IARC 2019: "Night shift work" is probably carcinogenic: What about disturbed chronobiology in all walks of life?

The Impact of Night Work on the Sleep and Health of Medical Staff-A Review of the Latest Scientific Reports

Introduction: Employees working in shifts are exposed to many threats affecting their health, quality of life and safety at work. Those who perform their work only at night are particularly vulnerable. The purpose of the review is to identify risks to the health, quality of life and sleep of shift health workers. Method: A systematic review (SR) was used in the analysis. Electronic databases were searched. The search was limited to the latest studies published in the last five years: 2019-2023. Results: Finally, 36 articles were included in the review. Most authors have shown a link between sleep disturbance or its quality and shift work/night work. Moreover, a three-shift schedule was the most significant factor for poorer subjective sleep quality when compared to other work schedules. Furthermore, many authors have shown a link between shift/night work and health problems, which include cardiometabolic risk, glucose intolerance, breast cancer and immune vulnerability. Conclusions: The research results clearly show a significant impact of night work on the increased risk of sleep disorders and health disturbance. Healthcare workers should be aware of the risks associated with night work in order to take measures preventing sleep/health problems. Shift/night workers should have the opportunity to be screened for disorders linked with their work.

Extracellular Vesicles, Circadian Rhythms, and Cancer: A Comprehensive Review with Emphasis on Hepatocellular Carcinoma

This review comprehensively explores the complex interplay between extracellular vesicles (ECVs)/exosomes and circadian rhythms, with a focus on the role of this interaction in hepatocellular carcinoma (HCC). Exosomes are nanovesicles derived from cells that facilitate intercellular communication by transporting bioactive molecules such as proteins, lipids, and RNA/DNA species. ECVs are implicated in a range of diseases, where they play crucial roles in signaling between cells and their surrounding environment. In the setting of cancer, ECVs are known to influence cancer initiation and progression. The scope of this review extends to all cancer types, synthesizing existing knowledge on the various roles of ECVs. A unique aspect of this review is the emphasis on the circadian-controlled release and composition of exosomes, highlighting their potential as biomarkers for early cancer detection and monitoring metastasis. We also discuss how circadian rhythms affect multiple cancer-related pathways, proposing that disruptions in the circadian clock can alter tumor development and treatment response. Additionally, this review delves into the influence of circadian clock components on ECV biogenesis and their impact on reshaping the tumor microenvironment, a key component driving HCC progression. Finally, we address the potential clinical applications of ECVs, particularly their use as diagnostic tools and drug delivery vehicles, while considering the challenges associated with clinical implementation.

Protective Effects of Melatonin against Carcinogen-Induced Oxidative Damage in the Thyroid

Melatonin, primarily synthesized in the pineal gland, plays a crucial role in regulating circadian rhythms and possesses significant antioxidative properties. By neutralizing free radicals and reducing oxidative stress, melatonin emerges as a promising agent for the prevention and therapy of many different disorders, including cancer. This paper reviews the relationship between the thyroid gland and melatonin, presenting experimental evidence on the protective effects of this indoleamine against oxidative damage to macromolecules in thyroid tissue caused by documented carcinogens (as classified by the International Agency for Research on Cancer, IARC) or caused by potential carcinogens. Furthermore, the possible influence on cancer therapy in humans and the overall well-being of cancer patients are discussed. The article highlights melatonin's essential role in maintaining thyroid health and its contribution to management strategies in patients with thyroid cancer and other thyroid diseases.

A cross-sectional analysis of the association between sleep disorders and cancer using data from the National Health and Nutrition Examination Survey (NHANES) 2005-2014

STUDY OBJECTIVES

Cancer is one of the main causes of death in the world, and sleep disorders are a serious public health problem, especially in large cities; of these, insomnia and obstructive sleep apnea (OSA) are the most common. In the last decade, studies have pointed to a possible association between sleep disorders and cancer. The aim of this study is to evaluate whether there is any association between sleep disorders and cancer.

METHODS

Five National Health and Nutrition Examination Surveys (NHANES) (2005-2014) from the United States were combined in order to obtain the sample. Two main sleep variables were assessed: having trouble sleeping and/or ever telling a doctor one had a sleep problem. The odds ratio of ever having a cancer diagnosis was the main outcome. Data were analyzed by binary logistic regression models in Jamovi.

RESULTS

The final sample comprised 26,821 participants. Individuals who reported having trouble sleeping had an odds ratio of 1.48 (95% confidence interval = [1.336-1.646]; P < .001) of having been diagnosed with cancer, and those who had already been diagnosed with a sleep disorder had an odds ratio of 1.21 (95% confidence interval = [1.046-1.415]; P = .011), showing an increased chance of having been diagnosed with cancer. In men, these values were even greater, with an odds ratio of 1.56 (95% confidence interval = [1.321-1.843]; P < .001) and an odds ratio of 1.26 (95% confidence interval = [1.013-1.582]; P = .037), respectively, for having trouble sleeping and for having been diagnosed with a sleep disorder, in relation to having been diagnosed with cancer.

CONCLUSIONS

Individuals who had trouble sleeping or who had been diagnosed with a sleep disorder at any time in their life were more likely to have been diagnosed with cancer.

CITATION

Porcacchia AS, Pires GN, Andersen ML, Tufik S. A cross-sectional analysis of the association between sleep disorders and cancer using data from the National Health and Nutrition Examination Survey (NHANES) 2005-2014. J Clin Sleep Med. 2024;20(4):515-520.

Considering the impact of shift working on health

Shift work is necessary for the provision of health services, especially in hospitals as it is the only way to provide continuous care to patients. Working at night is inconsistent with the body's biological clock and night shift working hugely disrupts the circadian and sleep wake cycles. In 2020, the World Health Organization classified night shift working as being a 'probable' class 2A carcinogen and a number of independent cohort studies of both night workers and shift workers have observed increased incidence of certain cancers. Altered sleep timing, food timing and light exposure typical for shift workers leads to an acute circadian disruption and misalignment of regulatory hormones. This straying from synchronisation has been shown to result in individuals being more vulnerable to a number of chronic health conditions. Night shift work disrupts the normal sleep-wake cycle, often leading to shortened sleep duration and excessive fatigue and the results of this are far reaching. This article will explore the full impact of shift working, questioning if current practices employed within the NHS should continue.

Circadian epidemiology: Structuring circadian causes of disease and practical implications

That disruptions of the body's internal clockwork can lead to negative health consequences, including cancer, is a plausible hypothesis. Yet, despite strong mechanistic and animal support, the International Agency for Research on Cancer (IARC) experts considered epidemiological evidence as limited regarding the carcinogenicity of "shift-work involving circadian disruption" (2007) and "night shift work" (2019). We use directed acyclic graphs (DAGs) to outline a concept of circadian causes that discloses challenges when choosing appropriate exposure variables. On this basis, we propose to move beyond shift-work alone as a direct cause of disease. Instead, quantifying chronodisruption as individual doses can lead to interpretable circadian epidemiology. The hypothesis is that doses of chronodisruption cause disrupted circadian organisation by leading to desynchronization of circadian rhythms. Chronodisruption can be conceptualized as the split physiological nexus of internal and external times. Biological (or internal) night - an individual's intrinsically favoured sleep time window - could be the backbone of circadian epidemiology. In practice, individual doses that cause disrupted circadian organisation are derived from the intersection of time intervals of being awake and an individual's biological night. After numerous studies counted work shifts, chronobiology may now advance circadian epidemiology with more specific dose estimation - albeit with greater challenges in measurement (time-dependent individual data) and analysis (time-dependent confounding).

Evaluation of orderliness of underground workplace system based on occupational ergonomics: A case study in Guangzhou and Chengdu metro depots

BACKGROUND

An underground workplace (UGW) is a complex system with multiple subsystems that interact with each other. However, the research on UGW from a systemic perspective has not received due attention.

OBJECTIVE

This study constructs an evaluation approach to the orderliness of UGW and systematically evaluates the UGW with Guangzhou and Chengdu metro depots as case studies.

METHODS

First, the evaluation index system is established based on occupational ergonomics. Second, the system entropy model is constructed based on information entropy. Third, a dissipative structure judgment model is built based on the Brusselator. Fourth, the orderliness evaluation model is constructed based on information entropy and synergetics.

RESULTS

The UGW of the metro depot has not yet reached the dissipative structure and is in a medium-order state. But the system is in the trend of orderly development. The entropy increase caused by the physical environment and health status is the main obstacle for the system to move toward order. The equipment configuration is an essential source of system negative entropy. The coordination between equipment configuration, health status, and physical environment is low, and that of work effectiveness, equipment aging and failure, and organizational environment is high.

CONCLUSIONS

Equipment configuration cannot fully cope with the harsh physical environment and meet the needs of underground workers. Safety security equipment has more room for improvement. Humanized support facilities can introduce more negative entropy to the system. Organizational intervention can reduce the negative impact of adverse factors on the system.

Increased breast cancer incidence among nurses in a tertiary university hospital in South Korea

Background

A series of breast cancer cases were recently reported in a tertiary university hospital in South Korea. Nurses are generally exposed to risk factors for breast cancer such as night shift work, antineoplastic agents, and job strain. However, the epidemiological evidence of excess incidence among nurses remains lacking. This study aims to investigate the excess incidence of breast cancer among nurses in a tertiary university hospital and provide epidemiological evidence of occupational risk factors.

Methods

A retrospective cohort was developed using personnel records of female workers in the nursing department who worked from January 2011 to June 2021 in a tertiary university hospital in South Korea. Sick leave records were used to identify cases of breast cancer. The standardized incidence ratio of breast cancer among nurses was compared to the general population.

Results

A total of 5,509 nurses were followed up for 30,404 person-years, and 26 breast cancer cases were identified. This study revealed a significantly increased breast cancer incidence among all included nurses, with a standardized incidence ratio of 1.65 (95% confidence interval [CI]: 1.08-2.41), compared to the general population. Workers, who handle antineoplastic agents in their representative department and current and/or former department, had significantly elevated breast cancer standardized incidence ratios of 2.73 (95% CI: 1.008-5.94) and 3.39 (95% CI: 1.46-6.68), respectively.

Conclusions

This study provides significant evidence of increased breast cancer risk among nursing staff in a hospital setting, particularly those who handle antineoplastic drugs. Measures that reduce exposure to risk factors should be implemented, especially anticancer drugs, to protect healthcare professionals. Further research at a national level that focuses on healthcare workers is necessary to validate breast cancer incidence and its contributing factors.

A new time dimension in the fight against metastasis

Despite advances in uncovering vulnerabilities, identifying biomarkers, and developing more efficient treatments, cancer remains a threat because of its ability to progress while acquiring resistance to therapy. The circadian rhythm governs most of the cellular functions implicated in cancer progression, and its exploitation therefore opens new promising directions in the fight against metastasis. In this review we summarize the role of the circadian rhythm in tumor development and progression, with emphasis on the circadian rhythm-regulated elements that control the generation of circulating tumor cells (CTCs) and metastasis. We then present data on chronotherapy and discuss how circadian rhythm investigations may open new paths to more effective anticancer treatments.

Light on Shedding: A Review of Sex and Menstrual Cycle Differences in the Physiological Effects of Light in Humans

The human circadian system responds to light as low as 30 photopic lux. Furthermore, recent evidence shows that there are huge individual differences in light sensitivity, which may help to explain why some people are more susceptible to sleep and circadian disruption than others. The biological mechanisms underlying the differences in light sensitivity remain largely unknown. A key variable of interest in understanding these individual differences in light sensitivity is biological sex. It is possible that in humans, males and females differ in their sensitivity to light, but the evidence is inconclusive. This is in part due to the historic exclusion of women in biomedical research. Hormonal fluctuations across the menstrual cycle in women has often been cited as a confound by researchers. Attitudes, however, are changing with funding and publication agencies advocating for more inclusive research frameworks and mandating that women and minorities participate in scientific research studies. In this article, we distill the existing knowledge regarding the relationship between light and the menstrual cycle. There is some evidence of a relationship between light and the menstrual cycle, but the nature of this relationship seems dependent on the timing of the light source (sunlight, moonlight, and electric light at night). Light sensitivity may be influenced by biological sex and menstrual phase but there might not be any effect at all. To better understand the relationship between light, the circadian system, and the menstrual cycle, future research needs to be designed thoughtfully, conducted rigorously, and reported transparently.

Analysis and mapping of global research publications on shift work (2012-2021)

BACKGROUND

The main objective of the study was to identify research trends, collaboration patterns, and the most impactful publications in the field of shift work.

METHODS

Documents published in scientific journals indexed in the Scopus database on shift work were retrieved and analyzed using the title/abstract search methodology. The study period was from January 1st, 2012, to December 31st, 2021.

RESULTS

Two thousand three hundred twenty-eight documents were retrieved with an h-index of 71 and an average number of 4.5 authors per document. The cumulative number of publications showed a linear growth pattern, while that of citations showed an exponential pattern. The most frequent author keywords, excluding keywords related to shift work, were sleep, fatigue, and nursing. The average annual growth rate was 4.3, and the average doubling time was 3.2. No significant correlation was found between the number of publications and national income among prolific countries. Cross-country research collaboration was weak while the degree of author-author collaboration was relatively high. The Chronobiology International journal was the most prolific, while Harvard University was the most active institution in the field of shift work.

CONCLUSIONS

Given the volume and the negative health impact of shift work, better human resource management is needed to create safer and healthier working schedules.

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

Background

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

Methods

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

Results

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

Conclusions

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

Review of Under-Recognized Adjunctive Therapies for Cancer

Patients and providers may not be aware that several adjunctive measures can significantly improve the quality of life, response to treatment, and possibly outcomes for cancer patients. This manuscript presents a review of practical under-recognized adjunctive therapies that are effective including exercise; stress-reduction techniques such as mindfulness, massage, yoga, Tai Chi, breathing exercises; importance of sleep quality; diet modifications such as calorie restriction at the time of chemotherapy and avoidance of high carbohydrate foods; supplements such as aspirin, green tea, turmeric, and melatonin; and repurposed prescription medications such as metformin and statins. Each recommendation should be tailored to the individual patient to assure no contraindications.

Work as a Social Determinant of Racial Health Inequalities

Interdisciplinary research posits that work is a social determinant of health contributing to racial inequalities in death, disease, and well-being amongst Black individuals in the United States. This study aims to advance research by integrating two theoretical frameworks (Warr's Vitamin Model and Assari's "differential exposure" and "differential gain" mechanisms) to investigate the role of work in eudemonic well-being. We included a nationally representative sample of adults who participated in the Midlife in the United States (MIDUS) Refresher and Milwaukee Refresher projects in 2011-2014, alongside corresponding occupational information (O*NET 17.0). The results of this study indicated that three of nine studied job characteristics systematically differ by race. We found evidence of differential gain by race on psychological well-being. Job characteristics had either benign or negative associations with well-being among Black individuals but consistently positive associations with well-being among non-Black individuals. In contrast to Warr's Vitamin Model, we found little evidence of curvilinear health effects of job characteristics (only 5.5% were statistically significant). Finally, it was found that advanced educational attainment benefited multiple dimensions of well-being among Black individuals but had benign or negative implications for non-Black individuals, after controlling for demographics. Overall, the results highlight racial inequalities in eudemonic well-being because Black individuals face challenges in obtaining jobs that are beneficial to well-being. Collectively, the results reinforce the idea that work is a social determinant of health.

Sleep duration, chronotype, and insomnia and the risk of lung cancer: United Kingdom Biobank Cohort

BACKGROUND

Relationships between sleep duration, chronotype, insomnia and lung cancer risk have not been comprehensively examined. Inter-relations between sleep traits on the risk of lung cancer have not been assessed. We aimed to examine sleep traits with lung cancer risk.

METHODS

Participants were recruited between 2006 - 2010 and followed through November 30th, 2020. We included 382,966 participants (3,664 incident lung cancer) in analysis. Cox proportional hazards models estimated hazards ratios (HR) and 95% confidence intervals (CI) for associations between sleep duration, chronotype, and insomnia symptoms and lung cancer risk. Joint effects analyses were examined between sleep duration and three traits (chronotype,insomnia,daytime napping). Non-linear associations between sleep duration and lung cancer risk were assessed in restricted cubic spline analysis.

RESULTS

Longer sleep (>8 hours) was positively associated with lung cancer risk compared with normal sleep duration (7-8 hours; HR=1.22; 95% CI: 1.10, 1.36). Frequent insomnia symptoms increased the risk of lung cancer compared with never/rarely experiencing symptoms (HR= 1.16; 95% CI: 1.05, 1.28). Joint effects between sleep duration and chronotype, and sleep duration and insomnia symptoms were observed. In analysis excluding participants reporting shift work at baseline, evening chronotypes ('slight', 'definite') were at a greater risk of lung cancer compared with definite morning chronotype (HR=1.17; 95% CI: 1.06, 1.28 and HR=1.37; 95% CI: 1.21, 1.54, respectively).

CONCLUSIONS

Sleep traits such as long sleep duration, frequent insomnia symptoms, and definite evening chronotype may be risk factors for lung cancer. Joint effects should be further investigated.

IMPACT

Sleep traits may be risk factors of lung cancer.

Current Insights into Optimal Lighting for Promoting Sleep and Circadian Health: Brighter Days and the Importance of Sunlight in the Built Environment

This perspective considers the possibility that daytime's intrusion into night made possible by electric lighting may not be as pernicious to sleep and circadian health as the encroachment of nighttime into day wrought by 20th century architectural practices that have left many people estranged from sunlight.

Association of industrial work schedules with development of metabolic syndrome, insulin resistance, and serum adipokine concentrations

Background

Association of work schedule in industrial workers with the progression of metabolic syndrome, insulin resistance, and serum adipokine concentrations is incompletely explored.

Objective

To determine the association of work schedule with the progression of metabolic syndrome, insulin resistance, and adipokine concentrations in industrial workers.

Methods

In a cross-sectional study design of industrial workers we compared metabolic syndrome, insulin resistance, and adipokines concentration between workers in the day shift (n = 52), rotational shift (n = 21), and night shift (n = 15). The international Diabetes Federation criteria were used to diagnose metabolic syndrome. We used a homeostatic model assessment of insulin resistance (HOMA-IR). Serum insulin, leptin, and adiponectin concentrations were measured using enzyme-linked immunosorbent assays. Serum glucose, triglyceride, and high-density lipoprotein cholesterol (HDL-C) concentrations were monitored using Prietest clinical chemistry reagents.

Results

The proportional difference in metabolic syndrome (0.31, 95% confidence interval [CI] 0.036-0.587, P = 0.026), median difference of leptin (0.61, 95% CI 0.186-1.034, P = 0.005), and leptin-to-adiponectin ratio (LAR; 0.45, 95% CI 0.235-0.665, P < 0.001) was significantly higher, and serum adiponectin was lower (-2.00, 95% CI -4.197 to 0.197, P = 0.07) in the night-shift workers compared with that of day-shift workers. Among rotational-shift workers, the proportional difference between metabolic syndrome (0.14, 95% CI -0.098 to 0.378, P = 0.25), median difference of leptin (0.25, 95% CI -0.124 to 0.624, P = 0.19), and LAR (0.09, 95% CI -0.099 to 0.279, P = 0.35) was higher, and serum adiponectin concentration was lower (-0.73, 95% CI -2.660 to 1.208, P = 0.46) compared with that of day-shift workers; however, the altered differences were not significant. We observed a higher proportion of difference in HOMA-IR in shift workers (night and rotation) than in day-shift workers.

Conclusion

Night-shift workers are vulnerable to a higher risk of metabolic syndrome, HOMA-IR, and adipokine changes.

Clock at the Core of Cancer Development

To synchronize various biological processes with the day and night cycle, most organisms have developed circadian clocks. This evolutionarily conserved system is important in the temporal regulation of behavior, physiology and metabolism. Multiple pathological changes associated with circadian disruption support the importance of the clocks in mammals. Emerging links have revealed interplay between circadian clocks and signaling networks in cancer. Understanding the cross-talk between the circadian clock and tumorigenesis is imperative for its prevention, management and development of effective treatment options. In this review, we summarize the role of the circadian clock in regulation of one important metabolic pathway, insulin/IGF1/PI3K/mTOR signaling, and how dysregulation of this metabolic pathway could lead to uncontrolled cancer cell proliferation and growth. Targeting the circadian clock and rhythms either with recently discovered pharmaceutical agents or through environmental cues is a new direction in cancer chronotherapy. Combining the circadian approach with traditional methods, such as radiation, chemotherapy or the recently developed, immunotherapy, may improve tumor response, while simultaneously minimizing the adverse effects commonly associated with cancer therapies.

Night Shift Work, Chronotype, Sleep Duration, and Prostate Cancer Risk: CAPLIFE Study

To analyze the association between prostate cancer (PCa) risk and night shift work, chronotype, and sleep duration in the context of a population-based case-control study of incident prostate cancer in Spain, a total of 465 PCa cases and 410 controls were analyzed. Selection criteria were: (i) age 40-80 years, and (ii) residence in the coverage area of the reference hospitals for ≥6 months before recruitment. Exposure variables were: (i) night shift work (permanent or rotating); (ii) chronotype: morning, neither, or evening (Munich ChronoType Questionnaire) and (iii) sleep duration according to the recommendations of the American National Sleep Foundation. PCa aggressiveness was determined according to the International Society of Urology Pathology classification. Adjusted odds ratios (aOR) and 95% confidence intervals (95% CI) were estimated using logistic regression models. Night shift work was associated with PCa, aOR = 1.47 (95% CI 1.02-2.11), especially for rotating night shifts, aOR = 1.73 (95% CI 1.09-2.75). The magnitude of the association between ever night work and PCa was higher in evening subjects with aOR = 3.14 (95% CI 0.91-10.76) than in morning chronotypes with an aOR = 1.25 (95% CI 0.78-2.00). Working night shifts, especially rotating night shifts, could increase PCa risk. This risk may be higher in people with an evening chronotype.

Chronodisruption: A Poorly Recognized Feature of CKD

Multiple physiological variables change over time in a predictable and repetitive manner, guided by molecular clocks that respond to external and internal clues and are coordinated by a central clock. The kidney is the site of one of the most active peripheral clocks. Biological rhythms, of which the best known are circadian rhythms, are required for normal physiology of the kidneys and other organs. Chronodisruption refers to the chronic disruption of circadian rhythms leading to disease. While there is evidence that circadian rhythms may be altered in kidney disease and that altered circadian rhythms may accelerate chronic kidney disease (CKD) progression, there is no comprehensive review on chronodisruption and chronodisruptors in CKD and its manifestations. Indeed, the term chronodisruption has been rarely applied to CKD despite chronodisruptors being potential therapeutic targets in CKD patients. We now discuss evidence for chronodisruption in CKD and the impact of chronodisruption on CKD manifestations, identify potential chronodisruptors, some of them uremic toxins, and their therapeutic implications, and discuss current unanswered questions on this topic.