Night shift work, long working hours and dementia: a longitudinal study of the Danish Work Environment Cohort Study

Shift work effects on incident neuropsychiatric disorders and shift work tolerance

BACKGROUND

Shift work is associated with susceptibility to several neuropsychiatric disorders. This study aims to investigate the effect of shift work on the incidence of neuropsychiatric disorders, and highlighting how individual variability may influence the association.

METHODS

UK Biobank participants with employment information were included. Cox survival was conducted in main and subgroup analyses. Correlation analyses explored the impact of shift work on brain structures, and mediation analyses were performed to elucidate the shared underlying mechanisms. Shift work tolerance was evaluated through survival analyses contrasting the risks associated with five neuropsychiatric disorders in shift versus non-shift workers across different demographic or occupational strata.

RESULTS

The analysis encompassed 254,646 participants. Shift work was associated with higher risk of dementia (HR 1.29, 95 % CI 1.10-1.52), anxiety (1.08, 1.01-1.15), depression (1.29, 1.22-1.36), and sleep disorders (1.18, 1.09-1.28), but not stroke (p = 0.20). Shift work was correlated with decreasing volume of various brain regions, particularly in thalamus, lateral orbitofrontal, and middle temporal. Mediation analysis revealed that increased immune response and glucose levels are common pathways linking shift work to these disorders. We observed diversity in shift work tolerance across different individual characteristics, among which socioeconomic status and length of working hours were the most essential.

LIMITATIONS

Self-reported employment information may cause misclassification and recall bias. And since we focused on the middle-aged population, the conclusions may not be representative of younger or older populations.

CONCLUSIONS

Our findings indicated the need to monitor shift worker health and provide personalized management to help adapt to shift work.

Impact of shift work on dementia: a systematic review and dose-response meta-analysis

OBJECTIVES

Although shift work has been reported as having a link to dementia, evidence remains inconsistent, and a comprehensive dose-response meta-analysis of the association is still lacking. We therefore conducted this meta-analysis to explore the association between shift work and the risk of dementia.

STUDY DESIGN

Systematic review and dose-response meta-analysis.

METHODS

PubMed, Embase, and Web of Science databases were systematically searched. Fixed or random-effects models were used to estimate the summary relative risks (RRs) and 95% confidence intervals (95% CIs). Generalized least squares regression was used to estimate dose-response associations, and restricted cubic splines were used to examine possible linear or non-linear associations.

RESULTS

Five articles (10 studies) with 72,999 participants and 23,067 cases were eventually included in the meta-analysis. The summary RRs and 95% CIs of dementia risk with shift work and night shift work versus daytime work were 1.13 (95% CI: 1.05-1.21, I2 = 46.70%) and 1.13 (95% CI: 1.03-1.24, I2 = 9.20%), respectively. The risk of dementia increased by 1% (RR = 1.01, 95% CI: 1.01-1.02, I2 = 41.3%) with each 1-year increase in the duration of shift work. We found a non-linear dose-response association between the duration of shift work and the risk of dementia (Pnon-linearity = 0.006). Though the shape of the curve was steeper with the duration of shift work <7 years, the increase was more gradual after 7 years.

CONCLUSION

Our findings suggest that shift work may be a risk factor for future dementia and that controlling the length of shift work is a feasible measure that may contribute to prevent dementia.

Association of Night Shifts and Lifestyle Risks With Incident Dementia

BACKGROUND

Little is known about the combined relationship between night shifts and lifestyle risks with incident dementia or their potential interactions. To evaluate the association of night shifts and lifestyle risks with incident dementia and further analyze their interactions.

METHODS

A total of 276 059 participants were included in this study from the UK Biobank cohort. Cox proportional hazards models were used to investigate the combined association of night shifts and lifestyle risks with incident dementia.

RESULTS

Participants with always night shifts and 3 or 4 unhealthy lifestyle factors had the highest risk of incident all-cause dementia (hazard ratio: 3.15, 95% confidence interval [CI]: 1.74-5.69). An additive interaction was found between night shifts and lifestyle risks for incident all-cause dementia (p < .001), with a relative excess risk due to the interaction of 0.14 (95% CI: 0.11-0.45). The attributable proportions of the combined effect on the incidence of all-cause dementia were 22.6% (95% CI: 20.91%-26.75%) for night shift work, 65.0% (95% CI: 63.12%-69.80%) for unhealthy lifestyle factors, and 12.1% (95% CI: 8.67%-18.04%) for their interaction.

CONCLUSIONS

Both night shifts and lifestyle risks were associated with a higher risk of incident dementia. The combined impact was higher than the increase in the risks related to each single factor. Our results indicated that most incident dementia cases might be prevented by a healthy lifestyle, and the benefits would be greater among night shift workers. Further studies are needed to confirm our results and explore the underlying mechanisms.

Consequences of Shift Work and Night Work: A Literature Review

Nonstandard work schedules such as shift work and night work tend to trigger problems for workers in different areas. To illustrate the diversity of areas affected and the relative interest of the scientific community, we conducted a literature review of the effects of shift work and night work on workers. In particular, we intended to identify the main variables addressed in the field of health, the family sphere, and the organizational context. The literature review was carried out using the Web of Science with the following terms: "shift work", "rotating shifts", and "night work". Inclusion criteria incorporated empirical studies and articles written in Portuguese or English published in 2019. We selected 129 of the 619 articles identified. Regarding the impacts of shift work and night work, there existed a high discrepancy of focus between the three defined areas: health, family life, and organizational context. Specifically, health-related variables were the most studied (83.4%), followed by organizational variables (9.2%), and, lastly, family variables (7.4%). Based on these results, it is essential to extend the study of the two underrepresented impacts to other crucial areas, not only for the worker but also for organizations.

Shift work is significantly and positively associated with dementia: A meta-analysis study

Background

Shift work may disrupt the sleep and wake cycles and negatively affect physical and mental health. Dementia is a neurodegenerative disorder with progressively declining cognition that is receiving increasing attention. Studies on the association between shift work and dementia are rare. Herein, we conducted a meta-analysis to investigate the association between shift work and dementia.

Materials and methods

This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched the PubMed, Embase, and Web of Science databases using a related set of keywords. The inclusion criteria were as follows: (1) adult employees working in a factory, company, or organization; (2) exposure to shift work/non-shift work; and (3) outcome of dementia based on examination or assessment. A meta-analysis using a fixed-effects model was performed. The hazard ratio of dementia was compared between shift workers and non-shift workers.

Results

Five studies were included in the quantitative synthesis, and two were selected for further meta-analysis. A random-effects model showed a modest association between shift work and an increase in dementia cases (pooled hazard ratio = 1.13; 95% confidence interval: 1.04-1.23; p = 0.04). This association also occurred in night workers for more than 1 year.

Conclusion

Shift work and long-term night work were modestly associated with a higher risk of developing dementia. Avoiding long-term night shifts may be effective in reducing dementia risk. Further studies are required to confirm this hypothesis.

Measurements of cerebrospinal fluid production: a review of the limitations and advantages of current methodologies

Cerebrospinal fluid (CSF) is an essential and critical component of the central nervous system (CNS). According to the concept of the "third circulation" originally proposed by Cushing, CSF is mainly produced by the choroid plexus and subsequently leaves the cerebral ventricles via the foramen of Magendie and Luschka. CSF then fills the subarachnoid space from whence it disperses to all parts of the CNS, including the forebrain and spinal cord. CSF provides buoyancy to the submerged brain, thus protecting it against mechanical injury. CSF is also transported via the glymphatic pathway to reach deep interstitial brain regions along perivascular channels; this CSF clearance pathway promotes transport of energy metabolites and signaling molecules, and the clearance of metabolic waste. In particular, CSF is now intensively studied as a carrier for the removal of proteins implicated in neurodegeneration, such as amyloid-β and tau. Despite this key function of CSF, there is little information about its production rate, the factors controlling CSF production, and the impact of diseases on CSF flux. Therefore, we consider it to be a matter of paramount importance to quantify better the rate of CSF production, thereby obtaining a better understanding of CSF dynamics. To this end, we now review the existing methods developed to measure CSF production, including invasive, noninvasive, direct, and indirect methods, and MRI-based techniques. Depending on the methodology, estimates of CSF production rates in a given species can extend over a ten-fold range. Throughout this review, we interrogate the technical details of CSF measurement methods and discuss the consequences of minor experimental modifications on estimates of production rate. Our aim is to highlight the gaps in our knowledge and inspire the development of more accurate, reproducible, and less invasive techniques for quantitation of CSF production.

Relationship between shift work, night work, and subsequent dementia: A systematic evaluation and meta-analysis

Background

The association between shift work, night work, and the risk of dementia are conflicting in the literature.

Objectives

This study was performed to obtain evidence on the potential relationship between shift work, night work, and dementia.

Methods

To investigate the link between shift work, night work, and dementia, we systematically searched PubMed, Embase, and Web of Science from inception to January 1, 2022. The eligibility of the retrieved records and extracted data were independently reviewed by two researchers. The Preferred Reporting Items for Systematic Evaluations and Meta-Analyses (PRISMA) statement was followed. STATA 16.0 was used to conduct the meta-analysis.

Results

A total of four studies involving 103,104 participants were included in this meta-analysis. Pooled results indicated that night shift workers had a 12% increased risk of dementia compared to subjects without night work (HR = 1.12, 95% CI 1.03–1.23, P = 0.094). Shift work was not significantly associated with dementia risk (HR: 1.09, 95% CI: 0.83–1.43, P = 0.546), but the effect of shift work on dementia risk appeared to increase with age, with a correlation observed among workers older than 50 years (HR = 1.31; 95% CI: 1.03–1.68, P = 0.030).

Conclusion

The data presented in our study suggest that night work may be a risk factor for dementia. More prospective studies with objective exposure measurements are required to further confirm this result.

Systematic review registration

https://doi.org/10.37766/inplasy2022.6.0079, identifier: INPLASY202260079.

Does Long-Term Shift Work Increase the Risk of Dementia? A Systematic Review and Meta-Analysis

Background: Shift work is associated with impaired sleep quality and disrupted circadian rhythms, but the way in which it increases the risk of dementia remains controversial. We conducted a systematic review and meta-analysis to assess the integrated risk of dementia with shift work. Methods: Searching in PubMed, Cochrane Library, and the Web of Science databases, the relative risks of dementia with shift work were extracted from 12 included studies with 3975 dementia cases from 84 492 participants. The subgroup analysis was stratified by age, gender, sample size, dementia cases, shift schedule, occupation, and follow-up time. Heterogeneity analysis and publication bias analysis were conducted for quality control. Results: The pooled risk ratios (RRs) of dementia with shift work were 1.15 (95%CI = 1.02-1.30). The subgroup analysis found that continuous evening shifts reversibly reduced the risk, but continuous night shifts remarkedly increased the risk of dementia. In addition, a larger cohort and longer follow-up significantly increased the risk of dementia with shift work. Conclusion: Shift work shows mild increases in the risk of dementia using meta-analysis.

Association of Occupational Factors and Dementia or Cognitive Impairment: A Systematic Review and Meta-Analysis

BACKGROUND

Several existing studies have reported that occupational factors might play an important part in cognitive function with aging.

OBJECTIVE

We aim to explore the associations between modifiable occupational factors and risk of dementia or mild cognitive impairment (MCI).

METHODS

Adopting random-effect models, this study conducted primary analyses for all occupational factors and subgroup analyses for the effect of occupation type based on prospective cohort and case-control studies searched from PubMed and EMBASE databases up to March 2020.

RESULTS

Among the 38,111 identified literatures, 9 studies on occupation type, 4 studies on work complexity, and 30 studies on occupational exposure were included. In terms of occupation type, mental work conferred a 44% reduced risk (95% CI = 0.34-0.94, I² = 85.00%, p < 0.01) for MCI. In terms of work complexity, higher work complexity conferred a 5% reduced risk (95% CI = 0.91-1.00, I² = 57.00%, p < 0.01) for dementia. In terms of occupational exposure, high strain and passive job in the longest-held job conferred a 1.21- and 1.15-fold excess risk (95% CI = 1.05-1.39 I² = 62.00%, p < 0.05; 95% CI = 1.05-1.26 I² = 31.00%, p = 0.23; respectively) of cognitive decline. Besides, magnetic field exposure conferred a 1.26-fold excess risk (95% CI = 1.01-1.57, I² = 69.00%, p < 0.01) for dementia.

CONCLUSION

Novel prevention strategies based on occupational factors may hold promise against dementia and MCI.

Impact of Shift Work and Long Working Hours on Worker Cognitive Functions: Current Evidence and Future Research Needs

Particular working conditions and/or organization of working time may cause important sleep disturbances that have been proposed to be predictive of cognitive decline. In this regard, circadian rhythm misalignment induced by exposure to night work or long working hours would be responsible for cognitive impairment. Nevertheless, evidence supporting this correlation is limited and several issues still need to be elucidated. In this regard, we conducted a systematic review to evaluate the association between shift/night work and cognitive impairment and address its main determinants. Information provided by the reviewed studies suggested that night work might have serious immediate negative effects especially on cognitive domains related to attention, memory and response inhibition. Furthermore, cognitive performance would progressively worsen over consecutive night shifts or following exposure to very long work shifts. Otherwise, conflicting results emerged regarding the possible etiological role that night work chronic exposure would have on cognitive impairment. Therefore, circadian rhythm desynchronization, lack of sleep and fatigue resulting from night work may negatively impact worker’s cognitive efficiency. However, in light of the considerable methodological variability of the reviewed studies, we proposed to develop a standardized research and evaluation strategy in order to obtain a better and comprehensive understanding of this topic.

The Multi-Partner Consortium to Expand Dementia Research in Latin America (ReDLat): Driving Multicentric Research and Implementation Science

Dementia is becoming increasingly prevalent in Latin America, contrasting with stable or declining rates in North America and Europe. This scenario places unprecedented clinical, social, and economic burden upon patients, families, and health systems. The challenges prove particularly pressing for conditions with highly specific diagnostic and management demands, such as frontotemporal dementia. Here we introduce a research and networking initiative designed to tackle these ensuing hurdles, the Multi-partner consortium to expand dementia research in Latin America (ReDLat). First, we present ReDLat's regional research framework, aimed at identifying the unique genetic, social, and economic factors driving the presentation of frontotemporal dementia and Alzheimer's disease in Latin America relative to the US. We describe ongoing ReDLat studies in various fields and ongoing research extensions. Then, we introduce actions coordinated by ReDLat and the Latin America and Caribbean Consortium on Dementia (LAC-CD) to develop culturally appropriate diagnostic tools, regional visibility and capacity building, diplomatic coordination in local priority areas, and a knowledge-to-action framework toward a regional action plan. Together, these research and networking initiatives will help to establish strong cross-national bonds, support the implementation of regional dementia plans, enhance health systems' infrastructure, and increase translational research collaborations across the continent.

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.

Long work hours, prolonged daytime naps, and decreased cognitive performance in older adults

In the United States, labor force market projections show significant growth in older ages. With postponed retirement and age-related health changes, attention to work times and recuperative strategies related to cognitive performance remains necessary for safe practice. The purpose of this study was to explore the relationships between long work hours, daytime naps, and cognitive performance in older adults. Cross-sectional data were obtained from 2013-2014 waves of the National Health and Aging Trends Study. A total sample of 308 workers were identified that had data on work hours, sleep-related parameters, and cognitive functioning. Around 42% of older adults were 70 to 74 years of age, and almost 73% of the sample worked < 40 hours/week. Workers on average slept 6.87 ± 1.27 hours, and nearly 43% reported daytime napping, with most naps being brief (≤ 45 minutes). Around 78% of the sample showed no signs of cognitive impairment. After controlling for covariates, older adults who worked ≥ 40 hours/week, compared to older adults who worked < 40 hours, had 2.07 (95%CI 1.03-4.18) increased odds for decreased cognitive performance. Older adults who took prolonged daytime naps (> 45 minutes), compared to those who took no naps, had 2.20 (95%CI 1.00-4.83) increased odds for decreased cognitive performance. No significant relationship was found between those who took brief daytime naps, compared to those who took no naps, and cognitive performance. Future research is needed to elucidate further the possible longitudinal effects of work times and daytime naps, which are modifiable, on cognitive performance in the aging workforce.

The Future of Shift Work: Circadian Biology Meets Personalised Medicine and Behavioural Science

Shift work is commonplace in modern societies, and shift workers are predisposed to the development of numerous chronic diseases. Disruptions to the circadian systems of shift workers are considered important contributors to the biological dysfunction these people frequently experience. Because of this, understanding how to alter shift work and zeitgeber (time cue) schedules to enhance circadian system function is likely to be key to improving the health of shift workers. While light exposure is the most important zeitgeber for the central clock in the circadian system, diet and exercise are plausible zeitgebers for circadian clocks in many tissues. We know little about how different zeitgebers interact and how to tailor zeitgeber schedules to the needs of individuals; however, in this review we share some guidelines to help shift workers adapt to their work schedules based on our current understanding of circadian biology. We focus in particular on the importance of diet timing and composition. Going forward, developments in phenotyping and "envirotyping" methods may be important to understanding how to optimise shift work. Non-invasive, multimodal, comprehensive phenotyping using multiple sources of time-stamped data may yield insights that are critical to the care of shift workers. Finally, the impact of these advances will be reduced without modifications to work environments to make it easier for shift workers to engage in behaviours conducive to their health. Integrating findings from behavioural science and ergonomics may help shift workers make healthier choices, thereby amplifying the beneficial effects of improved lifestyle prescriptions for these people.

Shift work and incidence of dementia: A Danish Nurse Cohort study

INTRODUCTION

A few studies suggest that working night and rotating shifts increase the risk of dementia. We examined the association between shift work and the incidence of dementia in a cohort of female Danish nurses.

METHODS

We linked Danish Nurse Cohort participants, who reported work schedules (day, evening, night, rotating shifts) in 1993 and/or 1999 and their duration in 2009, to Danish registers to obtain information on dementia hospitalizations and prescription medication until November 2018.

RESULTS

Among 6048 nurses who reported work schedules in 1993 and 1999, nurses working night shifts ≥6 years had higher dementia incidence (hazard ratio: 2.43, 95% confidence interval: 1.39 to 4.23) than those working day shifts ≥6 years. Among 8059 nurses who reported shift work duration, nurses working night shifts ≥6 years had higher dementia incidence than those working night shifts <1 year (1.47, 1.06 to 2.06).

DISCUSSION

Persistent night shift work may increase the risk of dementia.

Night work and risk of ischaemic heart disease and anti-hypertensive drug use: a cohort study of 145 861 Danish employees

Background

Ischaemic heart disease (IHD) and hypertension are leading causes of mortality and night work has been suspected as a risk factor. Meta-analyses and previous studies are often limited by power and various definitions of exposure and outcomes. This study aimed to investigate if night work increases the risk of IHD or anti-hypertensive drug usage in a large cohort of Danish employees.

Methods

Individual participant data on night work were drawn from the Danish Labour Force Survey (1999–2013). We included 145 861 participants (53% men) 21–59 years of age working 32 h or more per week. Participants with diagnosis or drug use in the year prior to baseline were excluded. Data on outcomes were obtained from nationwide health registers. Using Poisson regression we analyzed incidence rates of the outcomes as functions of night work adjusted for relevant covariates.

Results

We observed 3635 cases of IHD and 20 648 cases used anti-hypertensive drugs. When examining main effects the association of night work with drug use was estimated at rate ratio (RR): 1.05 (95% CI: 1.01–1.09). A sensitivity analysis suggested a dose-response association. The association of night work with IHD was estimated at RR: 1.08 (95% CI: 0.98–1.19). Overall likelihood ratio test showed no statistically significant associations between night work and IHD or drug use when including interactions with sex and socioeconomic status.

Conclusions

Night work was associated with an increased risk of anti-hypertensive drug use. Small estimates suggested a dose-response association. No statistically significant association between night work and IHD were found.