IntroductionInsomnia in shift workers has distinctive features due to circadian rhythm disruption caused by reversed or unstable sleep-wake cycle work schedules. While previous studies have primarily focused on a limited number of predictors for insomnia severity in shift workers, there is a need to further explore key predictors, and develop a data-driven prediction model for insomnia in shift workers. This study aims to identify potential predictors of insomnia severity in shift workers using a machine learning (ML) approach and evaluate the accuracy of the resulting prediction model.MethodsWe assessed the predictors of insomnia severity in large samples of individuals (4,572 shift workers and 2,093 non-shift workers). The general linear model with the least absolute shrinkage and selection operator (LASSO) was used to determine an ML-based prediction model. Additional analyses were conducted to assess the interaction effects depending on the shift work schedule.ResultsThe ML algorithms identified 41 key predictors from 281 variables: 1 demographic, 7 physical health, 13 job characteristics, and 20 mental health factors. Compared to the non-shift workers, the shift workers showed a stronger association between insomnia severity and five predicting variables: passiveness at work, authoritarian work atmosphere, easiness to wake up, family and interpersonal stress, and medication. The prediction model demonstrated good performance with high accuracy and specificity overall despite a limited F1 score (classification effectiveness) and recall (sensitivity). Specifically, a prediction model for shift workers showed better balance in F1 scores and recall compared to that for non-shift workers.DiscussionThis ML algorithm provides an effective method for identifying key factors that predict insomnia severity in shift workers. Our findings align with the traditional insomnia model while also reflecting the distinctive features of shift work such as workplace conditions. Although the potential for immediate clinical application is limited, this study can serve as guidance for future research in improving a prediction model for shift workers. Constructing comprehensive ML-based prediction models that include our key predictors could be a crucial approach for clinical purposes.

ObjectWe explored the circadian preferences of non-shift workers (non-SWs) and various types of shift workers (SWs), and the associations of these preferences with sleep and mood.MethodsIn total, 4,561 SWs (2,419 women and 2,142 men aged 37.00 ± 9.80 years) and 2,093 non-SWs (1,094 women and 999 men aged 37.80 ± 9.73 years) completed an online survey. Of all SWs, 2,415 (1,079 women and 1,336 men aged 37.77 ± 9.96 years) reported regularly rotating or fixed schedules (“regular SWs”), and 2,146 (1,340 women and 806 men aged 36.12 ± 9.64 years) had irregular schedules (“irregular SWs”). Of the regular SWs, 2,040 had regularly rotating schedules, 212 had fixed evening schedules, and 163 had fixed night schedules. All participants completed the Morningness-Eveningness Questionnaire (MEQ) exploring circadian preferences, the short form of the Center for Epidemiological Studies-Depression Scale (CES-D) evaluating depression, the Insomnia Severity Index (ISI), and the Epworth Sleepiness Scale (ESS).ResultsCompared to non-SWs, SWs had lower MEQ scores, i.e., more eveningness, after controlling for age, gender, income, occupation, and weekly work hours (F = 87.97, p < 0.001). Irregular SWs had lower MEQ scores than regular SWs (F = 50.89, p < 0.001). Among regular SWs, the MEQ scores of fixed evening and fixed night SWs were lower than those of regularly rotating SWs (F = 22.42, p < 0.001). An association between the MEQ and ESS scores was apparent in non-SWs (r = −0.85, p < 0.001) but not in SWs (r = 0.001, p = 0.92).ConclusionSWs exhibited more eveningness than non-SWs; eveningness was particularly prominent in SWs with irregular or fixed evening/night shifts. Eveningness was associated with sleepiness only in non-SWs, but not in SWs.

Background: Social Zeitgeber Theory posits that disruptions in social rhythms can increase susceptibility to bipolar disorder (BD). Shift work (SW) is one of the external factors that cause instability in social rhythms and the sleep -wake cycle. This study evaluated the moderating influences of SW on the risks of BD and sleep -related parameters and depressive symptoms. Furthermore, we evaluated the specific work schedules including daytime, nighttime, and regular and irregular rotating SW. Methods: An online survey was administered to 6665 participants, with 3379 (50.7 %) classified as individuals with high scores of Mood Disorder Questionnaire (MDQ). The survey included the Pittsburgh Sleep Quality Index (PSQI), Insomnia Severity Scale (ISI), Epworth Sleepiness Scale (ESS), and Center for Epidemiologic Studies Depression Scale (CES-D). Results: A multivariate regression model revealed significant interactive effects of MDQ positivity and SW on PSQI, ISI, and CES-D scores, but not ESS scores. In a secondary analysis of the high MDQ screen group, daytime workers had lower scores in sleep disturbances and depressive symptoms compared to those engaged in other forms of SW. Limitations: Online surveys were accessible voluntarily, leading to potential selection bias. Cross-sectional data identified associations, not causal relationships. Only a self -reported questionnaire was used. Conclusions: Our findings emphasize the advantages of a daytime work schedule for individuals at high risk of BD. In accordance with the principles of social rhythm interpersonal therapy, sleep interventions for individuals at high risk of BD should include the maintenance of a consistent daytime schedule.

Objective We investigated the difference in sleep inertia between shift workers (SWs) and non-shift workers (NSWs) and the effects of depressive symptoms, sleepiness, insomnia, and chronotype on sleep inertia in SWs and NSWs. Methods Altogether, 4,561 SWs (2,142 men and 2,419 women, aged 36.99 +/- 9.84 years) and 2,093 NSWs (999 men and 1,094 women, aged 37.80 +/- 9.73 years) participated in the current study. All participants completed the Sleep Inertia Questionnaire (SIQ), EpidemiologQuestionnaire (MEQ) through an online survey. Results SWs reported higher SIQ scores than NSWs after controlling for CESD, ESS, ISI, or MEQ. The CESD, ESS, ISI, and MEQ predicted SIQ in both SWs and NSWs. The effects of CESD and MEQ on SIQ were stronger in SWs and NSWs, respectively. The indirect effects of CESD and MEQ on SIQ via ESS were significantly moderated by work schedules. Conclusion SWs showed higher sleep inertia than NSWs. The effect of chronotypes on sleep inertia was more prominent in NSWs than in SWs. However, the effect of depressive symptoms on sleep inertia was more prominent in SWs than in NSWs. Moreover, the effect of depressive symptoms or chronotypes on sleep inertia was mediated by sleepiness, and such indirect effects were significantly different among the participants stratified by work schedules. Psychiatry Investig

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 (CES-D), 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.

OBJECTIVE:This study investigated whether sleep and stress mutually interact to induce changes in white matter integrity.METHODS:Diffusion tensor imaging (DTI) was conducted on 36 participants (male=22, female=14; mean age=38.33±12.78 years). Participants were divided into three groups depending on their sleep quality and stress levels: poor sleepers with stress, poor sleepers without stress, and good sleepers. Sleep quality and stress level were evaluated using the Pittsburgh Sleep Quality Index and the Life Experiences Survey, respectively. Fractional anisotropy (FA) values were calculated employing DTI tractography.RESULTS:After controlling for age and sex, poor sleepers with stress exhibited a lower FA of the left inferior cerebellar peduncle (ICP) than did poor sleepers without stress (t=2.81, p=0.02). Poor sleepers without stress showed a higher FA of the right middle longitudinal fasciculus (MdLF) than did good sleepers (t=3.35, p=0.006).CONCLUSION:The current study reports the effects of sleep, stress, and their interaction on the white matter integrities of the ICP and MdLF. ICP change seems to be associated with sleep disturbances related to stress, while MdLF change would be associated with sleep disturbances unrelated to stress.

Objective The current study aimed to investigate the differences in sleep reactivity and sleep effort differs among late night shift workers (LSWs) and non-late night shift workers (non-LSWs), and non-shift workers (non-SWs).Methods In total, 6,023 participants (1,613 non-SWs, 3,339 LSWs, and 1,071 non-LSWs) were recruited. Non-SWs was defined as those who works at fixed schedules during standard daylight. LSWs was defined as who work late night hours (10 PM-6 AM), while non-LSWs was SWs who did not work during late night. All completed the Ford Insomnia Response to Stress Test (FIRST), the Glasgow Sleep Effort Scale (GSES), the Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleepiness Scale (ESS), the Insomnia Severity Index (ISI), and the short-term Center for Epidemiologic Studies-Depression scale (CES-D) through online survey.Results LSWs and non-LSWs reported higher FIRST, GSES scores than non-SWs. In addition, LSWs reported higher FIRST, GSES scores than non-LSWs. FIRST scores were correlated with CES-D, PSQI, ISI, and ESS for LSWs, non-LSWs, and non-SWs alike. GSES scores were also correlated with CES-D, PSQI, ISI, and ESS for LSWs, non-LSWs, and non-SWs alike.Conclusion SWs showed higher sleep reactivity and sleep effort than non-SWs. LSWs had higher sleep reactivity and sleep effort than non-LSWs, and these variables are associated with insomnia, daytime sleepiness, and depressive symptoms. Our findings suggests that late night schedule, may increase sleep reactivity and sleep effort, which are associated with sleep and mood disturbances.

ObjectWe investigated burnout and associated factors in non-shift workers (NSWs), shift workers with regular rotating shifts (RRSWs), and shift workers with irregular or unpredictable rotating shifts (IRSWs).MethodsIn total, 5,125 adult workers (1,966 NSWs, 1,936 RRSWs, and 1,223 IRSWs) participated in an online self-reported survey. Job burnout and three dimensions thereof (exhaustion, cynicism, and professional efficacy) were assessed using the Maslach Burnout Inventory—General Survey (MBI-GS). The Center for Epidemiological Studies Depression Scale (CES-D) (depressive symptoms), Pittsburgh Sleep Quality Index (PSQI) (subjective sleep quality), and Korean Occupational Stress Scale (KOSS) (stressful job environment) were also used.ResultsBoth types of shift workers scored higher in terms of exhaustion, cynicism, and poor professional efficacy on the MBI-GS compared with NSWs after controlling for age and gender. IRSWs exhibited higher scores on the exhaustion and professional efficacy dimensions of the MBI-GS compared with RRSWs. After controlling for the CES-D and PSQI scores, we found no significant difference in cynicism among the groups. After controlling for the KOSS score, we found no significant difference in professional efficacy. All MBI-GS dimensional scores were correlated significantly with the CES-D, PSQI, and KOSS scores in all three groups.ConclusionThe job burnout level of rotating shift workers, especially those with irregular shifts, was higher than that of other workers. Cynicism in shift workers may be largely attributable to poor sleep or depression; the poor efficacy of shift workers may be explained by their stressful work environment.

INTRODUCTION:Shift workers are known to have a higher suicide risk than non-shift workers. Sleep disturbance and impulsivity are also risk factors for suicidality. This study investigated the effects of poor sleep and impulsivity on suicidality in shift and non-shift workers. METHODS:In total, 4572 shift workers (37.0 ± 9.84 years, 2150 males) and 2093 non-shift workers (37.8 ± 9.73 years, 999 males) participated in an online self-report survey. Suicidality was assessed using the Suicidal Behaviors Questionnaire. The Pittsburgh Sleep Quality Index was employed to explore subjective sleep quality, the Insomnia Severity Index to detect insomnia, the Epworth Sleepiness Scale (ESS) to evaluate excessive daytime sleepiness (EDS), the Center for Epidemiological Studies-Depression (CES-D) Scale to assess depressive symptoms, and the Impulsive Behavior Scale (UPPS-P) to explore impulsivity. RESULTS:Shift workers showed poorer sleep quality, and greater impulsivity and suicidality, than non-shift workers. Impulsivity, sleep duration, sleep quality, and insomnia were significantly associated with suicidality, independent of depression. For both shift and non-shift workers, sleep quality moderated the association between impulsivity and suicidality. However, the moderating effects of sleep duration and EDS on the association between impulsivity and suicidality were apparent only in non-shift workers, while a moderating effect of insomnia was observed only in shift workers. CONCLUSION:Shift work, sleep disturbances and impulsivity may exacerbate suicide risk. In addition, the interrelationships among insomnia, EDS, impulsivity, and suicidality may differ between shift and non-shift workers.

This study explored sleep disturbances and depression among various types of shift workers (SWs) and non-SWs, focusing on work schedule diversity. We enrolled 6,654 adults (4,561 SWs, 2,093 non-SWs). Based on self-report questionnaires on work schedules, the participants were classified according to shift work type: non-shift work; and fixed evening, fixed night, regularly rotating, irregularly rotating, casual, and flexible shift work. All completed the Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), Insomnia Severity Index (ISI), and short-term Center for Epidemiologic Studies-Depression scale (CES-D). SWs reported higher PSQI, ESS, ISI, and CES-D than non-SWs. Fixed SWs (fixed evenings and fixed nights) and true SWs (regularly and irregularly rotating SWs) scored higher on the PSQI, ISI, and CES-D than non-SWs. True SWs scored higher on the ESS than fixed SWs and non-SWs. Among fixed SWs, fixed night SWs scored higher on the PSQI and ISI than fixed evening SWs. Among true SWs, irregular SWs (irregularly rotating and casual SWs) scored higher on the PSQI, ISI, and CES-D compared to regularly rotating SWs. The PSQI, ESS, and ISI independently were associated with the CES-D of all SWs. We found an interaction between the ESS and the work schedule on the one hand, and the CES-D on the other, which was stronger in SWs than non-SWs. Fixed night and irregular shifts were linked with sleep disturbances. The depressive symptoms of SWs are associated with sleep problems. The effects of sleepiness on depression were more prominent in SWs than non-SWs.

Purpose:Sounds play important roles in promoting and disrupting sleep. How our brain processes sleep-related sounds and individual differences in processing sleep-related sounds must be determined to understand the role of sound in sleep. We investigated neural responses to sleep-related sounds and their associations with cognitive appraisals of sleep.Participants and Methods:Forty-four healthy adults heard sleep-related and neutral sounds during functional magnetic resonance imaging using a 3T scanner. They also completed the Dysfunctional Beliefs and Attitudes about Sleep (DBAS) questionnaire, which was used to assess cognitive appraisals of sleep. We conducted a voxel-wise whole-brain analysis to compare brain activation in response to sleep-related and neutral sounds. We also examined the association between the DBAS score and brain activity in response to sleep-related sounds (vs neutral sounds) using region of interest (ROI) and whole-brain correlation analyses. The ROIs included the anterior cingulate cortex (ACC), anterior insula (AI), and amygdala.Results:The whole-brain analysis revealed increased activation in the temporal regions and decreased activation in the ACC in response to sleep-related sounds compared to neutral sounds. The ROI and whole-brain correlation analyses showed that higher DBAS scores, indicating a negative appraisal of sleep, were significantly correlated with increased activation of the ACC, right medial prefrontal cortex, and brainstem in response to sleep-related sounds.Conclusion:These results indicate that the temporal cortex and ACC, which are implicated in affective sound processing, may play important roles in the processing of sleep-related sounds. The positive association between the neural responses to sleep-related sounds and DBAS scores suggest that negative and dysfunctional appraisals of sleep may be an important factor in individual differences in the processing of sleep-related sounds.

Introduction:Shift work is known to reduce productivity and safety at work. Previous studies have suggested that a variety of interrelated factors, such as mood, cognition, and sleep, can affect the performance of shift workers. This study aimed to identify potential pathways from depression, sleep, and cognition to work performance in shift and non-shift workers.Material and methods:Online survey including the Center for Epidemiologic Studies Depression Scale (CES-D), Cognitive Failure Questionnaire (CFQ), and Pittsburgh Sleep Quality Index (PSQI), as well as two items representing work mistakes were administered to 4,561 shift workers and 2,093 non-shift workers. A multi-group structural equation model (SEM) was used to explore differences in the paths to work mistakes between shift and non-shift workers.Results:Shift workers had higher PSQI, CES-D, and CFQ scores, and made more mistakes at work than non-shift workers. The SEM revealed that PSQI, CES-D, and CFQ scores were significantly related to mistakes at work, with the CFQ being a mediating variable. There were significant differences in the path coefficients of the PSQI and CES-D between shift and non-shift workers. The direct effects of sleep disturbances on mistakes at work were greater in shift workers, while direct effects of depressive symptoms were found only in non-shift workers.Discussion:The present study found that shift workers made more mistakes at work than non-shift workers, probably because of depressed mood, poor sleep quality, and cognitive inefficiency. Sleep influences work performance in shift workers more directly compared to non-shift workers.

Introduction:We investigated the white matter integrity in shift and non-shift workers and its associations with sleep and activity. Methods:Diffusion tensor imaging (DTI) was performed on 61 shift workers and 31 non-shift workers. Their sleep and activity profiles were assessed using the Pittsburgh Sleep Quality Index (PSQI), sleep diaries, and actigraphy. Fractional anisotropy (FA) (a measure of white matter integrity) was calculated using DTI tractography. Results:Shift workers exhibited higher FA values in the bilateral anterior cingulum than did non-shift workers. An increased FA in the right anterior cingulum was correlated with poor sleep quality (ie, a high PSQI score) in shift workers. An increased FA in the right anterior cingulum was also correlated with higher actigraphic activity indices (the mesor and M10 indices) in shift workers. Discussion:The white matter integrity of the anterior cingulum was altered in shift workers, perhaps in association with sleep and activity disturbances.