

This study assessed the association between shift work and high-sensitivity C-reactive protein (hs-CRP) level, a risk factor for cardiovascular disease (CVD), in female workers in electronics manufacturing services (EMS).

Methods

Female EMS workers who received special medical examinations for workers in Gyeongnam, Korea between January 2017 and December 2017 were enrolled in this study. Their age, marital status, education level, alcohol consumption, smoking habit, regular exercise, quality of sleep, work stress, and depression were investigated, and blood tests were conducted. The t- and χ² tests were conducted to compare the general and biochemical characteristics between daytime and shift worker groups. Age-adjusted partial correlation analysis was performed to examine the linear relationship between hs-CRP level and other risk factors for CVDs. In addition, the difference in hs-CRP levels according to work schedule was analyzed by ANCOVA after adjusting for variables that could affect the hs-CRP level.

Results

Although the average hs-CRP levels did not differ significantly between daytime and shift workers (0.92 ± 1.87 and 1.07 ± 2.20 mg/dL, respectively), shift workers tended to show a higher hs-CRP level (p = 0.067). After adjusting for variables that can affect the hs-CRP level, the estimated average hs-CRP level was significantly higher in shift workers (1.325 ± 0.156 mg/dL) than that in daytime workers (0.652 ± 0.350 mg/dL) (p = 0.003).

Conclusions

The results of this study identified a relationship between shift work and hs-CRP level increase in women. Because multiple studies have reported associations between increased hs-CRP and CVD, follow-up of hs-CRP may help early detection of CVD in shift workers.

The 5-HTTLPR rs25531 LALA-genotype increases the risk of insomnia symptoms among shift workers

BACKGROUND

Previous studies indicate that shift work tolerance may be associated with individual factors including genetic variability in the gene encoding the serotonin transporter 5-HTT (SLC6A4). The present study aimed to explore the interaction between work schedule (shift work versus non-shift work), genetic variability in SLC6A4 and insomnia symptoms.

METHODS

The study was based on a national probability sample survey of 987 Norwegian employees drawn from The Norwegian Central Employee Register by Statistics Norway. Insomnia symptoms were assessed by three items reflecting problems with sleep onset, sleep maintenance, and early morning awakenings. Genotyping concerning SLC6A4 (the 5-HTTLPR S versus L and the SNP rs25531 A versus G) was carried out using a combination of gel-electrophoresis and TaqMan assay.

RESULTS

Using the L_AL_A genotype as a reference a main effect of the SS genotype (B = 0.179; 95% CI = 0.027-0.330) was found. In addition, a main effect of work schedule (0 = non shift, 1 = shift work) was found (B = 0.504; 95% CI = 0.185-0.823). The genotype x work schedule interaction was significant for all genotypes; SL_A (B = -0.590; 95% CI = -0.954-0.216), L_AL_G (B = -0.879; 95% CI = -1.342-0.415), SL_G (B = -0.705; 95% CI = -1.293-0.117) and SS (B = -0.773; 95% CI = -1.177-0.369) indicating higher insomnia symptom scores among L_AL_A-participants compared to participants with other genotypes when working shifts.

CONCLUSIONS

The ability to cope with shift work is associated with the combination of the SLC6A4 variants 5-HTTLPR and SNP rs25531. Our findings demonstrated that the L_AL_A-genotype increases the risk of insomnia symptoms among shift workers.

Working Time Society consensus statements: Individual differences in shift work tolerance and recommendations for research and practice

There is no standard definition of shift work universally, and no validated report of complete biological adjustment to shift work in workers. Similarly, the evidence for shift work tolerance is limited due to a small number of studies and a narrow range of outcome measures. This paper discusses evidence to date regarding individual differences in shift work tolerance and highlights areas for future research and recommendations for workplace practice. The few factors that are consistently associated with perceived or actual shift work tolerance are young age, low scores of morningness or being a late chronotype, low scores of languidity and neuroticism, high scores on extraversion, internal locus of control and flexibility and male sex. An important first step is to differentiate between factors that are potentially modifiable, such as those that are determined by lifestyle choices, and those factors specific to the working time arrangement. Identifying determinants of shift work tolerance and the ability to adjust to shift work, whether they are innate and/or acquired mechanisms, is important so workers who are less likely to tolerate shift work well can be self-identified and supported with appropriate harm/risk minimization strategies. This paper also identifies important areas for future research with the goal of increasing the evidence base on which we can develop evidence-based harm mitigation strategies for shift workers.

Working hour characteristics and schedules among nurses in three Nordic countries - a comparative study using payroll data

Background

Organisation of working hour schedules in the Northern European countries are rather similar. EU countries are obliged to adopt national legislation regarding duration of weekly working hours and rest periods. Yet, working hour characteristics and schedules are likely to differ with respect to starting times and duration depending e.g. on culture and tradition. Yet, very little is known about potential differences between shifts and schedules across countries among nursing personel. This knowledge is relevant, since the potential differences in working hour characteristics may influence and possibly explain some of the differences observed in studies of health and safety.The aim of the study was to compare characteristics of working hours and work schedules among nursing personel in three Nordic countries: Denmark, Finland and Norway.

Methods

The study populations included nursing personnel holding a ≥ 50% position at public hospitals in Denmark (n = 63,678), Finland (n = 18,257) or Norway (n = 1538) in 2013. Objective payroll based registry data with information on daily starting and ending times were used to compare working hour characteristics e.g. starting time, duration of shift, and quick returns (< 11 h between two shifts), as well as work schedules e.g. permanent or 3-shift work between the three countries.

Results

Night shifts generally started earlier and lasted longer in Finland (10-11 h starting at 20:00-22:59) than in Norway (10 h starting at 21:00-21:59) and in Denmark (8 h starting at 23:00-23:59). Very long shifts (≥12 h) were more common in Denmark (12%) compared to Finland (8%) and Norway (3%). More employees had many (> 13/year) quick returns in Norway (64%) and Finland (47%) compared to Denmark (16%). The frequency of 3-shift rotation workers was highest in Norway (41%) and lower in Denmark (22%) and Finland (22%). There were few differences across the countries in terms of early morning shifts and (very) long weekly working hours.

Conclusion

Despite similar distribution of operational hours among nurses in the three countries, there were differences in working hour characteristics and the use of different types of work schedules. The observed differences may affect health and safety.

The Effect of Special Medical Examination for Night Shift Workers and Follow-Up Management Against Hypertension

Background: Special health examination is a screening program introduced in 1973 in Korea to examine health problems of workers who are regularly exposed to 177 hazardous substances and physical environments specified by the Occupational Safety and Health Act. Shiftwork was added as a risk factor in 2013. The purpose of this study was to analyze changes of hypertension status after a special medical examination and subsequent follow-up management. Methods: We used the data based on the special medical examination outcomes for night shift workers, performed at seven different health examination centers under the Korea Medical Institute (KMI) between 2014 and 2016. Workers who received special medical examinations for two consecutive years (2014–2015 and 2015–2016) were selected. A final study population of 2070 was evaluated. Results: Compared with the first-year examination, 1503 subjects (72.6%) received hypertension medication or showed improvement in blood pressure in their second-year examination. Older age (≥40s), women, larger workplaces (≥300 full-time workers), long-term workers (≥12 years), improvement in smoking habits, improvements for diabetes or dyslipidemia, normal or reduced BMI, and normal waist circumference were associated with proper management of hypertension. Conclusions: An appropriate follow-up management program should be developed to provide health management for night shift workers that need to focus on the factors identified in this study.

Effect of work schedule on prospective antidepressant prescriptions in Sweden: a 2-year sex-stratified analysis using national drug registry data

INTRODUCTION

Depression-related mood disorders affect millions of people worldwide and contribute to substantial morbidity and disability, yet little is known about the effects of work scheduling on depression. This study used a large Swedish survey to prospectively examine the effects of work schedule on registry-based antidepressant prescriptions in females and males over a 2-year period.

METHODS

The study was based on an approximately representative sample (n=3980 males, 4663 females) of gainfully employed participants in the Swedish Longitudinal Occupational Survey of Health. Sex-stratified analyses were conducted using logistic regression. For exposure, eight categories described work schedule in 2008: 'regular days' (three categories of night work history: none, ≤3 years, 4+ years), 'night shift work', 'regular shift work (no nights)', 'rostered work (no nights)', 'flexible/non-regulated hours' and 'other'. For the primary outcome measure, all prescriptions coded N06A according to the Anatomical Therapeutic Chemical System were obtained from the Swedish National Prescribed Drug Register and dichotomised into 'any' or 'no' prescriptions between 2008 and 2010. Estimates were adjusted for potential sociodemographic, health and work confounders, and for prior depressive symptoms.

RESULTS

In 2008, 22% of females versus 19% of males worked outside of regular daytime schedule. Registered antidepressant prescription rates in the postsurvey period were 11.4% for females versus 5.8% for males. In fully adjusted models, females in 'flexible/non-regulated' schedules showed an increased OR for prospective antidepressant prescriptions (OR=2.01, 95% CI=1.08 to 3.76). In males, odds ratios were most increased in those working 'other' schedules (OR=1.72, 95% CI=0.75 to 3.94) and 'Regular days with four or more years' history of night work' (OR=1.54, 95% CI=0.93 to 2.56).

CONCLUSIONS

This study's findings support a relationship between work schedule and prospective antidepressant prescriptions in the Swedish workforce. Future research should continue to assess sex-stratified relationships, using detailed shift work exposure categories and objective registry data where possible.

Cancers in France in 2015 attributable to occupational exposures

BACKGROUND

Recent and comprehensive estimates for the number of new cancer cases in France attributable to occupational exposures are lacking.

OBJECTIVES

To estimate the number of new cancer cases attributable to occupational exposures, using a newly developed methodology and the most recent data, for a comprehensive set of occupational carcinogens in France in 2015.

METHODS

Surveys among employees, the national labor force data, a cohort of agricultural workers, national monitoring of workers exposed to ionizing radiation and job-exposure matrix in France were used. The number and proportion of new cancer cases attributable to established occupational carcinogens (Group 1) was estimated using estimation of lifetime exposure and risk estimates from cohort studies. Cancer data were obtained from the French Cancer Registries Network.

RESULTS

In France in 2015, an estimated 7905 new cancer cases, 7336 among men and 569 among women, were attributable to occupational exposures, representing 2.3% of all new cancer cases (3.9% and 0.4% among men and women respectively). Among men and women, lung cancer was impacted the most, followed by mesothelioma and bladder cancer in men, and by mesothelioma and ovary in women. These cancers contributed to 89% of the total cancers attributable to occupational carcinogens in men, and to 80% in women. The main contributing occupational agent was asbestos among men (45%) and women (60%).

CONCLUSIONS

Currently, occupational exposures contribute to a substantial burden of cancer in France. Enhanced monitoring and implementation of protective labor policies could potentially prevent a large proportion of these cancers.

Migraine, tension-type headache and medication-overuse headache in a large population of shift working nurses: a cross-sectional study in Norway

OBJECTIVES

To investigate associations between different types of headaches and shift work.

DESIGN, PARTICIPANTS AND OUTCOME MEASURES

Nurses with different work schedules (day work, two-shift rotation, night work, three-shift rotation) participated in a cohort study with annual surveys that started in 2008/2009. In 2014 (wave 6), a comprehensive headache instrument was included in the survey, in which 1585 nurses participated. Headaches were assessed according to the International Classification of Headache Disorders IIIb. Frequent headache (≥1 day per month), migraine, tension-type headache, chronic headache (headache >14 days per month) and medication-overuse headache (chronic headache + acute headache medication ≥10 days last month) comprised the dependent variables. Adjusted (for sex, age, percentage of full-time equivalent, marital status, children living at home) logistic regression analyses were conducted with work schedule, number of night shifts worked last year, number of quick returns (<11 hours in-between shifts) last year, shift work disorder and insomnia disorder as predictors.

RESULTS

Frequent headache, migraine and chronic headache were associated with shift work disorder (OR 2.04, 95% CI 1.62 to 2.59; 1.60, 1.21 to 2.12; 2.45, 1.25 to 4.80, respectively) and insomnia disorder (OR 1.79, 95% CI 1.43 to 2.23; 1.55, 1.18 to 2.02; 3.03, 1.54 to 5.95, respectively), but not with work schedule, number of night shifts or number of quick returns. Tension-type headache was only associated with >20 night shifts last year (OR 1.41, 95% CI 1.07 to 1.86). Medication-overuse headache was only associated with insomnia disorder (OR 7.62, 95% CI 2.48 to 23.41).

CONCLUSIONS

We did not find any association between different types of headaches and work schedule. However, tension-type headache was associated with high number of night shifts. Nurses with sleep disorders (insomnia disorder and shift work disorder) reported higher prevalence of frequent headaches, migraine, chronic headache and medication-overuse headache (only insomnia) compared with nurses not having insomnia disorder and shift work disorder, respectively.

Sleep problems in adults with autism spectrum disorder and intellectual disability

Sleep problems (SP) are recognized as a common comorbid condition in autism spectrum disorder (ASD) and can influence core autism symptoms and mental and physical health. SPs can be lifelong and have been reported that adults on the autistic spectrum with and without intellectual disability (ID) present SPs (longer sleep latency, frequent night awakenings, and circadian rhythm sleep-wake disorders). A prospective, objective sleep study was conducted in 41 adults with ASD (33 ± 6 years old) and ID and 51 typically developing adults (33 ± 5 years old) using ambulatory circadian monitoring (ACM) recording wrist temperature, motor activity, body position, sleep, and light intensity. The findings indicated that individuals with ASD presented sleep difficulties including low sleep efficiency, prolonged sleep latency and increased number and length of night awakenings, together with daily sedentary behavior, and increased nocturnal activity. Furthermore, indications of an advanced sleep-wake phase disorder were found in these autistic adults. Examining sleep and markers of the circadian system showed significant differences between adults with ASD and ID and an age-matched, healthy adult population. The sleep disturbances described for this sample of adults with ASD and ID are similar to those of already described for adults with ASD without ID; their relationship with intellectual ability should be further studied. Improving knowledge of sleep patterns in ASD adults with ID might help to designed targeted interventions to improve their functioning and reduce family stress. Autism Research 2019, 12: 66-79. © 2018 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: SPs are very frequent in autism from childhood to adulthood. We recorded sleep with a watch-like device in adults with autism and ID and compared sleep patterns with nonautistic volunteers. Results showed poorer sleep conditions in adults with autism (increased sleep latency and number/length of night awakenings) that resulted in decreased sleep efficiency. Increasing knowledge of the SPs in adults on the autism spectrum will allow to improve their and their families' quality of life.

Who is sleepier on the night shift? The influence of bio-psycho-social factors on subjective sleepiness of female nurses during the night shift

Sleepiness is a common complaint during the night shift and may impair performance. The current study aims to identify bio-psycho-social factors associated with subjective sleepiness during the night shift. Ninety-two female nurses working rotating shifts completed a sociodemographic questionnaire, the Munich ChronoType Questionaire for shift workers, the Pittsburg Sleep Quality Index, and the Pre-sleep Arousal Scale. Subjective sleepiness was measured hourly during two night shifts using the Karolinska Sleepiness Scale, and activity monitors assessed sleep duration 24-h before each shift. Findings showed that increased sleepiness was associated with increased age in nurses with early chronotypes and with more children. High cognitive pre-sleep arousal, but not sleep, was associated with increased sleepiness, especially in late chronotypes. The impact of bio-psycho-social factors on night shift sleepiness is complex, and depends on mutual interactions between these factors. Nurses most prone to increased sleepiness must develop personal strategies for maintaining vigilance on the night shift. Practitioner Summary: This study aims to identify bio-psycho-social factors associated with subjective sleepiness of female nurses during the night shift. Increasing sleepiness was associated with increased age in nurses with early chronotypes and with more children. Increased cognitive pre-sleep arousal, but not sleep, was associated with increased sleepiness, especially in late chronotypes.

Examining Exposure Assessment in Shift Work Research: A Study on Depression Among Nurses

Introduction

Coarse exposure assessment and assignment is a common issue facing epidemiological studies of shift work. Such measures ignore a number of exposure characteristics that may impact on health, increasing the likelihood of biased effect estimates and masked exposure-response relationships. To demonstrate the impacts of exposure assessment precision in shift work research, this study investigated relationships between work schedule and depression in a large survey of Canadian nurses.

Methods

The Canadian 2005 National Survey of the Work and Health of Nurses provided the analytic sample (n = 11450). Relationships between work schedule and depression were assessed using logistic regression models with high, moderate, and low-precision exposure groupings. The high-precision grouping described shift timing and rotation frequency, the moderate-precision grouping described shift timing, and the low-precision grouping described the presence/absence of shift work. Final model estimates were adjusted for the potential confounding effects of demographic and work variables, and bootstrap weights were used to generate sampling variances that accounted for the survey sample design.

Results

The high-precision exposure grouping model showed the strongest relationships between work schedule and depression, with increased odds ratios [ORs] for rapidly rotating (OR = 1.51, 95% confidence interval [CI] = 0.91-2.51) and undefined rotating (OR = 1.67, 95% CI = 0.92-3.02) shift workers, and a decreased OR for depression in slow rotating (OR = 0.79, 95% CI = 0.57-1.08) shift workers. For the low- and moderate-precision exposure grouping models, weak relationships were observed for all work schedule categories (OR range 0.95 to 0.99).

Conclusions

Findings from this study support the need to consider and collect the data required for precise and conceptually driven exposure assessment and assignment in future studies of shift work and health. Further research into the effects of shift rotation frequency on depression is also recommended.

Shift work is associated with reduced heart rate variability among men but not women

BACKGROUND

Imbalance in the autonomic nervous system due to a disrupted circadian rhythm may be a cause of shift work-related cardiovascular diseases.

OBJECTIVE

We aimed to determine the association between shift work and cardiac autonomic activity in blue-collar workers.

METHODS

The study included 665 blue-collar workers aged 18-68 years in different occupations from two Danish cohort studies. Time and frequency domain parameters of heart rate variability (HRV) were measured during sleep using the Actiheart monitor, and used as markers of cardiac autonomic function. Multiple linear regression analyses were used to investigate differences in HRV between day and shift workers.

RESULTS

Shift workers had no significantly different HRV parameters than day workers, except for a lower VLF (B: 0.21; 95% CI: -0.36-0.05). The lower VLF was only present among non-night shift workers (p < 0.05) and not among night shift workers (p > 0.05). Results differed significantly by gender (p for interaction < 0.10): among men, shift work was negatively associated with RMSSD (B: -7.83; 95% CI: -14.28-1.38), SDNN (B: -7.0; 95% CI: -12.27-1.78), VLF (B: -0.27; 95% CI: -0.46-0.09) and Total Power (B: -0.61; 95% CI: -1.20-0.03), while among women, shift work was only associated with the LF/HF ratio (B: -0.29; 95% CI: -0.54-0.03).

CONCLUSION

Shift work was particularly associated with lower HRV during sleep among men. This indicates that shift work causes imbalance in the autonomic nervous system among men, which might increase their risk of cardiovascular diseases.

Restless Legs Syndrome/Willis-Ekbom Disease Is Prevalent in Working Nurses, but Seems Not to Be Associated with Shift Work Schedules

Insomnia and excessive sleepiness are among the most commonly reported sleep problems related to shift work. Sleep-related movement disorders have, however, received far less attention in relation to such work schedules. The objective of this study was to investigate the association between different shift work schedules and the prevalence of Restless legs syndrome/Willis–Ekbom disease (RLS/WED) in a large sample of Norwegian nurses. Our hypothesis was that shift working nurses would report higher prevalence of RLS/WED compared to day workers. A total of 1,788 nurses with different work schedules (day work, two-shift rotation, night work, three shift rotation) participated in a cohort study, started in 2008/2009. Four questions about RLS/WED based on the diagnostic criteria were included in wave 4 (2012). RLS/WED prevalence rates across different shift schedules were explored by the Pearson chi-square test. Logistic regression analysis was used to assess the association between RLS/WED and work schedules and shift work disorder (SWD) with adjustment for sex, age, marital status, smoking, and caffeine use. In total, 90.0% of the nurses were females, mean age 36.5 years (SD = 8.6, range 25–67). The overall prevalence of RLS/WED was 26.8%. We found no significant differences between the prevalence of RLS/WED across the different shift schedules, ranging from 23.3% (day work) to 29.4% (night work). There was a significant difference (p < 0.001) in the prevalence of RLS/WED between nurses having SWD (33.5%) compared to nurses not having SWD (23.8%). SWD remained significantly associated with RLS/WED in the adjusted logistic regression analysis (1.56, CI: 1.24–1.97). This study did not support the hypothesis. RLS/WED was associated with SWD, which might indicate that nurses vulnerable to shift work also are sensitive to other complaints related to a misalignment of the biological clock.

Prevalence of Hypertension in Professional Drivers (from the RACER-ABPM Study)

Professional drivers are a group exposed to many cardiovascular risk factors. Nonsystematic working hours, stress, low physical activity, and unhealthy dietary habits are common among professional drivers. These translate into high risk of cardiovascular disease. The aim of the current analysis was to establish the prevalence of arterial hypertension in a group of continuous professional drivers. The RACER (Risk of Adverse Cardiovascular Events among professional dRivers in Poland) study is a prospective study focused on assessing cardiovascular risk factors in professional drivers. Patients included in the study were screened for the classical and nonclassical cardiovascular risk factors and had an ambulatory blood pressure monitoring (ABPM) performed. Of the RACER study population, 144 drivers were included into the RACER-ABPM study. Of this group 135 (95.7%) were male at mean age of 50.2 ± 9.3 years, with mean body mass index of 32.3 ± 3.0 kg/m². In 21.3% of patients, family history of cardiovascular disease was noted, 28.1% were current smokers, and 2.9% had diabetes mellitus. Arterial hypertension was previously diagnosed in 39 patients (27.9%). In ABPM, the mean 24-hour blood pressure (BP) values were 130.3 ± 14.3 and 80.9 ± 9.9 for systolic and diastolic BP, respectively, and 46.1% of patients could be categorized as dippers. Based on the ABPM results, arterial hypertension was diagnosed in 104 of patients (73.8%). Patients with hypertension tend to be more often male and have a family history of cardiovascular disease. In conclusion, arterial hypertension is highly prevalent in professional drivers. Also abnormal day-to-night BP value patterns are often seen in this group.