Simulated night shift work induces circadian misalignment of the human peripheral blood mononuclear cell transcriptome

Night Shift Work Associates with All-Cause and Cause-Specific Mortality: A Large Prospective Cohort Study

BACKGROUND

Health problems associated with shift work and night shift work are gaining increasing public attention.

OBJECTIVE

To investigate the association between night shift work and the hazard of mortality.

DESIGN

Prospective cohort study.

PARTICIPANTS

A total of 283,579 individuals with paid employment or self-employment aged 37-73 years were included from the UK Biobank with a median follow-up period of 14.0 years.

MAIN MEASURES

Participants were divided into day workers and shift workers, including the frequency of night shifts, to evaluate the association between baseline work schedules and all-cause and cause-specific mortality using the Cox proportional hazards model. Additionally, 75,760 participants with work histories were assessed for the association between average frequency and cumulative years of exposure to night shift work and all-cause and cause-specific mortality.

KEY RESULTS

Compared with that of day workers, the adjusted hazard of all-cause mortality was increased by 12.0% (hazard ratio [HR], 1.12; 95% confidence interval [CI], 1.07-1.18) in shift workers, particularly in those with no or rare night shifts (approximately 16.1%; HR, 1.16; 95% CI, 1.08-1.25) and those with irregular night shifts (approximately 9.2%; HR, 1.09; 95% CI, 1.00-1.19). Moreover, a non-linear relationship was identified between cumulative night shift years and all-cause and cause-specific mortality. Only individuals who worked night shifts for 20-30 years exhibited a substantially increased hazard of all-cause (HR, 1.52; 95% CI, 1.15-2.00) and cardiovascular disease (CVD; HR, 2.08; 95% CI, 1.16-3.71) mortality.

CONCLUSIONS

Shift workers, particularly those with rare or irregular night shifts, exhibited an increased hazard of mortality. Additionally, participants who worked night shifts for 20-30 years exhibited a substantially increased hazard of all-cause and CVD mortality.

Impact of sleep disturbance in shift workers on hippocampal volume and psychomotor speed

STUDY OBJECTIVES

Shift work interferes with circadian rhythms, affecting sleep quality and cognitive function. Poor sleep quality in shift worker (SW)s can impair psychomotor performance due to fatigue and sleepiness, increasing the risk of errors, accidents, and reduced productivity. Given the potential for atrophic changes in the hippocampus due to sleep disturbances, our study investigates how poor sleep quality correlates with hippocampal structural alterations and impacts psychomotor performance among SWs.

METHODS

We recruited 100 SWs, classifying them based on sleep quality into two groups: good sleep-SW group (n = 59) and poor sleep-SW group (n = 41). Sleep quality was assessed using both 7-day actigraphy for sleep efficiency and the Pittsburgh Sleep Quality Index. A control group of 106 non-SWs without sleep problems (non-SW group) was also included for comparison. The outcome measures were psychomotor speed and hippocampal volumes, both total and by subfield.

RESULTS

The poor sleep-SW group showed significantly smaller hippocampal volumes than both the good sleep-SW group (p < .001) and the non-SW group (p = .003). Longer shift work years correlated with greater reductions in hippocampal volume in this group (r = -0.42, p = .009), unlike in the good sleep-SW group (r = 0.08, p = .541). Furthermore, they demonstrated declines in psychomotor speed relative to the non-SW group (p = .006), which correlated with smaller hippocampal volumes (r = 0.37, p = .020).

CONCLUSIONS

SWs with poor sleep quality exhibit significant hippocampal volume reductions and psychomotor speed decline, underscoring the importance of early intervention and support for sleep issues in this population.

Computational Analyses Reveal Deregulated Clock Genes Associated with Breast Cancer Development in Night Shift Workers

Breast cancer (BC) is the leading cause of cancer death among women worldwide. Women employed in shift jobs face heightened BC risk due to prolonged exposure to night shift work (NSW), classified as potentially carcinogenic by the International Agency for Research on Cancer (IARC). This risk is linked to disruptions in circadian rhythms governed by clock genes at the cellular level. However, the molecular mechanisms are unclear. This study aimed to assess clock genes as potential BC biomarkers among women exposed to long-term NSW. Clock gene expression was analysed in paired BC and normal breast tissues within Nurses' Health Studies I and II GEO datasets. Validation was performed on additional gene expression datasets from healthy night shift workers and women with varying BC susceptibility, as well as single-cell sequencing datasets. Post-transcriptional regulators of clock genes were identified through miRNA analyses. Significant alterations in clock gene expression in BC compared to normal tissues were found. BHLHE40, CIART, CLOCK, PDPK1, and TIMELESS were over-expressed, while HLF, NFIL3, NPAS3, PER1, PER3, SIM1, and TEF were under-expressed. The downregulation of PER1 and TEF and upregulation of CLOCK correlated with increased BC risk in healthy women. Also, twenty-six miRNAs, including miR-10a, miR-21, miR-107, and miR-34, were identified as potential post-transcriptional regulators influenced by NSW. In conclusion, a panel of clock genes and circadian miRNAs are suggested as BC susceptibility biomarkers among night shift workers, supporting implications for risk stratification and early detection strategies.

Higher central circadian temperature amplitude is associated with greater metabolite rhythmicity in humans

Robust circadian rhythms are essential for optimal health. The central circadian clock controls temperature rhythms, which are known to organize the timing of peripheral circadian rhythms in rodents. In humans, however, it is unknown whether temperature rhythms relate to the organization of circadian rhythms throughout the body. We assessed core body temperature amplitude and the rhythmicity of 929 blood plasma metabolites across a 40-h constant routine protocol, controlling for behavioral and environmental factors that mask endogenous temperature rhythms, in 23 healthy individuals (mean [± SD] age = 25.4 ± 5.7 years, 5 women). Valid core body temperature data were available in 17/23 (mean [± SD] age = 25.6 ± 6.3 years, 1 woman). Individuals with higher core body temperature amplitude had a greater number of metabolites exhibiting circadian rhythms (R2 = 0.37, p = .009). Higher core body temperature amplitude was also associated with less variability in the free-fitted periods of metabolite rhythms within an individual (R2 = 0.47, p = .002). These findings indicate that a more robust central circadian clock is associated with greater organization of circadian metabolite rhythms in humans. Metabolite rhythms may therefore provide a window into the strength of the central circadian clock.

Circadian disruption, clock genes, and metabolic health

A growing body of research has identified circadian-rhythm disruption as a risk factor for metabolic health. However, the underlying biological basis remains complex, and complete molecular mechanisms are unknown. There is emerging evidence from animal and human research to suggest that the expression of core circadian genes, such as circadian locomotor output cycles kaput gene (CLOCK), brain and muscle ARNT-Like 1 gene (BMAL1), period (PER), and cyptochrome (CRY), and the consequent expression of hundreds of circadian output genes are integral to the regulation of cellular metabolism. These circadian mechanisms represent potential pathophysiological pathways linking circadian disruption to adverse metabolic health outcomes, including obesity, metabolic syndrome, and type 2 diabetes. Here, we aim to summarize select evidence from in vivo animal models and compare these results with epidemiologic research findings to advance understanding of existing foundational evidence and potential mechanistic links between circadian disruption and altered clock gene expression contributions to metabolic health-related pathologies. Findings have important implications for the treatment, prevention, and control of metabolic pathologies underlying leading causes of death and disability, including diabetes, cardiovascular disease, and cancer.

Navigating Challenges and Opportunities in Multi-Omics Integration for Personalized Healthcare

The field of multi-omics has witnessed unprecedented growth, converging multiple scientific disciplines and technological advances. This surge is evidenced by a more than doubling in multi-omics scientific publications within just two years (2022-2023) since its first referenced mention in 2002, as indexed by the National Library of Medicine. This emerging field has demonstrated its capability to provide comprehensive insights into complex biological systems, representing a transformative force in health diagnostics and therapeutic strategies. However, several challenges are evident when merging varied omics data sets and methodologies, interpreting vast data dimensions, streamlining longitudinal sampling and analysis, and addressing the ethical implications of managing sensitive health information. This review evaluates these challenges while spotlighting pivotal milestones: the development of targeted sampling methods, the use of artificial intelligence in formulating health indices, the integration of sophisticated n-of-1 statistical models such as digital twins, and the incorporation of blockchain technology for heightened data security. For multi-omics to truly revolutionize healthcare, it demands rigorous validation, tangible real-world applications, and smooth integration into existing healthcare infrastructures. It is imperative to address ethical dilemmas, paving the way for the realization of a future steered by omics-informed personalized medicine.

Loss of temporal coherence in the circadian metabolome across multiple tissues during ageing in mice

Circadian clock function declines with ageing, which can aggravate ageing-related diseases such as type 2 diabetes and neurodegenerative disorders. Understanding age-related changes in the circadian system at a systemic level can contribute to the development of strategies to promote healthy ageing. The goal of this study was to investigate the impact of ageing on 24-h rhythms in amine metabolites across four tissues in young (2 months of age) and old (22-25 months of age) mice using a targeted metabolomics approach. Liver, plasma, the suprachiasmatic nucleus (SCN; the location of the central circadian clock in the hypothalamus) and the paraventricular nucleus (PVN; a downstream target of the SCN) were collected from young and old mice every 4 h during a 24-h period (n = 6-7 mice per group). Differential rhythmicity analysis revealed that ageing impacts 24-h rhythms in the amine metabolome in a tissue-specific manner. Most profound changes were observed in the liver, in which rhythmicity was lost in 60% of the metabolites in aged mice. Furthermore, we found strong correlations in metabolite levels between the liver and plasma and between the SCN and the PVN in young mice. These correlations were almost completely abolished in old mice. These results indicate that ageing is accompanied by a severe loss of the circadian coordination between tissues and by disturbed rhythmicity of metabolic processes. The tissue-specific impact of ageing may help to differentiate mechanisms of ageing-related disorders in the brain versus peripheral tissues and thereby contribute to the development of potential therapies for these disorders.

Disruption of central and peripheral circadian clocks and circadian controlled estrogen receptor rhythms in night shift nurses in working environments

Chronic disruption of circadian rhythms by night shift work is associated with an increased breast cancer risk. However, little is known about the impact of night shift on peripheral circadian genes (CGs) and circadian-controlled genes (CCGs) associated with breast cancer. Hence, we assessed central clock markers (melatonin and cortisol) in plasma, and peripheral CGs (PER1, PER2, PER3, and BMAL1) and CCGs (ESR1 and ESR2) in peripheral blood mononuclear cells (PBMCs). In day shift nurses (n = 12), 24-h rhythms of cortisol and melatonin were aligned with day shift-oriented light/dark schedules. The mRNA expression of PER2, PER3, BMAL1, and ESR2 showed 24-h rhythms with peak values in the morning. In contrast, night shift nurses (n = 10) lost 24-h rhythmicity of cortisol with a suppressed morning surge but retained normal rhythmic patterns of melatonin, leading to misalignment between cortisol and melatonin. Moreover, night shift nurses showed disruption of rhythmic expressions of PER2, PER3, BMAL1, and ESR2 genes, resulting in an impaired inverse correlation between PER2 and BMAL1 compared to day shift nurses. The observed trends of disrupted circadian markers were recapitulated in additional day (n = 20) and night (n = 19) shift nurses by measurement at early night and midnight time points. Taken together, this study demonstrated the misalignment of cortisol and melatonin, associated disruption of PER2 and ESR2 circadian expressions, and internal misalignment in peripheral circadian network in night shift nurses. Morning plasma cortisol and PER2, BMAL1, and ESR2 expressions in PBMCs may therefore be useful biomarkers of circadian disruption in shift workers.

Circadian-independent light regulation of mammalian metabolism

The daily light-dark cycle is a key zeitgeber (time cue) for entraining an organism's biological clock, whereby light sensing by retinal photoreceptors, particularly intrinsically photosensitive retinal ganglion cells, stimulates the suprachiasmatic nucleus of the hypothalamus, a central pacemaker that in turn orchestrates the rhythm of peripheral metabolic activities. Non-rhythmic effects of light on metabolism have also been long known, and their transduction mechanisms are only beginning to unfold. Here, we summarize emerging evidence that, in mammals, light exposure or deprivation profoundly affects glucose homeostasis, thermogenesis and other metabolic activities in a clock-independent manner. Such light regulation could involve melanopsin-based, intrinsically photosensitive retinal ganglion cell-initiated brain circuits via the suprachiasmatic nucleus of the hypothalamus and other nuclei, or direct stimulation of opsins expressed in the hypothalamus, adipose tissue, blood vessels and skin to regulate sympathetic tone, lipolysis, glucose uptake, mitochondrial activation, thermogenesis, food intake, blood pressure and melanogenesis. These photic signalling events may coordinate with circadian-based mechanisms to maintain metabolic homeostasis, with dysregulation of this system underlying metabolic diseases caused by aberrant light exposure, such as environmental night light and shift work.

The environment and the internal clocks: The study of their relationships from prehistoric to modern times

The origin of biological rhythms goes back to the very beginning of life. They are observed in the animal and plant world at all levels of organization, from cells to ecosystems. As early as the 18th century, plant scientists were the first to explain the relationship between flowering cycles and environmental cycles, emphasizing the importance of daily light-dark cycles and the seasons. Our temporal structure is controlled by external and internal rhythmic signals. Light is the main synchronizer of the circadian system, as daily exposure to light entrains our clock over 24 hours, the endogenous period of the circadian system being close to, but not exactly, 24 hours. In 1960, a seminal scientific meeting, the Cold Spring Harbor Symposium on Biological Rhythms, brought together all the biological rhythms scientists of the time, a number of whom are considered the founders of modern chronobiology. All aspects of biological rhythms were addressed, from the properties of circadian rhythms to their practical and ecological aspects. Birth of chronobiology dates from this period, with the definition of its vocabulary and specificities in metabolism, photoperiodism, animal physiology, etc. At around the same time, and right up to the present day, research has focused on melatonin, the circadian neurohormone of the pineal gland, with data on its pattern, metabolism, control by light and clinical applications. However, light has a double face, as it has positive effects as a circadian clock entraining agent, but also deleterious effects, as it can lead to chronodisruption when exposed chronically at night, which can increase the risk of cancer and other diseases. Finally, research over the past few decades has unraveled the anatomical location of circadian clocks and their cellular and molecular mechanisms. This recent research has in turn allowed us to explain how circadian rhythms control physiology and health.

Time of day and circadian disruption influence host response and parasite growth in a mouse model of cerebral malaria

Malaria is a disease caused by infection with parasite Plasmodium spp. We studied the circadian regulation of host responses to the parasite, in a mouse model of cerebral malaria. The course of the disease was markedly affected by time of infection, with decreased parasitemia and increased inflammation upon infection in the middle of the night. At this time, there were fewer reticulocytes, which are target cells of the parasites. We next investigated the effects of desynchronization of host clocks on the infection: after 10 weeks of recurrent jet lags, mice showed decreased parasite growth and lack of parasite load rhythmicity, paralleled by a loss of glucose rhythm. Accordingly, disrupting host metabolic rhythms impacted parasite load rhythmicity. In summary, our findings of a circadian modulation of malaria parasite growth and infection shed light on aspects of the disease relevant to human malaria and could contribute to new therapeutic or prophylactic measures.

Molecular-Level Dysregulation of Insulin Pathways and Inflammatory Processes in Peripheral Blood Mononuclear Cells by Circadian Misalignment

Circadian misalignment due to night work has been associated with an elevated risk for chronic diseases. We investigated the effects of circadian misalignment using shotgun protein profiling of peripheral blood mononuclear cells taken from healthy humans during a constant routine protocol, which was conducted immediately after participants had been subjected to a 3-day simulated night shift schedule or a 3-day simulated day shift schedule. By comparing proteomic profiles between the simulated shift conditions, we identified proteins and pathways that are associated with the effects of circadian misalignment and observed that insulin regulation pathways and inflammation-related proteins displayed markedly different temporal patterns after simulated night shift. Further, by integrating the proteomic profiles with previously assessed metabolomic profiles in a network-based approach, we found key associations between circadian dysregulation of protein-level pathways and metabolites of interest in the context of chronic metabolic diseases. Endogenous circadian rhythms in circulating glucose and insulin differed between the simulated shift conditions. Overall, our results suggest that circadian misalignment is associated with a tug of war between central clock mechanisms controlling insulin secretion and peripheral clock mechanisms regulating insulin sensitivity, which may lead to adverse long-term outcomes such as diabetes and obesity. Our study provides a molecular-level mechanism linking circadian misalignment and adverse long-term health consequences of night work.

Strategies that nurses working irregular night shifts use to improve sleep quality: A qualitative study among good and poor sleepers

AIMS

To assess the sleep strategies that nurses working irregular night shifts use to improve their sleep quality, and to compare the strategies of good and poor sleepers to determine whether the differences between the two groups could provide insights into possible effective strategies.

DESIGN

A qualitative descriptive study.

METHODS

The study was conducted from September 2019 to January 2020. Thirty-four nurses working irregular night shifts participated; 17 were classified as good sleepers and 17 as poor sleepers based on the Sleep-Wake Experience List, a validated self-report instrument that measures one's sleep quality. Interviews were conducted using open questions to explore strategies around the night-shift set. The interviews were analysed using thematic analysis.

FINDINGS

Both groups described similar and different strategies that help them work and sleep well during and after night shifts. However, good sleepers mentioned a greater number of strategies and seemed to have thought about them more than poor sleepers. The most common strategies were having a clear structure, being organized-especially regarding sleeping time-maintaining a daily routine and adjusting their sleep environment.

CONCLUSION

Healthcare institutions should consider offering education and training programs aimed at empowering nurses who work irregular night shifts. These programs should provide nurses with various sleep strategies to enhance their sleep quality and overall well-being.

IMPLICATIONS FOR THE PROFESSION

Nurses working irregular night shifts can possibly enhance their sleep quality by making personalized plans, for example, including a clear day structure, or an optimized sleep environment.

IMPACT

The study focused on how nurses working night shifts could possibly enhance their sleep quality. The findings highlight the importance of providing nurses with diverse sleep strategies to improve sleep quality, helping them to identify what works best for them and consistently apply these strategies.

REPORTING METHOD

The Consolidated Criteria for Reporting Qualitative Research guidelines were followed.

PATIENT OR PUBLIC CONTRIBUTION

Nurses working irregular night shifts at Maastricht University Medical Center in Maastricht, the Netherlands, who agreed to participate in the study, engaged in a discussion to assess the relevance of sleep quality to their work. They were also encouraged to share their perspectives during the interviews.

Circadian rhythm regulates the function of immune cells and participates in the development of tumors

Circadian rhythms are present in almost all cells and play a crucial role in regulating various biological processes. Maintaining a stable circadian rhythm is essential for overall health. Disruption of this rhythm can alter the expression of clock genes and cancer-related genes, and affect many metabolic pathways and factors, thereby affecting the function of the immune system and contributing to the occurrence and progression of tumors. This paper aims to elucidate the regulatory effects of BMAL1, clock and other clock genes on immune cells, and reveal the molecular mechanism of circadian rhythm's involvement in tumor and its microenvironment regulation. A deeper understanding of circadian rhythms has the potential to provide new strategies for the treatment of cancer and other immune-related diseases.

The association between night shift work and osteoporosis risk in adults: A cross-sectional analysis using NHANES

Purpose

Through this study, we assess whether night shift work increases the risk of osteoporosis, and explore the effects of age, gender, or lifestyle differences.

Methods

This cross-sectional study included the collection of data from a sample of the US adults who participated in the National Health and Nutrition Examination Survey (NHANES) over a 7.3-year period (2007-2008, 2009-2010, 2017-March2020), including 4408 participants (2351[52.8%] men and 2057[47.2%] women), with an age range of 20-80 years. The primary variables, health status, nutrition, harmful lifestyle habits, and bone mineral density (BMD), were segregated, and analyzed according to different work schedules. Linear regression models were conducted to evaluate correlations of night shift work and T-scores. Associations between night shift work and osteoporosis were examined using logistic regression analyses. All regression models were stratified by gender and age ≥50 years. Osteoporosis was defined as BMD at the femoral neck or total spine equal to or less than 2.5 standard deviations below the mean for youthful people of the same gender. All data were obtained using questionnaires and examinations collected in mobile examination center (MEC) from NHANES.

Results

After multivariate adjustment, night shift work was related to statistically significant decreases of the total spine in T-scores of females aged ≥50 years. Furthermore, night shift work of the overall population (OR = 2.31 [95% CI, 1.03-5.18]; P = 0.043) and females aged ≥50 years (OR = 4.6 [95% CI, 1.21-17.54]; P = 0.025) was related to an increased prevalence of osteoporosis.

Conclusion

Night shift work correlates with a higher risk of osteoporosis in the population of the US adults, with the combined effect of age, gender, and harmful lifestyle.

Extensive dynamic changes in the human transcriptome and its circadian organization during prolonged bed rest

Physiological and molecular processes including the transcriptome change across the 24-h day, driven by molecular circadian clocks and behavioral and systemic factors. It is not known how the temporal organization of the human transcriptome responds to a long-lasting challenge. This may, however, provide insights into adaptation, disease, and recovery. We investigated the human 24-h time series transcriptome in 20 individuals during a 90-day constant bed rest protocol. We show that the protocol affected 91% of the transcriptome with 76% of the transcriptome still affected after 10 days of recovery. Dimensionality-reduction approaches revealed that many affected transcripts were associated with mRNA translation and immune function. The number, amplitude, and phase of rhythmic transcripts, including clock genes, varied significantly across the challenge. These findings of long-lasting changes in the temporal organization of the transcriptome have implications for understanding the mechanisms underlying health consequences of conditions such as microgravity and bed rest.

Association between night work and prostate cancer: a systematic review and meta-analysis

OBJECTIVE

The aim was to conduct a systematic review and meta-analysis to study the association between night work and the development of prostate cancer.

METHODS

A systematic literature search was conducted in CINAHL, Embase, MEDLINE, and Web of Science. Studies were included based on a PECOS; the population included men in/above the working age, exposure defined as night work, outcome defined as prostate cancer, and study design restricted to cohort studies. The exclusion of articles, risk-of-bias assessment, and data extraction were performed by two reviewers. A meta-analysis was conducted using a random-effects model, including a sensitivity analysis stratified based on the risk-of-bias assessment. We evaluated publication bias using a funnel plot and Egger´s test, and the level of evidence was assessed using GRADE.

RESULTS

A total of 528 articles were identified, and eight cohort studies were included. Three studies had a moderate risk of bias, while five studies had a high risk of bias. The meta-analysis showed a pooled hazard ratio (HR) of 1.0 (95% CI 0.6-1.7). In the sensitivity analysis, moderate vs. high risk-of-bias studies showed a pooled HR of 1.2 (95% CI 0.3-4.1) and 0.9 (95% CI 0.6-1.3), respectively. Based on GRADE, the level of evidence was rated low.

CONCLUSION

We found no association between night work and the development of prostate cancer. The evidence was assessed as limited and inconsistent. Future studies encompassing consistent definitions of night work, including objective exposure data, are highly warranted.

Brain structural correlates of subjective sleepiness and insomnia symptoms in shift workers

Background

Studies on the brain structures of shift workers are limited; thus, this cross-sectional study aimed to compare the brain structures and the brain structural correlates of subjective sleepiness and insomnia symptoms between shift workers and non-shift workers.

Methods

Shift workers (n = 63) and non-shift workers (n = 58) completed questionnaires assessing subjective sleepiness and insomnia symptoms. Cortical thickness, cortical surface area, and subcortical volumes were measured by magnetic resonance imaging. The brain morphometric measures were compared between the groups, and interaction analyses using the brain morphometric measures as the dependent variable were performed to test the interactions between the study group and measures of sleep disturbance (i.e., subjective sleepiness and insomnia symptoms).

Results

No differences in cortical thickness, cortical surface area, or subcortical volumes were detected between shift workers and non-shift workers. A single cluster in the left motor cortex showed a significant interaction between the study group and subjective sleepiness in the cortical surface area. The correlation between the left motor cortex surface area and the subjective sleepiness level was negative in shift workers and positive in non-shift workers. Significant interaction between the study group and insomnia symptoms was present for the left/right putamen volumes. The correlation between the left/right putamen volumes and insomnia symptom levels was positive in shift workers and negative in non-shift workers.

Conclusion

Left motor cortex surface area and bilateral putamen volumes were unique structural correlates of subjective sleepiness and insomnia symptoms in shift workers, respectively.

Interindividual variability in coherence between self-reported alertness and performance in shift workers

OBJECTIVES

Evidence indicates that self-reported measures of alertness do not always reflect performance impairments. The present study aims to explore whether subjective and objective measures of vigilance vary in the same direction in individuals working nights.

METHODS

A total of 76 police officers participated to a month-long observational study. They worked either a 2 or 3-shift system during which they self-reported alertness and completed a psychomotor vigilance task several times a day.

RESULTS

A reduction in alertness and reaction speed was observed with time awake. At the group level, changes in alertness and reaction speed with time awake were positively correlated during night shifts only. In 63.6% of the officers, changes were coherent between both variables. The other officers reported that their alertness dropped (25.5%) or improved (10.9%) whereas their performance changed in the opposite direction.

CONCLUSION

Significant interindividual variability exists in self-appraisal vigilance impairment due to night shift work.

Unraveling the interplay of circadian rhythm and sleep deprivation on mood: A Real-World Study on first-year physicians

The interplay between circadian rhythms, time awake, and mood remains poorly understood in the real-world. Individuals in high-stress occupations with irregular schedules or nighttime shifts are particularly vulnerable to depression and other mood disorders. Advances in wearable technology have provided the opportunity to study these interactions outside of a controlled laboratory environment. Here, we examine the effects of circadian rhythms and time awake on mood in first-year physicians using wearables. Continuous heart rate, step count, sleep data, and daily mood scores were collected from 2,602 medical interns across 168,311 days of Fitbit data. Circadian time and time awake were extracted from minute-by-minute wearable heart rate and motion measurements. Linear mixed modeling determined the relationship between mood, circadian rhythm, and time awake. In this cohort, mood was modulated by circadian timekeeping (p<0.001). Furthermore, we show that increasing time awake both deteriorates mood (p<0.001) and amplifies mood's circadian rhythm nonlinearly. These findings demonstrate the contributions of both circadian rhythms and sleep deprivation to underlying mood and show how these factors can be studied in real-world settings using Fitbits. They underscore the promising opportunity to harness wearables in deploying chronotherapies for psychiatric illness.

Circadian Disruption in Night Shift Work and Its Association with Chronic Pulmonary Diseases

Globalization and the expansion of essential services over continuous 24 h cycles have necessitated the adaptation of the human workforce to shift-based schedules. Night shift work (NSW) causes a state of desynchrony between the internal circadian machinery and external environmental cues, which can impact inflammatory and metabolic pathways. The discovery of clock genes in the lung has shed light on potential mechanisms of circadian misalignment in chronic pulmonary disease. Here, the current knowledge of circadian clock disruption caused by NSW and its impact on lung inflammation and associated pathophysiology in chronic lung diseases, such as asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, and COVID-19, is reviewed. Furthermore, the limitations of the current understanding of circadian disruption and potential future chronotherapeutic advances are discussed.

The Associations of Chronotype and Shift Work With Rheumatoid Arthritis

The circadian clock regulates multiple aspects of human physiology including immunity. People have a circadian preference termed chronotype. Those with an evening preference may be better suited to shift work, but also carry higher risk of adverse health. Shift work leads to misalignment of circadian rhythms and is associated with increased risk of inflammatory disease such as asthma and cancer. Here, we investigate the association between chronotype, shift work, and rheumatoid arthritis (RA). The associations between exposures of shift work and chronotype on risk of RA were studied in up to 444,210 U.K. Biobank participants. Multivariable logistic regression models were adjusted for covariates: age, sex, ethnicity, alcohol intake, smoking history, Townsend Deprivation Index (TDI), sleep duration, length of working week, and body mass index (BMI). After adjusting for covariates, individuals with a morning chronotype had lower odds of having rheumatoid arthritis (RA; odds ratio [OR]: 0.93, 95% confidence interval [CI]: 0.88-0.99) when compared to intermediate chronotypes. The association between morning chronotype and RA persisted with a more stringent RA case definition (covariate-adjusted OR: 0.89, 95% CI: 0.81-0.97). When adjusted for age, sex, ethnicity, and TDI, shift workers had higher odds of RA (OR: 1.22, 95% CI: 1.1-1.36) compared to day workers that attenuated to the null after further covariate adjustment (OR: 1.1, 95% CI: 0.98-1.22). Morning chronotypes working permanent night shifts had significantly higher odds of RA compared to day workers (OR: 1.89, 95% CI: 1.19-2.99). These data point to a role for circadian rhythms in RA pathogenesis. Further studies are required to determine the mechanisms underlying this association and understand the potential impact of shift work on chronic inflammatory disease and its mediating factors.

The Effects of Shift Work on the Immune System: A Narrative Review

Working a shift work schedule has been hypothesized to have negative effects on health. One such described consequence is altered immune response and increased risk of infections. Former reviews have concluded that more knowledge is needed to determine how shift work affects the immune system. Since the last review focusing on this subject was published in 2016, new insight has emerged. We performed a search of the topic in PubMed, Scopus and Embase, identifying papers published after 2016, finding a total of 13 new studies. The articles identified showed inconsistent effect on immune cells, cytokines, circadian rhythms, self-reported infections, and vaccine response as a result of working a shift schedule. Current evidence suggests working shifts influence the immune system, however the clinical relevance and the mechanism behind this potential association remains elusive. Further studies need to include longitudinal design and objective measures of shift work and immune response.

The impact of shift-work light conditions on tissue-specific circadian rhythms of canonical clock genes: insights from a mouse model study

Background: The natural day-night cycle synchronizes our circadian rhythms, but modern work practices like night shifts disrupt this pattern, leading to increased exposure to nighttime light. This exposure is linked to various health issues. While some studies have explored the effects of night shifts on human circadian rhythms, there is limited research on the consequences of long-term exposure to shift-work light conditions. Rodents can provide valuable insights into these effects. This study aimed to examine how short- or long-term exposure to rotating shifts and chronic jetlag affects the core circadian oscillators in the liver and skin of mammals. Methods: C57BL/6J male mice were subjected to simulated shift-work light conditions, including short-term or long-term rotating shifts and chronic jet-lag conditions. Liver and skin samples were collected every four hours over a 24-hour period on the second day of constant darkness. RNA was extracted and qRT-PCR analysis was conducted to measure the circadian gene expression in liver and skin tissues. Circadian rhythm analysis using CircaCompare compared the control group to mice exposed to shift-work light conditions. Results: The liver's circadian clock is significantly altered in mice under long-term rotating shift conditions, with a lesser but still noticeable impact in mice experiencing chronic jetlag. However, short-term rotating shift conditions do not significantly affect the liver's circadian clock. Conversely, all three simulated shift conditions affect the skin's circadian clock, indicating that the skin clock is more sensitive to shift-work light conditions than the liver clock. Compared to the liver, the skin's circadian clock is greatly affected by long-term rotating shift conditions. Conclusions: The study findings indicate more pronounced disturbances in the canonical clock genes of the skin compared to the liver under simulated shift-work light conditions. These results suggest that the skin clock is more vulnerable to the effects of shift-work.

Potential effects of shift work on skin autoimmune diseases

Shift work is associated with systemic chronic inflammation, impaired host and tumor defense and dysregulated immune responses to harmless antigens such as allergens or auto-antigens. Thus, shift workers are at higher risk to develop a systemic autoimmune disease and circadian disruption with sleep impairment seem to be the key underlying mechanisms. Presumably, disturbances of the sleep-wake cycle also drive skin-specific autoimmune diseases, but epidemiological and experimental evidence so far is scarce. This review summarizes the effects of shift work, circadian misalignment, poor sleep, and the effect of potential hormonal mediators such as stress mediators or melatonin on skin barrier functions and on innate and adaptive skin immunity. Human studies as well as animal models were considered. We will also address advantages and potential pitfalls in animal models of shift work, and possible confounders that could drive skin autoimmune diseases in shift workers such as adverse lifestyle habits and psychosocial influences. Finally, we will outline feasible countermeasures that may reduce the risk of systemic and skin autoimmunity in shift workers, as well as treatment options and highlight outstanding questions that should be addressed in future studies.

The Effect of Night Shifts on 24-h Rhythms in the Urinary Metabolome of Police Officers on a Rotating Work Schedule

Shift workers face an increased risk of metabolic health problems, but the direct metabolic response to working nights is not fully understood. The aim of this study was to investigate the effect of night shifts on the 24-h urinary metabolome of shift workers. Eleven police officers working rotating shifts completed two 24-h laboratory visits that took place before and after they worked 7 consecutive nights. Sleep and meals were scheduled on a day schedule in the first visit and then on a night schedule (i.e., sleep and meals shifted by approximately 12 h) in the second visit. Targeted metabolomic analysis was performed on urine samples collected throughout these laboratory visits. Differential rhythmicity analysis was used to compare 24-h rhythms in urinary metabolites in both conditions. Our results show that on the day schedule, 24-h rhythms are present in the urinary levels of the majority of metabolites, but that this is significantly reduced on the night schedule, partly due to loss of organic acid rhythmicity. Furthermore, misalignment of 24-h metabolite rhythms with the shifted behavioral cycles in the night schedule was observed in more than half of the metabolites that were rhythmic in both conditions (all acylcarnitines). These results show that working nights alters the daily rhythms of the urinary metabolome in rotating shift workers, with the most notable impact observed for acylcarnitines and organic acids, 2 metabolite classes involved in mitochondrial function. Further research is warranted to study how these changes relate to the increased metabolic risks associated with shift work.

The role of insufficient sleep and circadian misalignment in obesity

Traditional risk factors for obesity and the metabolic syndrome, such as excess energy intake and lack of physical activity, cannot fully explain the high prevalence of these conditions. Insufficient sleep and circadian misalignment predispose individuals to poor metabolic health and promote weight gain and have received increased research attention in the past 10 years. Insufficient sleep is defined as sleeping less than recommended for health benefits, whereas circadian misalignment is defined as wakefulness and food intake occurring when the internal circadian system is promoting sleep. This Review discusses the impact of insufficient sleep and circadian misalignment in humans on appetite hormones (focusing on ghrelin, leptin and peptide-YY), energy expenditure, food intake and choice, and risk of obesity. Some potential strategies to reduce the adverse effects of sleep disruption on metabolic health are provided and future research priorities are highlighted. Millions of individuals worldwide do not obtain sufficient sleep for healthy metabolic functions. Furthermore, modern working patterns, lifestyles and technologies are often not conducive to adequate sleep at times when the internal physiological clock is promoting it (for example, late-night screen time, shift work and nocturnal social activities). Efforts are needed to highlight the importance of optimal sleep and circadian health in the maintenance of metabolic health and body weight regulation.

Autoimmune pre-disease

Approximately 5% of the world-wide population is affected by autoimmune diseases. Overall, autoimmune diseases are still difficult to treat, impose a high burden on patients, and have a significant economic impact. Like other complex diseases, e.g., cancer, autoimmune diseases develop over several years. Decisive steps in the development of autoimmune diseases are (i) the development of autoantigen-specific lymphocytes and (often) autoantibodies and (ii) potentially clinical disease manifestation at a later stage. However, not all healthy individuals with autoantibodies develop disease manifestations. Identifying autoantibody-positive healthy individuals and monitoring and inhibiting their switch to inflammatory autoimmune disease conditions are currently in their infancy. The switch from harmless to inflammatory autoantigen-specific T and B-cell and autoantibody responses seems to be the hallmark for the decisive factor in inflammatory autoimmune disease conditions. Accordingly, biomarkers allowing us to predict this progression would have a significant impact. Several factors, such as genetics and the environment, especially diet, smoking, exposure to pollutants, infections, stress, and shift work, might influence the progression from harmless to inflammatory autoimmune conditions. To inspire research directed at defining and ultimately targeting autoimmune predisease, here, we review published evidence underlying the progression from health to autoimmune predisease and ultimately to clinically manifest inflammatory autoimmune disease, addressing the following 3 questions: (i) what is the current status, (ii) what is missing, (iii) and what are the future perspectives for defining and modulating autoimmune predisease.

Sex Inclusion in Transcriptome Studies of Daily Rhythms

Biomedical research on mammals has traditionally neglected females, raising the concern that some scientific findings may generalize poorly to half the population. Although this lack of sex inclusion has been broadly documented, its extent within circadian genomics remains undescribed. To address this gap, we examined sex inclusion practices in a comprehensive collection of publicly available transcriptome studies on daily rhythms. Among 148 studies having samples from mammals in vivo, we found strong underrepresentation of females across organisms and tissues. Overall, only 23 of 123 studies in mice, 0 of 10 studies in rats, and 9 of 15 studies in humans included samples from females. In addition, studies having samples from both sexes tended to have more samples from males than from females. These trends appear to have changed little over time, including since 2016, when the US National Institutes of Health began requiring investigators to consider sex as a biological variable. Our findings highlight an opportunity to dramatically improve representation of females in circadian research and to explore sex differences in daily rhythms at the genome level.

Enhancing the metabolic benefits of exercise: Is timing the key?

Physical activity represents a potent, non-pharmacological intervention delaying the onset of over 40 chronic metabolic and cardiovascular diseases, including type 2 diabetes, coronary heart disease, and reducing all-cause mortality. Acute exercise improves glucose homeostasis, with regular participation in physical activity promoting long-term improvements in insulin sensitivity spanning healthy and disease population groups. At the skeletal muscle level, exercise promotes significant cellular reprogramming of metabolic pathways through the activation of mechano- and metabolic sensors, which coordinate downstream activation of transcription factors, augmenting target gene transcription associated with substrate metabolism and mitochondrial biogenesis. It is well established that frequency, intensity, duration, and modality of exercise play a critical role in the type and magnitude of adaptation; albeit, exercise is increasingly considered a vital lifestyle factor with a critical role in the entrainment of the biological clock. Recent research efforts revealed the time-of-day-dependent impact of exercise on metabolism, adaptation, performance, and subsequent health outcomes. The synchrony between external environmental and behavioural cues with internal molecular circadian clock activity is a crucial regulator of circadian homeostasis in physiology and metabolism, defining distinct metabolic and physiological responses to exercise unique to the time of day. Optimising exercise outcomes following when to exercise would be essential to establishing personalised exercise medicine depending on exercise objectives linked to disease states. We aim to provide an overview of the bimodal impact of exercise timing, i.e. the role of exercise as a time-giver (zeitgeber) to improve circadian clock alignment and the underpinning clock control of metabolism and the temporal impact of exercise timing on the metabolic and functional outcomes associated with exercise. We will propose research opportunities that may further our understanding of the metabolic rewiring induced by specific exercise timing.

Circadian Disruption and Consequences on Innate Immunity and Inflammatory Response

Circadian rhythms control almost all aspects of physiology and behavior, allowing temporal synchrony of these processes between each other, as well as with the external environment. In the immune system, daily rhythms of leukocyte functions can determine the strength of the immune response, thereby regulating the efficiency of defense mechanisms to cope with infections or tissue injury. The natural light/dark cycle is the prominent synchronizing agent perceived by the circadian clock, but this role of light is highly compromised by irregular working schedules and unintentional exposure to artificial light at night (ALAN). The primary concern is disrupted circadian control of important physiological processes, underlying potential links to adverse health effects. Here, we first discuss the immune consequences of genetic circadian disruption induced by mutation or deletion of specific clock genes. Next, we evaluate experimental research into the effects of disruptive light/dark regimes, particularly light-phase shifts, dim ALAN, and constant light on the innate immune mechanisms under steady state and acute inflammation, and in the pathogenesis of common lifestyle diseases. We suggest that a better understanding of the mechanisms by which circadian disruption influences immune status can be of importance in the search for strategies to minimize the negative consequences of chronodisruption on health.

Metabolic profiling of night shift work - The HORMONIT study

Mechanistic studies are needed to understand how rotating shift work perturbs metabolic processing. We collected plasma samples (n = 196) from 49 males, rotating car factory shift workers at the beginning and end of a night-shift (22:00-06:00 h) and day-shift (06:00 h-14:00 h). Samples underwent targeted LC-MS/MS metabolomics and concentrations of 130 metabolites were log2-transformed and pareto-scaled. An elastic net selected the most influential metabolites for linear mixed models examining within-person variation in metabolite levels at night-shift end (06:00 h) compared to day-shift start (06:00 h). Quantitative enrichment analysis explored differentially enriched biological pathways between sample time points. We included 20 metabolites (amino acids, biogenic amines, acylcarnitines, glycerophospholipids) in mixed models. Night-shift was associated with changes in concentrations of arginine (geometric mean ratio [GMR] 2.30, 95%CI 1.25, 4.23), glutamine (GMR 2.22, 95%CI 1.53, 3.24), kynurenine (GMR 3.22, 95%CI 1.05, 9.87), lysoPC18:2 (GMR 1.86, 95%CI 1.11, 3.11), lysoPC20:3 (GMR 2.48, 95%CI 1.05, 5.83), PCaa34:2 (GMR 2.27, 95%CI 1.16, 4.44), and PCae38:5 (GMR 1.66, 95%CI 1.02, 2.68). Tryptophan metabolism, glutathione metabolism, alanine metabolism, glycine and serine metabolism, and urea cycle were pathways differing between shifts. Night shift work was associated with changes in metabolites and the perturbation of metabolic and biochemical pathways related to a variety of health outcomes.

Immune disruptions and night shift work in hospital healthcare professionals: The intricate effects of social jet-lag and sleep debt

Objectives

We aimed to examine the effects of circadian and sleep rhythm disruptions on immune biomarkers among hospital healthcare professionals working night shifts and rotating day shifts.

Methods

Hospital nurses working either as permanent night shifters (n=95) or as day shifters rotating between morning and afternoon shifts (n=96) kept a daily diary on their sleep and work schedules over a full working week. Blood samples were collected at the beginning and end of the last shift during the week, and participants were categorized into three groups based on work shift: morning shift (39 day shifters sampled at 7:00 and 14:00), afternoon shift (57 day shifters sampled at 14:00 and 21:00), and night shift (95 night shifters sampled at 21:00 and 7:00). Circulating blood counts in immune cells, interleukin-6 and C-reactive protein concentrations as well as total sleep time per 24 hours during work days (TST24w) and free days (TST24f), sleep debt (TST24f - TST24w) and social jet-lag (a behavioral proxy of circadian misalignment) were assessed.

Results

Compared with day shifters, night shifters had shorter sleep duration (TST24w=5.4 ± 1.4h), greater sleep debt (3.2 ± 1.4 h) and social jet-lag (6.7 ± 2.4 h). Variations of immune biomarkers concentrations were consistent with the expected diurnal variations among day shifters (i.e., low level in the morning, increase during the day, peak value in the evening). By contrast, in night shifters, blood concentrations of total lymphocytes, T-helper cells, cytotoxic T-cells, memory B-cells and interleukin-6 were lower at 21:00, increased during the night, and reached higher values at 7:00. Multivariate analyses ruled out significant impact of TST24w, sleep debt, and social jet-lag on immune biomarkers concentrations among day shifters. In contrast, among night shifters, multivariate analyses indicated a combined effect of total sleep time (TST24w), sleep debt and social jet-lag for total lymphocytes and T-helper cells but only a social jet-lag effect for interleukin-6 and a single total sleep time effect for neutrophil and B-Cells.

Conclusions

Altogether, our results point to intricate response patterns of immune rhythms to circadian misalignment and sleep debt in night shifters. Specifically, these altered pattern expressions of immune cells may increase vulnerability to infections and reduce vaccination efficiency in night workers.

Disruption of cellular immune response among male rotating night shift workers in Spain– The HORMONIT study

Introduction

Preliminary studies suggest that night shift work is associated with a desynchronization of rhythmic immune markers, possibly explaining the increased risk of infection, cardiometabolic disorders, and cancer in shift workers.

Methods

This study included 51 male rotating shift workers from a car industry in Barcelona, Spain, sampled twice toward the end of a 3-week night shift (22:00-06:00 h) and a 3-week day shift (06:00-14:00 h) rotation. We collected four blood samples per worker, at the start and end of each shift. We measured 27 cytokines, chemokines and growth factors in plasma samples by luminex using the Cytokine Human Magnetic 30-Plex Panel LHC6003M and applied linear mixed models to examine within-person associations between shift work and analytes’ concentrations, comparing samples taken at 06:00 h on a day and night shift. We also conducted a factor analysis using analyte concentrations from all 4 time points for each individual to identify common factors and determine if these factors were altered by shift work.

Results

We observed lower levels of 15 analytes in the night shift compared to the day shift including cytokines (pro-inflammatory TNF-α, IL-2R; anti-inflammatory IL1-RA; Th1 IL-2, Th2 IL-4 and Th17 Il-17), chemokines (IP-10, MIP-1α, MIP-1β, RANTES) and growth factors (EGF, G-CSF, HGF, VEGF, FGF). In a factor analysis, three factors were identified. The main factor (Factor 1), explaining 57% of the variance and including IL-1β, IL-12, IL-15, MIP-1α, MIP-1β, EGF and FGF; and another factor (Factor 3) explaining 10% of the variance and including the Th1 cytokine IL-12, were inversely associated with the night shift (coefficient: -0.17, 95%CI -0.32 to -0.01 and coefficient: -0.22, 95%CI -0.38, -0.06, for Factors 1 and 3, respectively). Our results indicate that night shift disrupts the levels of several immune markers, which could contribute to the increased risk of infections and cancer reported in night shift workers.

Conclusion

Night shift is associated with disruption of multiple immune response pathways.

Does knowledge of sleep hygiene recommendations match behaviour in Australian shift workers? A cross-sectional study

OBJECTIVES

Shiftworkers routinely obtain inadequate sleep, which has major health consequences. Sleep hygiene describes a range of behaviours, lifestyle and environmental factors that can improve sleep. To date, limited research has examined sleep hygiene in shiftworkers. This study aimed to assess the sociodemographic and behavioural correlates of sleep hygiene knowledge and engagement with sleep hygiene practices in Australian shiftworkers.

STUDY DESIGN

An online, cross-sectional survey.

SETTING AND PARTICIPANTS

Australian adults from across multiple industries (n=588) who work shift work.

MEASURES

The online survey included questions regarding sleep hygiene knowledge and questions from modified versions of the Pittsburgh Sleep Quality Index and Sleep Hygiene Index.

RESULTS

Of the 588 participants, 52.9% reported having heard of 'sleep hygiene'. Of these participants, 77.5% reported understanding the term moderately, extremely or very well. Engagement with each sleep hygiene practice was varied. Common sleep hygiene practices were controlling the bedroom environment (eg, a cool, dark and quiet bedroom). Less common practices were avoiding light as bedtime approaches. Logistic regressions revealed that shiftworkers who had heard of sleep hygiene were more likely to engage in sleep hygiene practices and had better sleep quality compared with those who had not heard of sleep hygiene. Increased engagement in sleep hygiene practices did not predict the likelihood of individuals reporting better sleep quality.

CONCLUSIONS

Shiftworkers demonstrated varied knowledge, understanding and engagement with individual sleep hygiene practices. Future research should focus on the development of sleep hygiene interventions that accommodate the unique challenges of shift work to optimise sleep.

Work Exposures and Development of Cardiovascular Diseases: A Systematic Review

INTRODUCTION

Cardiovascular diseases (CVDs) are the number one cause of death, and there is evidence that work exposures could be associated with their development. This study aimed to systematically review observational studies of adults exposed to job strain, effort-reward imbalance, long working hours, job insecurity, shift work, and occupational noise, and assess the association of those work exposures with CVDs.

METHODS

The Navigation Guide framework was applied. The population were adults of working age (18-65), and cohort and case-control studies were included. The work exposures were job strain, effort-reward imbalance, long working hours, job insecurity, shift work, and occupational noise. The outcomes were cerebrovascular diseases, ischaemic heart disease, and hypertensive diseases. The selection, data extraction, risk of bias assessment, and quality assessment were carried out by two reviewers independently and disagreements were solved by a third reviewer or by consensus. The synthesis of the results was done by applying the 'vote counting based on direction' method, and the results were summarized in an effect direction plot. The strength of the evidence for every risk factor and CVD was defined by consensus.

RESULTS

A total of 17 643 papers were initially identified in the literature search, but after applying the filters by title and abstract, and full text, 86 studies were finally included. From the included studies, sufficient evidence was found of the harmfulness of job strain for cerebrovascular disease and ischemic heart disease. Furthermore, there was sufficient evidence of the harmfulness of shift work for ischemic heart disease. Evidence of no relationship was found between long working hours and shift work with ischaemic heart disease and hypertensive disease, respectively. The other associations of work exposures and CVDs had limited or inadequate evidence of harmfulness.

CONCLUSIONS

In this comprehensive review, there was sufficient evidence of a harmful relationship between job strain, shift work, and CVDs. For the other work exposures, more high-quality studies are needed. In order to improve current prevention strategies for CVDs, the findings of this review imply that job strain and shift work are work exposures that constitute additional risk factors that could be approached as targets for worksite interventions.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42020179972.

Time-Related Eating Patterns Are Associated with the Total Daily Intake of Calories and Macronutrients in Day and Night Shift Workers

The aim of the study was to investigate whether time-related eating patterns are associated with the daily intake of calories and macronutrients in Brazilian male military police officers (n = 81; 29-day and 52-night workers; mean age: 36.4 ± 0.9 and 38.5 ± 0.7 years, respectively). Energy and macronutrient intake were determined by a non-consecutive 3-day food recall. Time-related eating patterns, such as the time of the first and the last meals, eating duration, and caloric midpoint, were evaluated. Individuals were classified as “early” or “late” eaters according to the median caloric midpoint. Night shift workers showed a later eating time for the last meal (p < 0.001), longer eating duration (p < 0.001), and later caloric midpoint (p = 0.037) than day workers. Late eaters from both workgroups consumed more 24 h energy (p = 0.028), fat in calories (p = 0.006) and protein (calories: p < 0.001; percentage of total calories: p = 0.042), and less carbohydrates in calories (p = 0.010) intake than early eaters. The time of the first meal was negatively correlated with 24 h energy (p = 0.024) and carbohydrate (p = 0.031) intake only in day workers. The time of the last meal was positively correlated with 24 h energy (day workers: β = 0.352; p = 0.044; night workers: β = 0.424; p = 0.002) and protein (day workers: β = 0.451; p = 0.013; night workers: β = 0.536; p < 0.001) intake for both shift workers, and with carbohydrate (β = 0.346; p = 0.016) and fat (β = 0.286; p = 0.042) intake only in night workers. Eating duration was positively correlated with energy (day workers: β = 0.473; p = 0.004; night workers: β = 0.320; p = 0.023) and carbohydrate (day workers: β = 0.418; p = 0.011; night workers: β = 0.364; p = 0.010) intake in both groups. Thus, time-related eating patterns indicative of intake later at night are associated with increased daily energy and macronutrient intake.

Sleep and vaccine administration time as factors influencing vaccine immunogenicity

The immunogenicity of vaccines is affected by host, external, environmental, and vaccine factors; in addition, sleep or circadian rhythms may also have effects. With the use of vaccines to mitigate the coronavirus disease 2019 (COVID-19) pandemic, research is underway to clarify what time of the day is optimal for COVID-19 vaccination and how disturbances of circadian rhythms will affect the immunogenicity of the vaccine in shift workers. Studies on the relationship between sleep time and the immunogenicity of vaccines for influenza and hepatitis have demonstrated that less sleep time and sleep deprivation tended to adversely affect immunogenicity. In some studies, there were even sex differences in these effects. When comparing shift workers with disturbances in their circadian rhythms and those who only worked during the day, one study found less antibody formation in shift workers; however, further studies on the relationship between shift work and the immunogenicity of vaccines are needed. Studies on the relationship between vaccine administration time and immunogenicity have shown different results according to age and sex. Therefore, future studies on vaccine administration time and immunogenicity may require an individualized approach for each vaccine and each population to be vaccinated. There is accumulating evidence on the effects of sleep and vaccine administration time on the immunogenicity of vaccines. However, further studies are needed to determine whether the association between immunogenicity and circadian rhythms and vaccine administration time can be used as a basis to increase the immunogenicity for individual vaccines.

The neurophysiologic basis of the human sleep–wake cycle and the physiopathology of the circadian clock: a narrative review

The objectives of this review were to explain the neurologic processes that control the human sleep–wake cycle as well as the pathophysiology of the human circadian clock. Non-rapid eye movement and rapid eye movement sleep are the two main phases of sleep. When triggered by circadian input from the anterior hypothalamus and sleep–wake homeostatic information from endogenous chemical signals (example, adenosine), the ventrolateral preoptic nucleus initiates the onset of sleep. Arousal in which there is a conscious monitoring of the surroundings and the ability to respond to external stimuli is known as wakefulness. It contrasts the state of sleep, in which receptivity to external stimuli is reduced. The higher the synchronous firing rates of cerebral cortex neurons, the longer the brain has been awake. Sleep–wake disturbances induced by endogenous circadian system disruptions or desynchronization between internal and external sleep–wake cycles are known as circadian rhythm sleep–wake disorder (CRSWD). Patients with CRSWD usually report chronic daytime drowsiness and/or insomnia, which interferes with their activities. CRSWD is diagnosed based on the results of some functional evaluations, which include measuring the circadian phase using core body temperature, melatonin secretion timing, sleep diaries, actigraphy, and subjective experiences (example, using the Morningness–Eveningness Questionnaire). CRSWD is classified as a dyssomnia in the second edition of the International Classification of Sleep Disorders, with six subtypes: advanced sleep phase, delayed sleep phase, irregular sleep–wake, free running, jet lag, and shift work types. CRSWD can be temporary (due to jet lag, shift work, or illness) or chronic (due to delayed sleep–wake phase disorder, advanced sleep–wake phase disorder, non-24-h sleep–wake disorder, or irregular sleep–wake rhythm disorder). The inability to fall asleep and wake up at the desired time is a common symptom of all CRSWDs.

Circadian disruption and cisplatin chronotherapy for mammary carcinoma

Solid tumors are commonly treated with cisplatin, which can cause off-target side effects in cancer patients. Chronotherapy is a potential strategy to reduce drug toxicity. To determine the effectiveness of timed-cisplatin treatment in mammals, we compared two conditions: clock disrupted jet-lag and control conditions. Under normal and disrupted clock conditions, triple-negative mammary carcinoma cells were injected subcutaneously into eight-week-old NOD.Cg-Prkdc^scid/J female mice. Tumor volumes and body weights were measured in these mice before and after treatment with cisplatin. We observed an increase in tumor volumes in mice housed under disrupted clock compared to the normal clock conditions. After treatment with cisplatin, we observed a reduced tumor growth rate in mice treated at ZT10 compared to ZT22 and untreated cohorts under normal clock conditions. However, these changes were not seen with the jet-lag protocol. We also observed greater body weight loss in mice treated with ZT10 compared to ZT22 or untreated mice in the jet-lag protocol. Our observations suggest that the effectiveness of cisplatin in mammary carcinoma treatment is time-dependent in the presence of the circadian clock.

The contribution of sleep to the neuroendocrine regulation of rhythms in human leukocyte traffic

Twenty-four-hour rhythms in immune parameters and functions are robustly observed phenomena in biomedicine. Here, we summarize the important role of sleep and associated parameters on the neuroendocrine regulation of rhythmic immune cell traffic to different compartments, with a focus on human leukocyte subsets. Blood counts of "stress leukocytes" such as neutrophils, natural killer cells, and highly differentiated cytotoxic T cells present a rhythm with a daytime peak. It is mediated by morning increases in epinephrine, leading to a mobilization of these cells out of the marginal pool into the circulation following a fast, beta2-adrenoceptor-dependent inhibition of adhesive integrin signaling. In contrast, other subsets such as eosinophils and less differentiated T cells are redirected out of the circulation during daytime. This is mediated by stimulation of the glucocorticoid receptor following morning increases in cortisol, which promotes CXCR4-driven leukocyte traffic, presumably to the bone marrow. Hence, these cells show highest numbers in blood at night when cortisol levels are lowest. Sleep adds to these rhythms by actively suppressing epinephrine and cortisol levels. In addition, sleep increases levels of immunosupportive mediators, such as aldosterone and growth hormone, which are assumed to promote T-cell homing to lymph nodes, thus facilitating the initiation of adaptive immune responses during sleep. Taken together, sleep-wake behavior with its unique neuroendocrine changes regulates human leukocyte traffic with overall immunosupportive effects during nocturnal sleep. In contrast, integrin de-activation and redistribution of certain leukocytes to the bone marrow during daytime activity presumably serves immune regulation and homeostasis.

Disruption of the circadian rhythms and its relationship with pediatric obesity

The circadian clock system is an evolutionarily conserved system by which organisms adapt their metabolic activities to environmental inputs, including nutrient availability. The disruption of this system has been pathogenically linked to the disintegration of metabolic homeostasis, leading to the development of metabolic complications, including obesity. Lifestyle factors that disrupt this system have been found to be associated with the development of metabolic disorder, which is most evidenced by the finding that shift workers are at an increased risk of developing various disorders, such as obesity and obesity-related complications. Lifestyle factors that contribute to a misalignment between the internal clock system and environmental rhythms have also been identified in children. A short sleep duration and skipping breakfast are prevalent in children and there is mounting evidence that these factors are associated with an increased risk of pediatric obesity; however, the underlying mechanisms have not yet been elucidated in detail. Our current understanding of the impact of lifestyle factors that cause a misalignment between the internal clock system and environmental rhythms on the development of pediatric obesity is summarized herein, with a discussion of potential mechanistic factors.

Disturbance of the Circadian System in Shift Work and Its Health Impact

The various non-standard schedules required of shift workers force abrupt changes in the timing of sleep and light-dark exposure. These changes result in disturbances of the endogenous circadian system and its misalignment with the environment. Simulated night-shift experiments and field-based studies with shift workers both indicate that the circadian system is resistant to adaptation from a day- to a night-oriented schedule, as determined by a lack of substantial phase shifts over multiple days in centrally controlled rhythms, such as those of melatonin and cortisol. There is evidence that disruption of the circadian system caused by night-shift work results not only in a misalignment between the circadian system and the external light-dark cycle, but also in a state of internal desynchronization between various levels of the circadian system. This is the case between rhythms controlled by the central circadian pacemaker and clock genes expression in tissues such as peripheral blood mononuclear cells, hair follicle cells, and oral mucosa cells. The disruptive effects of atypical work schedules extend beyond the expression profile of canonical circadian clock genes and affects other transcripts of the human genome. In general, after several days of living at night, most rhythmic transcripts in the human genome remain adjusted to a day-oriented schedule, with dampened group amplitudes. In contrast to circadian clock genes and rhythmic transcripts, metabolomics studies revealed that most metabolites shift by several hours when working nights, thus leading to their misalignment with the circadian system. Altogether, these circadian and sleep-wake disturbances emphasize the all-encompassing impact of night-shift work, and can contribute to the increased risk of various medical conditions. Here, we review the latest scientific evidence regarding the effects of atypical work schedules on the circadian system, sleep and alertness of shift-working populations, and discuss their potential clinical impacts.

Circadian Rhythm Effects on the Molecular Regulation of Physiological Systems

Nearly every system within the body contains an intrinsic cellular circadian clock. The circadian clock contributes to the regulation of a variety of homeostatic processes in mammals through the regulation of gene expression. Circadian disruption of physiological systems is associated with pathophysiological disorders. Here, we review the current understanding of the molecular mechanisms contributing to the known circadian rhythms in physiological function. This article focuses on what is known in humans, along with discoveries made with cell and rodent models. In particular, the impact of circadian clock components in metabolic, cardiovascular, endocrine, musculoskeletal, immune, and central nervous systems are discussed. © 2021 American Physiological Society. Compr Physiol 11:1-30, 2021.

Shift Work Predicts Increases in Lipopolysaccharide-Binding Protein, Interleukin-10, and Leukocyte Counts in a Cross-Sectional Study of Healthy Volunteers Carrying Low-Grade Systemic Inflammation

The disruption of inflammatory responses is a potential mechanism behind the harmful effects of shift work and is associated with increased risk of hypertension, stroke, obesity, diabetes, and cancer. These responses are linked to the proliferation of leukocytes in shift workers, suggesting a systemic signal as a potential mediator. The purpose of this study was to assess the relationship between systemic inflammation, leukocyte counts, and systemic endotoxemia in samples from a diverse cohort of day workers and shift workers. Participants (normothermic and normotensive) were healthy volunteers, non-smoking, and drug- and medication-free. The following outcomes were measured: C-reactive protein, TNF-α, IL-6, IL-1β, IL-10, leukocyte counts (monocytes, lymphocytes, and neutrophils), and lipopolysaccharide-binding protein (LBP). Risk factors that increase systemic inflammation, such as blood pressure, sleep loss, and cortisol, were also assessed. The results indicated that shift workers slept significantly less than day workers and had significantly increased concentrations of all of the cytokines measured as well as plasma cortisol. Regression models found that after controlling for covariates, shift-work exposure predicted the significant increase observed in IL-10, leukocyte counts, and LBP. Our results suggest that acute increases in low-grade systemic endotoxemia are unresolved during chronic shift-work exposure. This ongoing immune challenge may underlie the disrupted inflammatory responses characteristic of shift-work-related pathologies. Systemic endotoxemia may represent a novel target to investigate the early effects of exposure to shift-work schedules.

Chronodisruption by chronic jetlag impacts metabolic and gastrointestinal homeostasis in male mice

AIM

Chronodisruption desynchronizes peripheral clocks and leads to metabolic diseases. Feeding cues are important synchronizers of peripheral clocks and influence rhythmic oscillations in intestinal microbiota and their metabolites. We investigated whether chronic jetlag, mimicking frequent time zone travelling, affected the diurnal fluctuations in faecal short-chain fatty acid (SCFA) levels, that feed back to the gut clock to regulate rhythmicity in gut function.

METHODS

Rhythms in faecal SCFAs levels and in the expression of clock genes and epithelial markers were measured in the colonic mucosa of control and jetlagged mice. The entraining effect of SCFAs on the rhythm in clock gene mRNA expression was studied in primary colonic crypts. The role of the circadian clock in epithelial marker expression was studied in Arntl^-/- mice.

RESULTS

Chronic jetlag increased body weight gain and abolished the day/night food intake pattern which resulted in a phase-delay in the rhythm of faecal SCFAs that paralleled the shift in the expression of mucosal clock genes. This effect was mimicked by stimulation of primary colonic crypts from control mice with SCFAs. Jetlag abolished the rhythm in Tnfα, proglucagon and ghrelin expression but not in the expression of tight junction markers. Only a dampening in plasma glucagon-like peptide-1 but not in ghrelin levels was observed. Rhythms in ghrelin but not proglucagon mRNA expression were abolished in Arntl^-/- mice.

CONCLUSION

The altered food intake pattern during chronodisruption corresponds with the changes in rhythmicity of SCFA levels that entrain clock genes to affect rhythms in mRNA expression of gut epithelial markers.

New integrative approaches to discovery of pathophysiological mechanisms triggered by night shift work

Synchronization to periodic cues such as food/water availability and light/dark cycles is crucial for living organisms' homeostasis. Both factors have been heavily influenced by human activity, with artificial light at night (ALAN) being an evolutionary challenge imposed over roughly the last century. Evidence from studies in humans and animal models shows that overt circadian misalignment, such as that imposed to about 20% of the workforce by night shift work (NSW), negatively impinges on the internal temporal order of endocrinology, physiology, metabolism, and behavior. Moreover, NSW is often associated to mistimed feeding, with both unnatural behaviors being known to increase the risk of chronic diseases, such as eating disorders, overweight, obesity, cardiovascular, metabolic (particularly type 2 diabetes mellitus) and gastrointestinal disorders, some types of cancer, as well as mental disease including sleep disturbances, cognitive disorders, and depression. Regarding deleterious effects of ALAN on reproduction, increased risk of miscarriage, preterm delivery and low birth weight have been reported in shift-worker women. These mounting lines of evidence prompt further efforts to advance our understanding of the effects of long-term NSW on health. Emerging data suggest that NSW with or without mistimed feeding modify gene expression and functional readouts in different tissues/organs, which seem to translate into persistent cardiometabolic and endocrine dysfunction. However, this research avenue still faces multiple challenges, such as functional characterization of new experimental models more closely resembling human long-term NSW and mistimed feeding in males versus females; studying further target organs; identifying molecular changes by means of deep multi-omics analyses; and exploring biomarkers of NSW with translational medicine potential. Using high-throughput and systems biology is a relatively new approach to study NSW, aimed to generate experiments addressing new biological factors, pathways, and mechanisms, going beyond the boundaries of the circadian clock molecular machinery.

The circadian clock component BMAL1 regulates SARS-CoV-2 entry and replication in lung epithelial cells

The coronavirus disease 2019 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) coronavirus, is a global health issue with unprecedented challenges for public health. SARS-CoV-2 primarily infects cells of the respiratory tract via spike glycoprotein binding to angiotensin-converting enzyme (ACE2). Circadian rhythms coordinate an organism's response to its environment and can regulate host susceptibility to virus infection. We demonstrate that silencing the circadian regulator Bmal1 or treating lung epithelial cells with the REV-ERB agonist SR9009 reduces ACE2 expression and inhibits SARS-CoV-2 entry and replication. Importantly, treating infected cells with SR9009 limits SARS-CoV-2 replication and secretion of infectious particles, showing that post-entry steps in the viral life cycle are influenced by the circadian system. Transcriptome analysis revealed that Bmal1 silencing induced interferon-stimulated gene transcripts in Calu-3 lung epithelial cells, providing a mechanism for the circadian pathway to limit SARS-CoV-2 infection. Our study highlights alternative approaches to understand and improve therapeutic targeting of SARS-CoV-2.

Effect of regular and irregular stimulation cycles of dexamethasone on circadian clock in NIH3T3 cells

Animal studies have shown that irregular light-dark cycles cause circadian desynchronization, while few studies have addressed the effect of regular/irregular stimulation cycles of signaling hormones on the cellular clock in vitro. Here, we examined how cellular clocks respond to regular and irregular stimulation cycles of dexamethasone, using NIH3T3 cells transfected with the Bmal1 promoter-driven luciferase (Bmal1-Luc) reporter gene. Cyclic stimulation with dexamethasone at different time intervals (18-28 h, 3 times regularly) revealed that Bmal1-Luc bioluminescence rhythms can be entrained to 22 and 24 h cycles during the stimulation period, but not to other cycles. The rhythm entrained for 24 h cycles persisted for at least one day after the last stimulation. Irregular dexamethasone treatment (16, 24, and 16 h, sequentially; short-term jet lag protocol) resulted in an overall upregulation and phase shifts of the temporal expression of several clock genes and cell cycle genes, including c-Myc and p53. Regular dexamethasone stimulation three times with 24 h cycles also caused upregulation of Per1 and Per2 expression, but not c-Myc and p53 expression. In conclusion, our study identified the entrainable range of the circadian clock in NIH3T3 cells to the dexamethasone stimulation cycle and demonstrated that irregular dexamethasone treatment could disturb the expression of cell cycle genes.