Shift Work Disorder Research Articles

Ergonomics in Management of Stress amongst the Night Shift Workers: A Preliminary Review

Working on night shift is basically going against the circadian rhythm. Biological clock inside the human insists to fixed working status on daytime and rest/sleep at night. Ergonomics deals with providing a healthy relation between man machine and environment, where man fits to the job generates ultimate productivity. People in the east who are compromised to adjust in low to middle income are the main sufferers of not having optimum sleep. The population of security services, drivers, loco-pilots, nurses, tele-sales, IT professionals, various millworkers etc. often have shift based jobs and tries to accustom in it by compromising the biological clock. Many research evidences have been showed that alterations in biological clock lead to cause severe insomnia & shift work sleep disorder leading in disturbing occupational health as well as safety. Even sudden alterations in the biological clock lead cause accident, injuries alike from common health distresses. Alteration in the work rest cycle, taking sufficient rest in between the works, getting sufficient scopes in changing postures by arrangements of refreshments in the work place can help in optimizing productivity in the work place. Rotational shift with dynamic posture based work may lower the tendencies of accident and risk associated with night shift based work.

The moderating role of protective factors in shift work disorder and health outcomes: A cross-sectional study

ABSTRACT This study investigated whether sleep-specific (e.g. chronotype) and traditional (e.g. resilience) protective factors were associated with reduced shift work disorder (SWD) risk and explored their role as moderators in the relationship between SWD risk and health. Shift workers (n = 126) participated in a cross-sectional study evaluating SWD risk (i.e. low vs. high; SWD-screening Questionnaire), mental health (Patient Health Questionnaire-9; Generalized Anxiety Disorder Questionnaire-7), physical health (Subjective Health Complaints Inventory), sleep (Pittsburgh Sleep Quality Index; Insomnia Severity Index; Epworth Sleepiness Scale), and protective factors (Resilience Scale; Social Provisions Scale; Survey of Perceived Organizational Support; Short Impulsive Behavior Scale; Circadian Type Inventory; reduced-Morningness-Eveningness Questionnaire). Logistic regressions revealed lower sleep languidity was associated with reduced odds (OR = 0.88 [0.79,0.96]) for having high SWD risk. Multiple regression analyses showed in shift workers with high social support or morningness, having high SWD risk was not associated with increased depression symptoms, or insomnia severity and poor sleep quality, respectively. Finally, in those with high or medium levels of perceived organizational support, high SWD risk was not associated with increased gastrointestinal and allergy complaints. Longitudinal research with larger samples is needed to confirm the moderating role of protective factors in the relationship between SWD risk and health.

Efficacy of Omega-3 in Improving Sleep Quality of Healthcare Workers with Shiftwork Sleep Disorder: Phase III, Double-blind, Placebo-controlled Trial Study Protocol (SLEEP-O3 Trial)

Efficacy of Omega-3 in Improving Sleep Quality of Healthcare Workers with Shiftwork Sleep Disorder: Phase III, Double-blind, Placebo-controlled Trial Study Protocol (SLEEP-O3 Trial)

Efficacy of Omega-3 in Improving Sleep Quality of Healthcare Workers with Shiftwork Sleep Disorder: Phase III, Double-blind, Placebo-controlled Trial Study Protocol (SLEEP-O3 Trial)

Introduction: Healthcare workers are especially vulnerable to sleep disturbances, including shift work sleep disorder (SWSD). Even though omega-3 supplementation has been studied to enhance sleep quality in different populations, there is lack of evidence to support its effectiveness in SWSD. This trial aims to evaluate this compound potential benefits towards health care personnel suffering from SWSD. Methods: This study protocol consists of a phase III, single-center, double-blind, placebo-controlled randomized clinical trial. Participants will receive sleep hygiene orientation in addition to either omega-3 dietary supplementation or placebo for 8 weeks. The primary outcome will be sleep quality as measured by the Pittsburgh Sleep Quality Index and one of the secondary outcomes would be actigraphy as a reliable sleep assessment. The sample size will be 136 subjects. Discussion: The importance of improving sleep quality of health care workers relies on its impact on their wellness, and on patient safety. Sleep deprivation and disorders are responsible for multiple workplace errors and worse health outcomes alike. This trial can help determine if omega-3 supplementation can contribute to ameliorate sleep disturbances in health care professionals.

Sleep Behaviors and Nutritional Knowledge in Amateur and Professional Combat Sport Athletes.

Dunican, IC, Galpin, A, Turner, M, and Reale, R. Sleep behaviors and nutritional knowledge in amateur and professional combat sport athletes. J Strength Cond Res 38(9): 1627-1634, 2024-Combat sports is a term applied to various competitive contact sports involving 2 competitors engaging in a bout or contest under a specific ruleset. Little is known about combat sports athletes' sleep and nutritional knowledge. This study aimed to assess (a) sleep behaviors, (b) alcohol and shiftwork disorders, and (c) the nutritional knowledge of combat sports athletes. Subjects completed various demographic questions and estimations of their weight management practices and validated surveys, including the Athlete Sleep Behavior Questionnaire, Shiftwork Disorder (SWD) Screening Questionnaire, Alcohol Use Disorders Identification Test, and the Abridged Nutrition for Sports Knowledge Questionnaire. A total of 844 combat sports athletes completed the survey, 79% male, height of 177 ± 10 (cm), and body mass of 79 ± 15 (kg). Subjects were categorized into their specific combat sport type (e.g., boxing or Brazilian jiu-jitsu [BJJ]) and by their level (professional or amateur). Sleep quality was average for all combat sport types and risk prevalence of shiftwork disorder at 11%. Mann-Whitney U tests revealed that amateurs, compared with professional strikers ( p = 0.046, CLES = 0.80), boxers ( p = 0.01, CLES = 0.78), and BJJ ( p = 0.046, CLES = 0.61) athletes, consumed significantly more alcohol. A Friedman test showed significant ( p < 0.001, W = 0.51) differences in weight between time points, with most combat sports athletes reducing weight for competition. An overall nutritional knowledge average of 55% was reported. This study highlights a critical gap in the knowledge and practices of combat sports athletes in relation to sleep behaviors and disorders, alcohol consumption, and nutritional knowledge, emphasizing the need for targeted educational interventions.

Unhappy Pictures of Shift Drivers and Proposed Model of Chronoclinic

“Shift work is commonly associated with health problems resulting in circadian misalignment and sleep restriction. Specially shift drivers, are affected by insomnia and up to 90% report regular fatigue and sleepiness at the workplace. According to Ayurveda, Nidra vega dharana/ Ratri jagarana causes Rookshata and Vataprakopa which leads to Vishamata in Doshas and Dhatus. Epidemiological data shows that shift workers are at increased risk of both physical and psychological health problems and shift work disorders (SWSD). These conditions typically lead to reduced work performance, road accidents, absenteeism and reduced quality of life. Given these wide spread and debilitating consequences there is an urgent need for treatment that help to improve the sleep and functional performance of the shift working drivers. The most common non pharmacological recommendations are, well planned shift scheduling, bright light exposure, napping, psychological counselling and education promoting sleep hygiene, and cognitive behavioural techniques. Along with these, implementation of chronoclinics and chronotherapy is very much needed. This article is dealing with deleterious consequences of shift work and some positive ways to optimize shift schedule and some recommendations to improve their health and sleep.

The association between shift work, shift work sleep disorders and premature ejaculation in male workers

ObjectiveShift work and Shift Work Sleep Disorder (SWSD) are known to affect the secretion of several neurotransmitters and hormones associated with premature ejaculation (PE). However, their specific influence on the regulation of male ejaculation remains unclear. This study explores the relationship between shift work, SWSD, and PE.MethodsFrom April to October 2023, a cross-sectional survey was conducted across five regions of China to explore the work schedules, sleep quality, and sexual function of male workers. Participants' sleep quality was evaluated using a validated SWSD questionnaire, and their erectile function and ejaculatory control were assessed with the International Inventory of Erectile Function (IIEF-5) scores and Premature Ejaculation Diagnostic Tool (PEDT) scores, respectively. Univariate and multivariate linear regression analyses were employed to identify risk factors associated with PE. Confounders were controlled using multiple regression models, and clinical prediction models were developed to predict PE onset and assess the contribution of risk factors.ResultsThe study included 1239 eligible participants, comprising 840 non-shift workers and 399 shift workers (148 with SWSD and 251 without SWSD). Compared to non-shift working males, those involved in shift work (β 1.58, 95% CI 0.75 – 2.42, p < 0.001) and those suffering from SWSD (β 2.86, 95% CI 1.86 – 3.85, p < 0.001) they had significantly higher PEDT scores. Additionally, we identified daily sleep of less than six hours, depression, anxiety, diabetes, hyperlipidemia, frequent alcohol consumption (more than twice a week), and erectile dysfunction as risk factors for PE. The predictive model for PE demonstrated commendable efficacy.ConclusionBoth shift work and SWSD significantly increase the risk of premature ejaculation, with the risk magnifying in tandem with the duration of shift work. This study reveals the potential impact of shift work and SWSD on PE and provides new theoretical foundations for the risk assessment and prevention of this condition.

Factors leading to excessive fatigue in nurses – a three-year follow-up study

BackgroundGlobal nursing shortages necessitate the identification of mitigatable factors that may reduce nursing absence and turnover. Fatigue has been shown to be associated with these issues. This study aimed to identify factors leading to development of or recovery from excessive fatigue in nurses as these can offer actionable avenues for protecting nurses against fatigue or supporting fatigue recovery.MethodsA longitudinal study among nurses randomly sampled from the Norwegian Nurse’s Organization. The Chalder Fatigue Questionnaire measured fatigue. Dichotomized scoring was used, with scores ≥ 4 considered excessive fatigue. The study included questions on shift work schedules, psychosocial work characteristics, sleep, body mass index, physical activity, caffeine, alcohol, mental health, etc. Two sets of logistic regression analysis were conducted (one for development of and one for recovery from excessive fatigue), evaluating how changes in work, lifestyle and health between baseline (2015) and follow-up (2018) affected first, odds of development of excessive fatigue and second, odds of recovery from excessive fatigue.ResultsAmong 1,311 included nurses, 21.6% maintained, 13.3% developed, and 18.0% recovered from excessive fatigue (2015–2018). Within work characteristics, increased psychological work demands were associated with development of excessive fatigue OR = 1.77 (CI = 1.11–2.82). Several work characteristics were associated with recovery from excessive fatigue, including decreased decision latitude (OR = 0.39; CI = 0.19–0.82) and increased coworker support (OR = 1.90; CI = 1.11–3.24). Shift work variables were not associated with fatigue outcomes. Amongst lifestyle factors, changes in sleep duration, obesity, and exercise were significant. Notably, developing inappropriate sleep duration (OR = 2.84; CI = 1.47–5.48) increased odds of developing excessive fatigue, while maintaining inappropriate sleep duration (< 6 h or > 8 h) (OR = 0.19; CI = 0.54–0.65) decreased odds of recovering. All assessed health conditions (depression, anxiety, insomnia, and shift work disorder) were related to development of (ORs 2.10–8.07) or recovery from (ORs 0.10–0.50) excessive fatigue. Depression, for example, increased odds of development of (OR = 8.07; CI = 2.35–27.66) and decreased odds of recovery (OR = 0.10; CI = 0.04–0.26) from excessive fatigue.ConclusionsChanges in lifestyle factors, health conditions, and psychosocial work factors were associated with development of and recovery from excessive fatigue. Sleep and psychosocial work factors played important roles. We found no relationship with shift work schedules.

Multifaceted Roles of Melatonin in Sleep Disorders

Hormone protein melatonin helps regulate the sleep–wake cycle or circadian rhythm, making it a critical substance in sleep regulation. Melatonin synthesis mainly occurs in the epiphysis of the pineal gland, although extra-pineal melatonin has been observed in other sites of the body, such as salivary glands, the gastrointestinal tract, the placenta and breast milk. Over the years, research into melatonin has shown that it has multiple roles in sleep disorders, revealing its mechanisms of action, clinical implications and therapeutic performance. In this paper, we review recent findings on the role of melatonin in sleep disorders which include insomnia, delayed sleep phase disorder (DSPD), jet lag, and shift work sleep disorder (SWSD). In addition, we report results where melatonin agonists and novel therapeutic targets have been designed and utilized to manipulate the melatonin receptors. This paper helps delineate melatonin’s role in sleep disorders from the literature, and clarify new perspectives for prevention and treatment of human health.

0351 Protective Factors Buffer the Impact of High Shift Work Disorder Risk on Health Outcomes

0351 Protective Factors Buffer the Impact of High Shift Work Disorder Risk on Health Outcomes

Digital cognitive behavioural therapy for insomnia reduces insomnia in nurses suffering from shift work disorder: A randomised-controlled pilot trial.

Insomnia is a primary symptom of shift work disorder, yet it remains undertreated. This randomised-controlled pilot trial examined the efficacy of a digital, guided cognitive behavioural therapy for insomnia adapted to shift work (SleepCare) in nurses with shift work disorder. The hypothesis was that SleepCare reduces insomnia severity compared with a waitlist control condition. A total of 46 unmedicated nurses suffering from shift work disorder with insomnia (age: 39.7 ± 12.1 years; 80.4% female) were randomised to the SleepCare group or the waitlist control group. The primary outcome measure was the Insomnia Severity Index. Other questionnaires on sleep, mental health and occupational functioning, sleep diary data and actigraphy data were analysed as secondary outcomes. Assessments were conducted before (T0), after the intervention/waitlist period (T1), and 6 months after treatment completion (T2). The SleepCare group showed a significant reduction in insomnia severity from T0 to T1 compared with the control condition (β = -4.73, SE = 1.12, p < 0.001). Significant improvements were observed in sleepiness, dysfunctional beliefs about sleep, pre-sleep arousal, sleep effort, self-reported sleep efficiency and sleep onset latency. No significant effect was found in actigraphy data. Depressive and anxiety symptoms, cognitive irritation and work ability improved significantly. Overall, satisfaction and engagement with the intervention was high. SleepCare improved insomnia severity, sleep, mental health and occupational functioning. This is the first randomised-controlled trial investigating the efficacy of digital cognitive behavioural therapy for insomnia in a population suffering from shift work disorder with insomnia. Future research should further explore these effects with larger sample sizes and active control conditions.

Behavioural therapy for shift work disorder improves shift workers' sleep, sleepiness and mental health: A pilot randomised control trial.

The present study evaluates the efficacy of behavioural therapy adapted for shift work disorder with a randomised control design in a healthcare population. Forty-three night shift workers (m. age: 34 years; 77% women) experiencing shift work disorder were randomised to either the behavioural therapy for shift work disorder (BT-SWD) or a waiting-list control group offered after the waiting period. Participants completed questionnaires on insomnia, sleepiness and mental health pre- and post-treatment, pre- and post-waiting, and at follow-up, and a sleep diary. As night shift workers alternate between sleeping during the day after their night shifts and transitioning to nighttime sleep on days off, insomnia severity and sleep variables were analysed for daytime and nighttime sleep. The BT-SWD involved sleep restriction therapy, stimulus control and fixed sleep periods in the dark. Statistical analyses were performed under intent-to-treat and per-protocol approaches. Repeated-measures two-way ANCOVA analysis, controlling for age, sex and pre-treatment daytime total sleep time, was performed with Bonferroni corrections, and between-group effect sizes computed. Fourteen participants dropped out after randomisation. Under the intent-to-treat analysis, BT-SWD participants had a significant greater decrease in daytime insomnia severity and an increase in daytime total sleep time at post-treatment than the control group, with large between-group effect sizes (-1.25 and 0.89). These corresponding results were also significant with large effect sizes under the per-protocol analysis. Sleepiness, anxiety and depression levels improved at post-treatment and maintained at follow-up when the BT-SWD treated controls were added to the BT-SWD group. The behavioural therapy for shift work disorder can be used to improve the sleep and mental health of healthcare night workers.

Sleep Strategies for Shift Work Nurses

To meet the demands of a 24/7 society, shift work is necessary. Shift work is outside the traditional regular 9-to-5 work schedule, is characterized by irregular working hours, and exists in various industries. However, this abnormal working time can disrupt the natural day and night rhythm, and if poorly adjusted, it can lead to shift work sleep disorder (SWSD). SWSD is associated with multiple health risks, including impaired cognitive function, increased risk of accidents, and various metabolic and cardiovascular diseases. The frontline nurses typically work shifts to provide comprehensive patient care. This article aims to discuss sleep physiology, apply existing literature to discuss the impact on nurses resulting from shift work, and further offer strategies to regulate sleep to promote physical and mental health. These strategies range from organizational interventions (e.g., optimizing shift schedules) to individual interventions (e.g., lifestyle changes) and the use of chronobiological techniques (e.g., light therapy) to promote the adjustment of circadian rhythms, etc.

The long-term effect of work schedule, shift work disorder, insomnia and restless legs syndrome on headache among nurses: A prospective longitudinal cohort study.

The preset study aimed to explore whether work schedules and sleep disorders predict the onset of headache. A longitudinal study was conducted with questionnaire data from 2014 (baseline) and 2017 (follow-up) on work schedule, number of night shifts, number of quick returns, insomnia, shift work disorder (SWD), restless legs syndrome (RLS) and validated headache diagnoses among 1560 Norwegian nurses. Associations were explored by multivariate regression analyses. Work related factors at baseline did not predict onset of headache three years later. In the adjusted logistic regressions, insomnia at baseline predicted increased risk of new onset of migraine (odds ratio (OR) = 1.58; 95% confidence interval (CI) = 1.08-2.33), chronic headache (OR = 2.02; 95% CI = 1.04-4.66) and medication-overuse headache (OR = 3.79; 95% CI = 1.26-11.42) at follow-up. SWD at baseline predicted new onset of migraine (OR = 1.64; 95% CI = 1.07-2.50) and RLS at baseline predicted new onset of headache ≥1 day per month (OR = 1.55; 95% CI = 1.01-2.36) and migraine (OR = 1.55; 95% CI = 1.03-2.32) at follow-up. No factors predicted tension-type headache. Overall, work related factors did not predict the onset of headache three years later, whereas insomnia, SWD and RLS at baseline all increased the risk of future headaches.

Daytime sleepiness in health-care employees: A cross-sectional study between shift duty and day duty

Background: Shift duty disrupts the sleep-wake cycle, leading to shift work disorder, which is characterized by daytime sleepiness and insomnia. Excessive daytime sleepiness decreases work performance, increases workplace accidents, and impairs neurocognitive function. Sleep disturbance also impacts the employee-patient relationship; thereby, it is necessary to assess the prevalence of daytime sleepiness. Aim and Objective: The aim of the study is to compare the prevalence of daytime sleepiness in healthcare employees working in the daytime versus shift duty. Materials and Methods: Subjects were chosen from the Parent Institute between the ages of 24 and 38. A total of 260 health-care employees were included in the study and were divided into two equal groups, with one working on day duty and the other working on shift duty. To evaluate subjective and objective daytime sleepiness, the Epworth sleepiness scale questionnaire was given to both groups. Results: The parameters were analyzed statistically. There was a significant difference in daytime sleepiness between the two groups. There was increased daytime sleepiness in health-care employees working on shift duty as compared to those working on day duty. Conclusion: Sleep deprivation due to disruption of internal sleep regulation leading to shift work disorder is thought to be an important cause of increased daytime sleepiness in health-care employees working on shift duty.

Sleep Disruption, Fatigue, and Altered Neurobehavioral Performance Among Flight Controllers During Spaceflight Operations

In spaceflight operations, flight controllers manage technical aspects of spaceflight control and spacecraft systems. The flight control team is a group subjected to shift work. Acute and chronic exposure to shift work has been associated with circadian misalignment, sleep impairment, and a negative impact on cognitive performance. This study aims to review the effects of shift work on sleep, circadian rhythms, mood, and cognitive performance of flight controllers during real and simulated spaceflight operations. Shift work during low-Earth orbit spaceflight missions is associated with a reduction in alertness, motivation, processing speed, and working memory performance efficiency. Flight controllers also report excessive insomnia and insufficient total sleep time. The development of shift work sleep disorder may be present in up to 40% of workers, especially among night and evening shift workers. Mars operations and Mars-simulated missions are associated with an impairment of visual-motor performance, working memory efficiency, and reaction time. Between 50%–87% of controllers can synchronize their circadian rhythm to a Mars day (24.65 hours), although this adaptation is not reflected in improved neurobehavioral performance.

The relationship of shift work disorder with symptoms of depression, anxiety, and stress

Shift workers commonly suffer from disturbed sleep, which is known to affect mental health in other populations. Shift work disorder (SWD) is characterized by complaints of insomnia and/or excessive daytime sleepiness temporally associated with working non-standard schedules that occur during the usual time for sleep. Few studies have explored the extent to which workers with vs. without SWD experience worse mental health. We administered the Shift Work Disorder Screening Questionnaire to 60 adults engaged in various shift work schedules to categorize workers as being at high or low risk for SWD. Mental health outcomes were measured using the Depression Anxiety Stress Scale-21 (DASS-21). Linear regression was performed for each DASS-21 subscale, adjusting for age, sex, shift type, sleep duration, and frequency of alcohol use. Most participants (55 %) were at high risk for SWD. High-risk participants had higher depressive symptoms than low-risk participants, B = 3.59, 95 % CI [0.54, 6.65], p = .02. The estimated value for those at high risk for SWD corresponded to clinically significant mild depressive symptoms, (M = 13.43), compared to those at low risk, (M = 9.84). High risk for SWD was marginally associated with increased stress symptoms, B = 2.48, 95 % CI [-0.06, 5.02], p = .06. Our findings add to the body of evidence that SWD is associated with poor mental health outcomes. Providing interventions specific to the sleep impacts of SWD, including tailored cognitive behavioral therapy for insomnia, may improve shift workers’ mental health.

Bibliometric and Visualized Analysis of Shift Work Sleep Disorders from 2003 to 2023

Bibliometric and Visualized Analysis of Shift Work Sleep Disorders from 2003 to 2023

Differences in shift and work-related patterns between metropolitan and regional/rural healthcare shift workers and the occupational health and safety risks.

To explore if there are differences in shift patterns and work-related factors between metropolitan and regional/rural healthcare shift workers and their risk of poor sleep and mental health. Furthermore, explore whether these factors impact on medical errors, workplace and car/near car accidents. A cross-sectional study. An anonymous online survey of healthcare shift workers in Australia. A total of 403 nurses, midwives and paramedics completed the survey. Sample characteristics, employment location, shift work-related features, sleep and mental health measurements, workplace accidents, medical errors and car/near car accident post shift. Regional/rural healthcare shift workers were significantly older, had more years' experience, worked more nights, on-call and hours per week. Those in metropolitan areas took significantly longer (minutes) to travel to work, had higher levels of anxiety, increased risk of shift work disorder, reported significantly more workplace accidents and were more likely to have a car/near car accident when commuting home post shift. Both groups reported ~25% having a medical error in the past year. Workplace accidents were related to more on-call shifts and poor sleep quality. Medical errors were associated with fewer years' experience, more evening shifts and increased stress. Car accidents were associated with metropolitan location and increased depression. Differences in work-related factors between metropolitan and regional/rural healthcare shift workers were observed. Some of these factors contributed to occupational health and safety risks. Further exploration is needed to understand how to reduce occupational health and safety risks, and improve employee and patient safety both in both regional/rural and metropolitan areas.

Shift work is associated with extensively disordered sleep, especially when working nights.

Shift work is generally associated with working and sleeping out of phase with the endogenous, circadian sleep-wake cycle. This exerts detrimental effects on sleep health. The present study aimed at evaluating the presence of short and long sleep as well as sleep disorders within a broad range of shift work schedules and elucidating the role of sociodemographic factors therein. A large dataset containing information on sleep was collected through advertisement in a Belgium newspaper (De Standaard). Adult, working individuals were selected (n = 37,662) and categorized based on their work schedule (regular day, early morning, evening, night, and rotating shift). In this cross-sectional study, prevalence rates of short sleep (≤6 h), long sleep (≥9 h) and sleep disorders (screened with Holland Sleep Disorders Questionnaire), and associations between these sleep variables and sociodemographics (age, sex, education, living companion(s)) were analyzed using binominal logistic regression analyses. In the total sample all sociodemographic factors affected prevalences of short, long and disordered sleep, consistent with previous studies. Compared to day workers, shift workers more frequently reported short sleep, most prominently night workers (26 vs. 50%) (p < 0.001). Furthermore, all sleep disorders as well as sleep disorder comorbidity were more common in shift workers, again most pronounced in night workers (all p < 0.05). In night shift workers the level of education had the strongest associations with disturbed sleep with a two-fold higher prevalence of short and disordered sleep in low relative to academic educated groups (all p < 0.02). Shift work is related not only to curtailed sleep and shift work disorder, but also to a plethora of sleep disorders, including insomnia, sleep-related breathing disorders and sleep-related movement disorders. Our findings imply that education on coping strategies may be especially important for young and/or lower educated shift workers.