The circadian system regulates physiology and behavior. Acute challenges to the system, such as those experienced when traveling across time zones, will eventually result in re‐synchronization to ...local environmental time cues, but this re‐synchronization is oftentimes accompanied by adverse short‐term consequences. When such challenges are experienced chronically, adaptation may not be achieved, as for example in the case of rotating night shift workers. The transient and chronic disturbance of the circadian system is most frequently referred to as “circadian disruption”, but many other terms have been proposed and used to refer to similar situations. It is now beyond doubt that the circadian system contributes to health and disease, emphasizing the need for clear terminology when describing challenges to the circadian system and their consequences. The goal of this review is to provide an overview of the terms used to describe disruption of the circadian system, discuss proposed quantifications of disruption in experimental and observational settings with a focus on human research, and highlight limitations and challenges of currently available tools. For circadian research to advance as a translational science, clear, operationalizable, and scalable quantifications of circadian disruption are key, as they will enable improved assessment and reproducibility of results, ideally ranging from mechanistic settings, including animal research, to large‐scale randomized clinical trials.
This study explores chronotype-dependent tolerance to the demands of working morning, evening, and night shifts in terms of social jet lag, sleep duration, and sleep disturbance. A total of 238 ...shift-workers were chronotyped with the Munich ChronoType Questionnaire for shift-workers (MCTQShift), which collects information about shift-dependent sleep duration and sleep timing. Additionally, 94 shift-workers also completed those items of the Sleep Questionnaire from the Standard Shift-Work Index (SSI) that assess sleep disturbances. Although all participants worked morning, evening, and night shifts, subsamples differed in rotation direction and speed. Sleep duration, social jet lag, and sleep disturbance were all significantly modulated by the interaction of chronotype and shift (mixed-model ANOVAs). Earlier chronotypes showed shortened sleep duration during night shifts, high social jet lag, as well as higher levels of sleep disturbance. A similar pattern was observed for later chronotypes during early shifts. Age itself only influenced sleep duration and quality per se, without showing interactions with shifts. We found that workers slept longer in fast, rotating shift schedules. Since chronotype changes with age, investigations on sleep behavior and circadian misalignment in shift-workers have to consider chronotype to fully understand interindividual and intraindividual variability, especially in view of the current demographic changes. Given the impact of sleep on health, our results stress the importance of chronotype both in understanding the effects of shift-work on sleep and in devising solutions to reduce shift-work–related health problems.
Shift-work seriously affects the health and well-being of millions of people worldwide, and the number of shift workers is constantly rising (currently approximately 20% of the workforce). While some ...effects are acute, others lead to chronic syndromes that persist after retirement. Though health problems in shift workers are well established, we still do not properly understand the causal mechanisms underlying shift-work’s effects on health. One reason may be the heterogeneity in shift-work research design and methodology, rendering comparison between studies difficult or even impossible. Shift-work also involves a multitude of interacting factors, and we do not yet fully understand many of these interactions. Interindividual differences between workers are central predictors for health. Among these, individual differences in internal time (chronotype) should play a key role in a worker’s ability to adjust to shift-work. While the importance of chronotype is receiving increased attention in chronobiology, it is still being largely ignored by shift-work studies, particularly by those performed in the field. Shift-work research would greatly benefit from increased attention to circadian components in real-life shift-work situations. Here, we summarize the current state of shift-work research in an attempt to address the reasons as to why we still do not clearly understand the links between shift-work and health. The aim of shift-work research should ultimately be to improve health and well-being (including social issues) in shift workers by means of improved work schedules. Society as a whole would benefit from such improvements — the individual worker, the health system, and industry.
Sleep loss and circadian disruption—a state of misalignment between physiological functions and imposed sleep/wake behavior—supposedly play central roles in the etiology of shift work-related ...pathologies 1–4. Circadian entrainment is, however, highly individual 5, resulting in different chronotypes 6, 7. Chronotype in turn modulates the effects of working times: compared to late chronotypes, earlier ones sleep worse and shorter and show higher levels of circadian misalignment during night shifts, while late types experience more sleep and circadian disruption than early types when working morning shifts 8. To promote sleep and reduce the mismatch between circadian and working time, we implemented a chronotype-adjusted (CTA) shift schedule in a factory. We abolished the most strenuous shifts for extreme chronotypes (i.e., mornings for late chronotypes, nights for early ones) and examined whether sleep duration and quality, social jetlag 9, 10, wellbeing, subjective stress perception, and satisfaction with leisure time improved in this schedule. Intermediate chronotypes (quartiles 2 and 3) served as a control group, still working morning (6:00–14:00), evening (14:00–22:00), and night (22:00–6:00) shifts, with two strenuous shifts (out of twelve per month) replaced by evening ones. We observed a significant increase of self-reported sleep duration and quality, along with increased wellbeing ratings on workdays among extreme chronotypes. The CTA schedule reduced overall social jetlag by 1 hr, did not alter stress levels, and increased satisfaction with leisure time (early types only). Chronotype-based schedules thus can reduce circadian disruption and improve sleep; potential long-term effects on health and economic indicators need to be elucidated in future studies.
•Extreme chronotypes slept up to 0.5 hr longer on workdays•Self-reported sleep quality in extreme chronotypes improved on workdays•Overall social jetlag was reduced by ≈1 hr•Frequent night shifts are better tolerated by very late chronotypes
The health deficits associated with shift work have been linked to circadian stress and disrupted sleep. Vetter et al. performed the first intervention study in a real-life industrial setting that adjusted shifts to individual chronotype and show that workers sleep longer and better and suffer from less social jetlag.
Social Jetlag and Obesity Roenneberg, Till; Allebrandt, Karla V.; Merrow, Martha ...
Current biology,
05/2012, Letnik:
22, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Obesity has reached crisis proportions in industrialized societies 1. Many factors converge to yield increased body mass index (BMI). Among these is sleep duration 2–10. The circadian clock controls ...sleep timing through the process of entrainment. Chronotype describes individual differences in sleep timing, and it is determined by genetic background, age, sex, and environment (e.g., light exposure) 11–14. Social jetlag quantifies the discrepancy that often arises between circadian and social clocks, which results in chronic sleep loss 11, 15. The circadian clock also regulates energy homeostasis 16, and its disruption—as with social jetlag—may contribute to weight-related pathologies 17–19. Here, we report the results from a large-scale epidemiological study, showing that, beyond sleep duration, social jetlag is associated with increased BMI. Our results demonstrate that living “against the clock” may be a factor contributing to the epidemic of obesity. This is of key importance in pending discussions on the implementation of Daylight Saving Time and on work or school times, which all contribute to the amount of social jetlag accrued by an individual. Our data suggest that improving the correspondence between biological and social clocks will contribute to the management of obesity.
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► In 70% of the population, biological and social clocks differ by >1 hr (social jetlag) ► Social jetlag is a predictor of BMI, especially for overweight individuals ► The decrease of sleep duration over the past decade concerns only workdays ► Individuals are progressively exposed to decreasing light, and their chronotypes delay
Prospective studies linking shift work to coronary heart disease (CHD) have been inconsistent and limited by short follow-up.
To determine whether rotating night shift work is associated with CHD ...risk.
Prospective cohort study of 189,158 initially healthy women followed up over 24 years in the Nurses' Health Studies (NHS 1988-2012: N = 73,623 and NHS2 1989-2013: N = 115,535).
Lifetime history of rotating night shift work (≥3 night shifts per month in addition to day and evening shifts) at baseline (updated every 2 to 4 years in the NHS2).
Incident CHD; ie, nonfatal myocardial infarction, CHD death, angiogram-confirmed angina pectoris, coronary artery bypass graft surgery, stents, and angioplasty.
During follow-up, 7303 incident CHD cases occurred in the NHS (mean age at baseline, 54.5 years) and 3519 in the NHS2 (mean age, 34.8 years). In multivariable-adjusted Cox proportional hazards models, increasing years of baseline rotating night shift work was associated with significantly higher CHD risk in both cohorts. In the NHS, the association between duration of shift work and CHD was stronger in the first half of follow-up than in the second half (P=.02 for interaction), suggesting waning risk after cessation of shift work. Longer time since quitting shift work was associated with decreased CHD risk among ever shift workers in the NHS2 (P<.001 for trend). table: see text
Among women who worked as registered nurses, longer duration of rotating night shift work was associated with a statistically significant but small absolute increase in CHD risk. Further research is needed to explore whether the association is related to specific work hours and individual characteristics.
Sleep Duration and Myocardial Infarction Daghlas, Iyas; Dashti, Hassan S.; Lane, Jacqueline ...
Journal of the American College of Cardiology,
09/2019, Letnik:
74, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Observational studies suggest associations between extremes of sleep duration and myocardial infarction (MI), but the causal contribution of sleep to MI and its potential to mitigate genetic ...predisposition to coronary disease is unclear.
This study sought to investigate associations between sleep duration and incident MI, accounting for joint effects with other sleep traits and genetic risk of coronary artery disease, and to assess causality using Mendelian randomization (MR).
In 461,347 UK Biobank (UKB) participants free of relevant cardiovascular disease, the authors estimated multivariable adjusted hazard ratios (HR) for MI (5,128 incident cases) across habitual self-reported short (<6 h) and long (>9 h) sleep duration, and examined joint effects with sleep disturbance traits and a coronary artery disease genetic risk score. The authors conducted 2-sample MR for short (24 single nucleotide polymorphisms) and continuous (71 single nucleotide polymorphisms) sleep duration with MI (n = 43,676 cases/128,199 controls), and replicated results in UKB (n = 12,111/325,421).
Compared with sleeping 6 to 9 h/night, short sleepers had a 20% higher multivariable-adjusted risk of incident MI (HR: 1.20; 95% confidence interval CI: 1.07 to 1.33), and long sleepers had a 34% higher risk (HR: 1.34; 95% CI: 1.13 to 1.58); associations were independent of other sleep traits. Healthy sleep duration mitigated MI risk even among individuals with high genetic liability (HR: 0.82; 95% CI: 0.68 to 0.998). MR was consistent with a causal effect of short sleep duration on MI in CARDIoGRAMplusC4D (Coronary ARtery DIsease Genome wide Replication and Meta-analysis plus Coronary Artery Disease Genetics Consortium) (HR: 1.19; 95% CI: 1.09 to 1.29) and UKB (HR: 1.21; 95% CI: 1.08 to 1.37).
Prospective observational and MR analyses support short sleep duration as a potentially causal risk factor for MI. Investigation of sleep extension to prevent MI may be warranted.
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Morning diurnal preference is associated with reduced risk of major depressive disorder (MDD); however, causality in this association is uncertain.
To examine the association of genetically proxied ...morning diurnal preference with depression risk using mendelian randomization.
This 2-sample mendelian randomization study used summary-level genetic associations with diurnal preference and MDD. Up to 340 genetic loci associated with diurnal preference in a meta-analysis of the UK Biobank and 23andMe cohorts were considered as genetic proxies for diurnal preference. The effect size of these variants was scaled using genetic associations with accelerometer-based measurement of sleep midpoint. Genetic associations with MDD were obtained from a meta-analysis of genome-wide association studies data from the Psychiatric Genomics Consortium and UK Biobank. The inverse-variance weighted method was used to estimate the association of genetically proxied morning diurnal preference, corresponding to a 1-hour earlier sleep midpoint, with MDD risk.
Morning diurnal preference scaled to a 1-hour earlier, objectively measured sleep midpoint.
Risk of MDD, including self-reported and clinically diagnosed cases, as ascertained in meta-analyses of genome-wide association studies.
A total of 697 828 individuals (all of European ancestry) were in the UK Biobank and 23andMe cohorts; 85 502 in the UK Biobank had measurements of the sleep midpoint. A further 170 756 individuals with MDD and 329 443 control participants (all of European ancestry) were in the Psychiatric Genomics Consortium and UK Biobank data. Genetically proxied earlier diurnal preference was associated with a 23% lower risk of depression (odds ratio OR per 1-hour earlier sleep midpoint, 0.77 95% CI, 0.63-0.94; P = .01). This association was similar when restricting analysis to individuals with MDD as stringently defined by the Psychiatric Genomics Consortium (OR, 0.73 95% CI, 0.54-1.00; P = .05) but not statistically significant when defined by hospital-based billing codes in the UK Biobank (OR, 0.64 95% CI, 0.39-1.06; P = .08). Sensitivity analyses examining potential bias due to pleiotropy or reverse causality showed similar findings (eg, intercept SE, 0.00 0.001; P = .66 by Egger intercept test).
The results of this mendelian randomization study support a protective association of earlier diurnal preference with risk of MDD and provide estimates contextualized to an objective sleep timing measure. Further investigation in the form of randomized clinical trials may be warranted.
Sleep is systematically modulated by chronotype in day-workers. Therefore, investigations into how shift-work affects sleep, health, and cognition may provide more reliable insights if they consider ...individual circadian time (chronotype). The Munich ChronoType Questionnaire (MCTQ) is a useful tool for determining chronotype. It assesses chronotype based on sleep behavior, specifically on the local time of mid-sleep on free days corrected for sleep debt accumulated over the workweek (MSFsc). Because the original MCTQ addresses people working standard hours, we developed an extended version that accommodates shift-work (MCTQShift). We first present the validation of this new version with daily sleep logs (n = 52) and actimetry (n = 27). Next, we evaluated 371 MCTQShift entries of shift-workers (rotating through 8-h shifts starting at 0600 h, 1400 h, and 2200 h). Our results support experimental findings showing that sleep is difficult to initiate and to maintain under the constraints of shift-work. Sleep times are remarkably stable on free days (on average between midnight and 0900 h), so that chronotype of shift-workers can be assessed by means of MSF—similar to that of day-workers. Sleep times on free-days are, however, slightly influenced by the preceding shift (displacements <1 h), which are smallest after evening shifts. We therefore chose this shift-specific mid-sleep time (MSFE) to assess chronotype in shift-workers. The distribution of MSFE in our sample is identical to that of MSF in day-workers. We propose conversion algorithms for chronotyping shift-workers whose schedules do not include free days after evening shifts.
To examine the effects of past and current night shift work and genetic type 2 diabetes vulnerability on type 2 diabetes odds.
In the UK Biobank, we examined associations of current (
= 272,214) and ...lifetime (
= 70,480) night shift work exposure with type 2 diabetes risk (6,770 and 1,191 prevalent cases, respectively). For 180,704 and 44,141 unrelated participants of European ancestry (4,002 and 726 cases, respectively) with genetic data, we assessed whether shift work exposure modified the relationship between a genetic risk score (comprising 110 single-nucleotide polymorphisms) for type 2 diabetes and prevalent diabetes.
Compared with day workers, all current night shift workers were at higher multivariable-adjusted odds for type 2 diabetes (none or rare night shifts: odds ratio OR 1.15 95% CI 1.05-1.26; some nights: OR 1.18 95% CI 1.05-1.32; and usual nights: OR 1.44 95% CI 1.19-1.73), except current permanent night shift workers (OR 1.09 95% CI 0.93-1.27). Considering a person's lifetime work schedule and compared with never shift workers, working more night shifts per month was associated with higher type 2 diabetes odds (<3/month: OR 1.24 95% CI 0.90-1.68; 3-8/month: OR 1.11 95% CI 0.90-1.37; and >8/month: OR 1.36 95% CI 1.14-1.62;
= 0.001). The association between genetic type 2 diabetes predisposition and type 2 diabetes odds was not modified by shift work exposure.
Our findings show that night shift work, especially rotating shift work including night shifts, is associated with higher type 2 diabetes odds and that the number of night shifts worked per month appears most relevant for type 2 diabetes odds. Also, shift work exposure does not modify genetic risk for type 2 diabetes, a novel finding that warrants replication.
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