Shift work is a risk factor for increased total cholesterol level: a 14-year prospective cohort study in 6886 male workers

Circadian Clock Disruption and Growth of Kidney Cysts in Autosomal Dominant Polycystic Kidney Disease

Key Points

Lack of Bmal1 , a circadian clock protein in renal collecting ducts disrupted the clock and increased cyst growth and fibrosis in an autosomal dominant polycystic kidney disease mouse model. Bmal1 gene deletion increased cell proliferation by increasing lipogenesis in kidney cells. Thus, circadian clock disruption could be a risk factor for accelerated disease progression in patients with autosomal dominant polycystic kidney disease.

Background

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in the PKD1 and PKD2 genes and often progresses to kidney failure. ADPKD progression is not uniform among patients, suggesting that factors secondary to the PKD1/2 gene mutation could regulate the rate of disease progression. Here, we tested the effect of circadian clock disruption on ADPKD progression. Circadian rhythms are regulated by cell-autonomous circadian clocks composed of clock proteins. BMAL1 is a core constituent of the circadian clock.

Methods

To disrupt the circadian clock, we deleted Bmal1 gene in the renal collecting ducts of the Pkd1 RC/RC (RC/RC) mouse model of ADPKD (RC/RC;Bmal1 f/f;Pkhd1 cre, called double knockout [DKO] mice) and in Pkd1 knockout mouse inner medullary collecting duct cells (Pkd1Bmal1 KO mouse renal inner medullary collecting duct cells). Only male mice were used.

Results

Human nephrectomy ADPKD kidneys showed altered clock gene expression when compared with normal control human kidneys. When compared with RC/RC kidneys, DKO kidneys showed significantly altered clock gene expression, increased cyst growth, cell proliferation, apoptosis, and fibrosis. DKO kidneys also showed increased lipogenesis and cholesterol synthesis–related gene expression and increased tissue triglyceride levels compared with RC/RC kidneys. Similarly, in vitro , Pkd1Bmal1 KO cells showed altered clock genes, increased lipogenesis and cholesterol synthesis–related genes, and reduced fatty acid oxidation–related gene expression compared with Pkd1KO cells. The Pkd1Bmal1 KO cells showed increased cell proliferation compared with Pkd1KO cells, which was rescued by pharmacological inhibition of lipogenesis.

Conclusions

Renal collecting duct–specific Bmal1 gene deletion disrupted the circadian clock and triggered accelerated ADPKD progression by altering lipid metabolism–related gene expression.

Shift work and body composition: a systematic review and meta-analysis

INTRODUCTION

There has been a dramatic increase in the practice of shift work throughout the world. It is known to associate with several adverse health outcomes including increased adiposity. The present study aims to systematically evaluate the literature to find the associations between exposure to shift work and body composition.

EVIDENCE ACQUISITION

Data were obtained using a stepwise search process using keywords in the following online medical databases; PubMed®, Web of Science® and Scopus® for studies published before 31st March 2020. Studies which compared the outcome related to the body composition of shift workers and regular day workers were included. A meta-analysis was performed on body fat percentage (BF%).

EVIDENCE SYNTHESIS

Initial database searching indicated 2311 potentially eligible articles, of which seven studies satisfying the inclusion criteria were selected. The number of participants ranged between 17 to 7318, and the age range of the subjects was between 20-65 years. The studies reported diverse shift schedules including rotating shifts, night, evening shifts, alternate shifts, and regular shifts. Four out of seven studies revealed a higher BF% in shift workers when compared to the non-shift group. The pooled mean difference for BF% between shift workers and regular workers was 1.77% (95% CI: 0.18, 3.35; P=0.03; I2=52%, P>0.12).

CONCLUSIONS

The meta-analysis of the review showed a significant increase in BF% of shift workers when compared to the non-shift group. However, individual studies showed considerable heterogeneity. Therefore in order to further clarify the underlying mechanisms, more and better quality studies on this field are necessary.

Circadian clock disruption and growth of kidney cysts in autosomal dominant polycystic kidney disease

Background

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in the PKD1 and PKD2 genes, and often progresses to kidney failure. ADPKD progression is not uniform among patients, suggesting that factors secondary to the PKD1/2 gene mutation could regulate the rate of disease progression. Here we tested the effect of circadian clock disruption on ADPKD progression. Circadian rhythms are regulated by cell-autonomous circadian clocks composed of clock proteins. BMAL1 is a core constituent of the circadian clock.

Methods

To disrupt the circadian clock, we deleted Bmal1 gene in the renal collecting ducts of the Pkd1 RC/RC (RC/RC) mouse model of ADPKD (RC/RC; Bmal1 f/f ; Pkhd1 cre , called DKO mice), and in Pkd1 knockout mouse inner medullary collecting duct cells ( Pkd1Bmal1 KO mIMCD3 cells). Only male mice were used.

Results

Human nephrectomy ADPKD kidneys and Pkd1 KO mIMCD3 cells showed reduced Bmal1 gene expression compared to normal controls. When compared to RC/RC kidneys, DKO kidneys showed significantly altered clock gene expression, increased cyst growth, cell proliferation, apoptosis and fibrosis. DKO kidneys also showed increased lipogenesis and cholesterol synthesis-related gene expression, and increased tissue triglyceride levels compared to RC/RC kidneys. Similarly, in vitro, Pkd1Bmal1 KO cells showed altered clock genes, increased lipogenesis and cholesterol synthesis-related genes, and reduced fatty-acid oxidation-related gene expression compared to Pkd1KO cells. The Pkd1Bmal1 KO cells showed increased cell proliferation compared to Pkd1KO cells, which was rescued by pharmacological inhibition of lipogenesis.

Conclusion

Renal collecting duct specific Bmal1 gene deletion disrupts the circadian clock and triggers accelerated ADPKD progression by altering lipid metabolism-related gene expression.

Key points

Lack of BMAL1, a circadian clock protein in renal collecting ducts disrupted the clock and increased cyst growth and fibrosis in an ADPKD mouse model.BMAL1 gene deletion increased cell proliferation by increasing lipogenesis in kidney cells.Thus, circadian clock disruption could be a risk factor for accelerated disease progression in patients with ADPKD.

Effect of night shift work on the reduction of glomerular filtration rate using data from Korea Medical Institute (2016-2020)

Background

Shift work increases the risk of chronic diseases, including metabolic diseases. However, studies on the relationship between shift work and renal function are limited. The aim of this study was to investigate the association between shift work and a decreased glomerular filtration rate (GFR).

Methods

Data were evaluated for 1,324,930 workers who visited the Korean Medical Institute from January 1, 2016 to December 31, 2020 and underwent a health checkup. Daytime workers were randomly extracted at a ratio of 1:4 after matching for age and sex. In total, 18,190 workers aged over 40 years were included in the analyses; these included 3,638 shift workers and 14,552 daytime workers. Participants were categorized into the shift work group when they underwent a specific health checkup for night shift work or indicated that they were shift workers in the questionnaire. The odds ratio was calculated using a conditional logistic regression to investigate the relevance of shift work for changes in GFR.

Results

35 workers in the shift group and 54 in the daytime group exhibited an estimated GFR (eGFR) value of < 60 mL/min/1.73m2 (p < 0.01). The difference in eGFR values between two checkups differed significantly depending on the type of work (p < 0.01); the difference in the shift work group (-9.64 mL/min/1.73 m2) was larger than that in the daytime work group (-7.45 mL/min/1.73 m2). The odds ratio for eGFR reduction to < 60 mL/min/1.73 m2 in the shift group versus the daytime group was 4.07 (95% confidence interval: 2.54-6.52), which was statistically significant.

Conclusions

The results of this study suggest that eGFR decreases by a significantly larger value in shift workers than in daytime workers; thus, shift work could be a contributing factor for chronic kidney disease (CKD). Further prospective studies are necessary to validate this finding and identify measures to prevent CKD in shift workers.

Impaired Melatonin Secretion, Oxidative Stress and Metabolic Syndrome in Night Shift Work

Metabolic syndrome has been associated in many studies with working in shifts. Even if the mechanistic details are not fully understood, forced sleep deprivation and exposure to light, as happens during night shifts, or irregular schedules with late or very early onset of the working program, lead to a sleep-wake rhythm misalignment, metabolic dysregulation and oxidative stress. The cyclic melatonin secretion is regulated by the hypothalamic suprachiasmatic nuclei and light exposure. At a central level, melatonin promotes sleep and inhibits wake-signals. Beside this role, melatonin acts as an antioxidant and influences the functionality of the cardiovascular system and of different metabolic processes. This review presents data about the influence of night shifts on melatonin secretion and oxidative stress. Assembling data from epidemiological, experimental and clinical studies contributes to a better understanding of the pathological links between chronodisruption and the metabolic syndrome related to working in shifts.

Associations of recognition at work with subsequent health and quality of life among older working adults

PURPOSE

Recognition for work-an act of conveying non-financial appreciation for an outstanding accomplishment or performance-is the top motivator of employee performance and important contributor to psychologically healthy work. Employee recognition programs are offered by many companies and have been shown to retain top talent, increase job satisfaction, and performance. Yet, evidence on the role of received employee recognition for health and quality of life remains limited. This study examined whether receiving recognition for work was prospectively associated with six indicators of health, quality of life, and loneliness.

METHODS

Data were retrieved from the Survey of Health, Ageing and Retirement in Europe (SHARE), a biennial cross-national panel database of people aged > 50 years. Our sample included 5,048 middle-aged and older working adults.

RESULTS

The results indicated that employees receiving recognition for work reported higher quality of life ([Formula: see text]=0.065, 95% CI = 0.047, 0.082), had lower risks of hypertension (RR = 0.932; 95% CI = 0.899, 0.966) and high blood cholesterol (RR = 0.922; 95% CI = 0.879, 0.967). These associations were independent of demographics, socioeconomic status, personality, prior history of diseases, depression, lifestyle, and work conditions. The set of sensitivity analyses provided substantial evidence for the robustness of the associations between recognition for work and quality of life as well as hypertension but not necessarily with high blood cholesterol.

CONCLUSIONS

Promotion of employee recognition might emerge as a valuable business resource and health policy tool helping middle-aged and older adults maintain health and good quality of life. It may also help willing older adults to remain on the labour market until older age.

Metabolic syndrome and its relationship with shift work in petrochemical workers

BACKGROUND: The metabolic syndrome is a complex of interdependent risk factors for cardiovascular disease and diabetes. Shift work might have an impact on metabolic variables, and be a risk factor for type 2 diabetes. To date, only few studies have been done on the prevalence of MetS in industrial work environments in Iran, and most of them have been conducted on a small sample size. OBJECTIVE: The aim of this study was to evaluate the impact of shift work on prevalence of metabolic syndrome in one of the petrochemical companies in Iran. METHODS: This cross-sectional study was conducted among 692 male workers of a petrochemical company in south-west Iran. Metabolic syndrome was diagnosed according to criteria recommended by Adult Treatment Panel III. In order to determine correlation between MetS and its factors with shift work odds ratio (ORs) for the MetS, 95% confidence level (95% CL), chi-square test and logistic regression analysis were performed. RESULTS: Overall 15.1% of workers were diagnosed with metabolic syndrome and 80% of them were shift workers. A significant difference for prevalence of metabolic syndrome and mean values for body mass index, blood pressure, fast blood sugar, waist circumference among shift workers and non-shift workers were identified (p < 0.001). Compared with the day workers, shift workers had a significantly higher risk of MetS (odds ratio = 4.852; 95% CI 2.34–9.974). CONCLUSIONS: There is an association between metabolic syndrome and shift work in petrochemical workers. Promising intervention strategies are needed for prevention of metabolic disorders for shift workers.

[Examining the association between work-life factors and health disorders/excessive fatigue among Japanese truck drivers]

OBJECTIVES

Karoshi problems (overwork-related deaths and disorders caused by cerebrovascular and cardiovascular diseases) still occur in Japan. Truck drivers, who are in one of the riskiest occupations, are reported to show an increased prevalence of hypertension, obesity, hyperlipidemia, and diabetes, which are characteristic of Karoshi. Their health problems also include excessive fatigue. This cross-sectional study aimed to examine the association between work-life factors and health disorders/excessive fatigue among Japanese truck drivers.

METHODS

We distributed a questionnaire regarding work hours, health status, lifestyle, burden of driving, and excessive fatigue to 5,410 truck drivers and collected a total of 1,947 responses, all from males. The association between work-life factors and health outcomes was evaluated by multivariable logistic regression analysis adjusted for age, drinking, and smoking status.

RESULTS

The prevalence rates of obesity, hypertension, hyperlipidemia, diabetes, cardiovascular disease, cerebrovascular disease, and excessive fatigue were 22.2%, 19.3%, 8.5%, 5.6%, 2.5%, 0.7%, and 6.0%, respectively. Significant associations were observed for long-haul trips (two days or more) with obesity (adjusted odds ratio 1.5 [95% Confidence Interval 1.1-2.1]), local and night trips with hypertension (1.5 [1.0-2.2]), early morning awakening on workdays with obesity (1.5 [1.1-2.1]), being indoor-oriented on weekends with hypertension (1.5 [1.1-2.0]); and heavy burden of driving at night with hyperlipidemia (2.0 [1.3-3.0]). The adjusted odds ratios were significant for waking after sleep onset (2.6 [1.2-5.3]) and lack of sleep satisfaction (2.7 [1.4-5.1]) on workdays, less than six hours of sleep (2.8 [1.0-7.8]) and lack of sleep satisfaction (2.8 [1.5-5.2]) on weekends, 0-3 days off per month (3.6 [1.3-10.2]), and heavy burden of driving at night (2.2 [1.0-4.8]) with excessive fatigue.

CONCLUSIONS

The present findings highlight that night and early morning work, heavy burden of night driving, and the resultant decreases in the quality and quantity of sleep may represent shared risk factors for health disorders and excessive fatigue among truck drivers. Adequate measures should be taken to limit the amount of night and early morning work, reduce the burden of night driving, and ensure days off for sleep opportunities and leisure activities, with the goal of preventing Karoshi.

Melatonin and the circadian system: Keys for health with a focus on sleep

Melatonin (MLT), secreted during the night by the pineal gland, is an efferent hormonal signal of the master circadian clock located in the suprachiasmatic nucleus (SCN). Consequently, it is a reliable phase marker of the SCN clock. If one defines as "chronobiotic," a drug able to influence the phase and/or the period of the circadian clock, MLT is a very potent one. The most convincing data obtained so far come from studies on totally blind individuals. Exogenous MLT administered daily entrains the sleep-wake cycle of these individuals to a 24-h cycle. MLT, however, is not essential to sleep. In nocturnally, active mammals, MLT is released during the night concomitantly with the daily period of wakefulness. Therefore, MLT cannot be simply considered as a sleep hormone, but rather as a signal of darkness. Its role in the circadian system is to reinforce nighttime physiology, including timing of the sleep-wake cycle and other circadian rhythms. MLT exerts its effects on the sleep cycle especially by a direct action on the master circadian clock. The sleep-wake cycle is depending not only on the circadian clock but also on an orchestrated network of different centers in the brain. Thus, the control of sleep-wake rhythm might be explained by a parallel and concomitant action of MLT on the master clock (chronobiotic effect) and on sleep-related structures within the brain. MLT acts through two high-affinity membrane receptors (MT1 and MT2) with striking differences in their distribution pattern. MLT is a powerful synchronizer of human circadian rhythms, thus justifying the use of MLT and MLT agonists in clinical medicine as pharmacological tools to manipulate the sleep-wake cycle, and to treat sleep disorders and other circadian disorders. Available MLT analogs/drugs are all nonspecific MT1/MT2 agonists. The development of new ligands which are highly selectivity for each subtype is clearly a new challenge for the field and will be at the root of new therapeutic agents for curing specific pathologies, including sleep disorders.

Time for Novel Strategies to Mitigate Cardiometabolic Risk in Shift Workers

Circadian disruption induced by shift work is robustly associated with obesity, diabetes, and cardiovascular disease in humans. Less well-known are the mechanisms underlying these associations, and the effectiveness of strategies to reduce cardiometabolic risk in the shift work population. In this review, the different ways in which shift work can deteriorate cardiometabolic health, and how to use this information to reflect on various risk-mitigating strategies, is discussed. While individual strategies appear promising in animal studies, the multifactorial disease risk in shift workers likely requires a multidisciplinary approach. Therefore, the need for individually-tailored combined lifestyle interventions, that could be essential in reducing cardiometabolic disorders in the large population of shift workers in our 24/7 society, is argued.

Shift work, and particularly permanent night shifts, promote dyslipidaemia: A systematic review and meta-analysis

BACKGROUND AND AIMS

Shift work is common worldwide and linked to deleterious cardiovascular effects that might be underlined by dyslipidemia. The aim of this systematic review and meta-analysis is to determine the impact of shiftwork on dyslipidemia.

METHODS

Searching in PubMed, Cochrane Library, Science Direct and Embase databases without language restriction on 15 February 2020, included studies that describe blood lipids levels or a risk measure in shift workers compared with fixed-day workers (controls). Differences by study-level characteristics were estimated using stratified meta-analysis by type of shift work, and meta-regression to examine relations between dyslipidemia and demographic, lifestyle and work characteristics. Estimates were pooled using random-effect meta-analysis.

RESULTS

We included a total of 66 articles, representing 197,063 workers. Shift work globally increased the levels of triglycerides (overall SMD = 0.09; 95CI 0.05 to 0.13; p < 0.001), and globally decreased the levels of c-HDL (-0.08; 95CI -0.12 to -0.03; p = 0.001). Permanent night shift workers were an at-risk type of shift for dyslipidemia with significantly higher blood levels of total cholesterol (0.22; 95CI 0.01 to 0.42; p = 0.043) and triglycerides (0.18; 0.03 to 0.33; p = 0.017), and significantly lower blood levels of c-HDL (-0.16; 95CI -0.32 to 0.00; p = 0.05). Permanent night shift workers were more at-risk for total cholesterol than rotating 3 × 8 shift workers (Coefficient 0.22; 95CI 0.01 to 0.42; p = 0.038) and rotating 2 × 12 shift workers (0.24; 0.02 to 0.46; p = 0.037), and more at-risk for triglycerides than rotating day shift workers (0.21; 95CI 0.03 to 0.38; p = 0.023). Results were non-significant for c-LDL, nor depending on type of shifts.

CONCLUSIONS

Shift work, and particularly permanent night shift, is associated with dyslipidaemia via elevated total cholesterol and triglycerides, and reduced HDL-cholesterol. Our current study provides a practical and valuable strengthening of the evidence-base required for preventive health initiatives and workplace reform.

Dietary and modifiable factors contributing to hyper-LDL-cholesterolemia prevalence in nationwide time series data and the implications for primary prevention strategies

BACKGROUND/OBJECTIVES

A number of studies examined secular trends in blood lipid profiles using time series data of national surveys whereas few studies investigated individual-level factors contributing to such trends. The present study aimed to examine secular trends in dietary and modifiable factors and hyper-LDL-cholesterolemia (HC) prevalence and evaluate their associations using time series data of nationwide surveys.

SUBJECTS/METHODS

The study included 41,073 Korean adults aged ≥ 30 years from the 2005, 2007–2009, 2010–2012, 2013–2015, and 2016 Korea National Health and Nutrition Examination Surveys. Stepwise logistic regression analysis was performed to select significant factors associated with HC, which was defined as serum LDL cholesterol levels ≥130 mg/dL.

RESULTS

The following factors showed a positive association with HC (P < 0.05): for men having higher body mass index (BMI), being married, having an office job, and consuming higher dairy and vegetable oil products; for women having higher age or BMI, having no job or a non-office job, not in a low-income household, and consuming higher dairy products. In the given model, the 2016 survey data showed that a 2 kg/m² reduction in BMI of obese persons resulted in a decreased HC prevalence from 30.8% to 29.3% among men and from 33.6% to 32.5% among women.

CONCLUSIONS

Based on these findings, it is suggested that primary prevention programs should advocate having proper BMI for Korean adults with a high-risk of HC. However, whether discouraging consumption of dairy and vegetable oil products can reduce HC prevalence warrants further studies with a prospective longitudinal design.

MT1 and MT2 melatonin receptors are expressed in nonoverlapping neuronal populations

Melatonin (MLT) exerts its physiological effects principally through two high-affinity membrane receptors MT1 and MT2. Understanding the exact mechanism of MLT action necessitates the use of highly selective agonists/antagonists to stimulate/inhibit a given MLT receptor. The respective distribution of MT1 and MT2 within the CNS and elsewhere is controversial, and here we used a "knock-in" strategy replacing MT1 or MT2 coding sequences with a LacZ reporter. The data show striking differences in the distribution of MT1 and MT2 receptors in the mouse brain: whereas the MT1 subtype was expressed in very few structures (notably including the suprachiasmatic nucleus and pars tuberalis), MT2 subtype receptors were identified within numerous brain regions including the olfactory bulb, forebrain, hippocampus, amygdala and superior colliculus. Co-expression of the two subtypes was observed in very few structures, and even within these areas they were rarely present in the same individual cell. In conclusion, the expression and distribution of MT2 receptors are much more widespread than previously thought, and there is virtually no correspondence between MT1 and MT2 cellular expression. The precise phenotyping of cells/neurons containing MT1 or MT2 receptor subtypes opens new perspectives for the characterization of links between MLT brain targets, MLT actions and specific MLT receptor subtypes.

Effect of circadian rhythm type on serum lipid levels in shift workers: A 5-year cohort study

We investigated how differences in circadian rhythm type affect the health of workers engaged in shift work. Employees, who were newly hired in a steel company between 2007 and 2011, received the Morningness-Eveningness Questionnaire (MEQ) survey. The target participants were 153 male shift workers who were not being treated with any antihyperlipidemic drugs and underwent periodic physical examinations including blood tests at least twice. According to the score of the MEQ at the time of joining the company, we classified the subjects into five types. Longitudinal changes in serum lipid level were estimated among the circadian rhythm types adjusted for age, BMI, and other covariates using a linear mixed model. The regression coefficient of total cholesterol level in the "definitely and moderately morning" group was -17.83 (95% confidence interval (CI): -33.42 to -2.23), and in the "intermediate 'group' was -16.84 [95% CI: -30.40 to -3.28], compared to the moderate evening type." The total cholesterol level was higher in the moderately evening type than in any of the other groups. Between the Morningness-Eveningness (ME) type and Low-density lipoprotein (LDL) cholesterol levels, compared with the "moderately evening type" group, the regression coefficient in the "intermediate type" group was -16.08 (95% CI: -28.79 to -3.37), and in the "definitely and moderately morning type" group was -17.50 [95% CI: -32.11 to -2.88]. The "moderately evening type" group had a higher LDL cholesterol level than any of the other groups. Evening-type circadian rhythm type shift workers are more prone to elevated serum lipid levels.

Night workers have lower levels of antioxidant defenses and higher levels of oxidative stress damage when compared to day workers

The effects of circadian misalignment and work shift on oxidative stress profile of shift workers have not been explored in the literature. The present study aimed to evaluate the role of shift work (day and night) and social jetlag - a measure of circadian misalignment - with oxidative stress markers. A cross-sectional study was performed with 79 men (21–65 years old, 27.56 ± 4.0 kg/m²) who worked the night shift (n = 37) or daytime (n = 42). The analyzed variables included anthropometric measures and determination of systemic levels of markers of oxidative damage and antioxidant defense. Social jetlag was calculated by the absolute difference between the mean sleep point on working and rest days. The night group presented higher systemic values of thiobarbituric acid reactive substances and hydrogen peroxide, and lower levels of nitrite, total antioxidant capacity, and catalase and superoxide dismutase activities in relation to the day group. However, social jetlag was not associated with oxidative stress-related biomarkers analyzed in the night group. These results suggest that the night worker has higher levels of oxidative stress damage and lower levels of antioxidant defenses, while social jetlag was not a possible responsible factor for this condition.

Phase Shifts to a Moderate Intensity Light Exposure in Older Adults: A Preliminary Report

Age-related disrupted sleep has been associated with modifications in the timing of endogenous circadian rhythms. There are studies suggesting a decreased sensitivity of the aging circadian pacemaker to light. In this study, we aimed to test whether a moderate illuminance light stimulus would produce significant phase shifts in older adults, and whether those would fall in a range consistent with the illuminance response curve (IRC) we previously reported in older adults. We conducted an 8-day in-patient study with 12 healthy older participants (mean age [SD], 58.3 [4.2] y, 5 females). A 6.5-h polychromatic white light exposure with a target illuminance of 270 lux was administered beginning in the early biological night. Before and after the light exposure, a circadian phase estimation procedure was carried out, with plasma melatonin data used as a circadian phase marker. The mean phase delay produced by the light stimulus was 1.78 ± 0.77 h. Ten of the 12 phase delay shifts at ~270 lux fell within the 95% predictive interval of the model fit to data from our previous IRC in older adults. This finding demonstrates that the circadian system of healthy older adults is sensitive to the phase-delaying effects of a moderate intensity light stimulus. The magnitude of the observed phase shifts is consistent with the previously described IRC in older adults.

Association between rotating night shift work and metabolic syndrome in Korean workers: differences between 8-hour and 12-hour rotating shift work

This study aimed to analyze the association between the shift work schedule and metabolic syndrome (MetS). This is a retrospective longitudinal study based on the 2015 health checkup data of 2,090 workers evaluated for MetS in 2010 at a general hospital in Korea. The participants were divided according to their shift work schedule into daytime, three-shift (8-h rotation), and two-shift (12-h rotation) workers. The index that indicates the association between the shift work schedule and MetS is the odds ratio (OR) calculated using multivariate logistic regression. The analysis for the entire group of workers indicated that there was positive association between two-shift rotation and MetS (OR=1.58, 95% confidence interval [CI]: 1.09, 2.29). In the analysis of rotating night-shift workers, the years of rotating night shifts, frequency of night-shift work, and sleep disturbance were added to the confounding variables, and two-shift work remained positively associated with MetS (OR=1.72, 95% CI: 1.10, 2.70). The risk of MetS differs based on the shift work schedules they engage in. Hence, structural changes to the shift work schedules are required to prevent MetS in night-shift workers.

What are the effects of psychological stress and physical work on blood lipid profiles?

Blood lipids disorders are prevalent in the world. Some of their risk factors are modifiable such as mental and physical stress which existed in some places such as work environment.Objective of this study was to determine the effects of psychological and physical stress on the lipid profiles. It was a historical cohort study. The people who were employed as general worker were participated. The study was conducted with flexible interview for getting history, lipid profile examination, and a checklist including occupational and nonoccupational risk factors and using the health issues. According to the type of stress exposures, the study population was divided into 5 groups. Groups were followed for lipid profiles. These groups were exposed to psychological stress, physical stress or both of them; mild psychological stress (group 1), mild physical work without psychological stress (group 2), mild psychological stress and mild physical work (group 3), moderate physical work without psychological stress (group 4), and heavy physical work without psychological stress (group 5). Data were analyzed with SPSS 16. ANOVA, χ, and exact test were calculated with considering P < .05 as significant level. Relative risks were calculated with confidence interval 95%. The means of lipid profiles were in normal ranges. The relative risks for triglycerides more than 200 mg/dL was 1.57 (1.02-2.42) and low density lipoprotein (LDL) more than 130 mg/dL was 14.54 (3.54-59.65) in group 1. The relative risks for high density lipoprotein (HDL) less than 45 mg/dL was 14.61 (8.31-25.68) in group 1 and 16.00 (8.30-30.83) in group 3. After multinomial logistic regression they had significant differences. Psychological stress was a risk factor for lipid disorders, and suitable physical activity was protective in this situation.

Dopamine: A Modulator of Circadian Rhythms in the Central Nervous System

Circadian rhythms are daily rhythms that regulate many biological processes – from gene transcription to behavior – and a disruption of these rhythms can lead to a myriad of health risks. Circadian rhythms are entrained by light, and their 24-h oscillation is maintained by a core molecular feedback loop composed of canonical circadian (“clock”) genes and proteins. Different modulators help to maintain the proper rhythmicity of these genes and proteins, and one emerging modulator is dopamine. Dopamine has been shown to have circadian-like activities in the retina, olfactory bulb, striatum, midbrain, and hypothalamus, where it regulates, and is regulated by, clock genes in some of these areas. Thus, it is likely that dopamine is essential to mechanisms that maintain proper rhythmicity of these five brain areas. This review discusses studies that showcase different dopaminergic mechanisms that may be involved with the regulation of these brain areas’ circadian rhythms. Mechanisms include how dopamine and dopamine receptor activity directly and indirectly influence clock genes and proteins, how dopamine’s interactions with gap junctions influence daily neuronal excitability, and how dopamine’s release and effects are gated by low- and high-pass filters. Because the dopamine neurons described in this review also release the inhibitory neurotransmitter GABA which influences clock protein expression in the retina, we discuss articles that explore how GABA may contribute to the actions of dopamine neurons on circadian rhythms. Finally, to understand how the loss of function of dopamine neurons could influence circadian rhythms, we review studies linking the neurodegenerative disease Parkinson’s Disease to disruptions of circadian rhythms in these five brain areas. The purpose of this review is to summarize growing evidence that dopamine is involved in regulating circadian rhythms, either directly or indirectly, in the brain areas discussed here. An appreciation of the growing evidence of dopamine’s influence on circadian rhythms may lead to new treatments including pharmacological agents directed at alleviating the various symptoms of circadian rhythm disruption.

Shiftwork Is Not Associated with Increased Risk of NAFLD: Findings from the National Health and Nutrition Examination Survey

AIMS

There is increased focus on the metabolic impact of shiftwork, especially given the significant number of employees who work nighttime or rotating shifts. Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. We conducted a cross-sectional study to examine the association between shiftwork and the risk of NAFLD.

METHODS

We used aggregated data from the 2005-2006, 2007-2008, and 2009-2010 cycles of the National Health and Nutrition Examination Survey (NHANES). We defined NAFLD by elevated serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels (males: AST > 40 or ALT > 37; females: AST > 31 or ALT > 31) in the absence of excessive alcohol use and viral hepatitis. We defined shiftworkers as participants who self-reported currently working regular night shifts or rotating shifts. We calculated adjusted odds ratios (OR) and 95% confidence intervals (CI) using multivariable logistic regression.

RESULTS

Overall, 8159 participants aged 20-79 years reported working at a job or business using the NHANES Occupation Questionnaire and were included in the analysis. Of these, 11.1% were classified as shiftworkers. Compared to non-shiftworkers, shiftworkers were younger, were less likely to be non-Hispanic White, and have health insurance or health care. The overall prevalence of NAFLD was 15.7%. NAFLD occurred more frequently in shiftworkers (17.0%) than non-shiftworkers (15.5%). However, in the overall multivariable analysis, shiftwork was not associated with the risk of NAFLD (OR 1.11, 95% CI 0.87-1.43).

CONCLUSIONS

The findings from this NHANES-based cross-sectional study do not support an association between shiftwork and increased risk of NAFLD.

The Relationship Between Shift Work and Metabolic Risk Factors: A Systematic Review of Longitudinal Studies

CONTEXT

Although the metabolic health effects of shift work have been extensively studied, a systematic synthesis of the available research is lacking. This review aimed to systematically summarize the available evidence of longitudinal studies linking shift work with metabolic risk factors.

EVIDENCE ACQUISITION

A systematic literature search was performed in 2015. Studies were included if (1) they had a longitudinal design; (2) shift work was studied as the exposure; and (3) the outcome involved a metabolic risk factor, including anthropometric, blood glucose, blood lipid, or blood pressure measures.

EVIDENCE SYNTHESIS

Eligible studies were assessed for their methodologic quality in 2015. A best-evidence synthesis was used to draw conclusions per outcome. Thirty-nine articles describing 22 studies were included. Strong evidence was found for a relation between shift work and increased body weight/BMI, risk for overweight, and impaired glucose tolerance. For the remaining outcomes, there was insufficient evidence.

CONCLUSIONS

Shift work seems to be associated with body weight gain, risk for overweight, and impaired glucose tolerance. Overall, lack of high-methodologic quality studies and inconsistency in findings led to insufficient evidence in assessing the relation between shift work and other metabolic risk factors. To strengthen the evidence, more high-quality longitudinal studies that provide more information on the shift work schedule (e.g., frequency of night shifts, duration in years) are needed. Further, research to the (mediating) role of lifestyle behaviors in the health effects of shift work is recommended, as this may offer potential for preventive strategies.

Bringing obesity to light: Rev-erbα, a central player in light-induced adipogenesis in the zebrafish?

BACKGROUND

Recent studies have led to an expansion of potential factors capable of stimulating obesity. Increasing evidence indicates that environmental factors, including disturbance of circadian rhythms, also contribute to its etiology.

OBJECTIVES

To determine the effects of altered circadian rhythms on adipogenesis and to better understand how circadian and adipogenic regulatory pathways are linked, zebrafish larvae were exposed to various light/dark cycles or hypercaloric feeding (HCF).

METHODS

Clock and adipogenic gene expression was quantitative real time PCR. Adipogenesis was characterized using coherent anti-Stokes Raman scattering microscopy (CARS) and whole-mount lipid composition was analyzed by gas chromatography. The clock protein Rev-erbα and the adipogenesis-regulating protein Pparγ were localized by immunohistochemistry.

RESULTS

Zebrafish larvae exposed to continuous light (LL) had a sevenfold higher prevalence of adipocytes compared with control fish under a 14 h light and 10 h dark cycle. It was also significantly higher compared with that in HCF larvae with control light/dark cycle, which showed a 5.5-fold increase compared with control animals. Although total fatty acid content was unaffected, adipocyte lipid composition was altered in LL zebrafish. In contrast, shifting the onset and duration of the light periods did not affect adipogenesis or total fatty acid content. Gene expression analysis revealed effects of LL and HCF on circadian cyclicity, with increased expression of the clock gene period2 and altered circadian rev-erbα expression in LL larvae. Immunostaining revealed for the first time that Rev-erbα and Pparγ colocalize in adipocytes, which together with the gene expression analysis suggests interplay between Rev-erbα and Ppar isoforms.

CONCLUSIONS

The amount of light, but not shifted light/dark cycles, affected adipogenesis and lipid composition, possibly due to increased period2 expression, which, in turn, enhances Rev-erbα-regulated gene expression. As the pparβδ promoter includes three Rev-erbα binding sites, we hypothesize that pparβδ may be a direct target that ultimately activates Pparγ.

Consequences of Circadian Disruption on Cardiometabolic Health

Cardiovascular disease, diabetes and obesity are highly prevalent diseases associated with reduced quality of life and life expectancy. We discuss a novel risk factor for these cardiometabolic diseases: circadian disruption. Circadian disruption occurs when the internal circadian (∼24-hour) rhythms are not in synchrony with the environment or each other. This paper reviews (1) cardiometabolic health of shift work, which often leads to circadian disruption, (2) effects of experimentally disrupted circadian rhythms on cardiometabolic function, (3) observational studies of sleep timing and behavioral chronotype, and (4) potential mediators linking chronotype and shift work to circadian disruption and cardiometabolic health.

Rodent models to study the metabolic effects of shiftwork in humans

Our current 24-h society requires an increasing number of employees to work nightshifts with millions of people worldwide working during the evening or night. Clear associations have been found between shiftwork and the risk to develop metabolic health problems, such as obesity. An increasing number of studies suggest that the underlying mechanism includes disruption of the rhythmically organized body physiology. Normally, daily 24-h rhythms in physiological processes are controlled by the central clock in the brain in close collaboration with peripheral clocks present throughout the body. Working schedules of shiftworkers greatly interfere with these normal daily rhythms by exposing the individual to contrasting inputs, i.e., at the one hand (dim)light exposure at night, nightly activity and eating and at the other hand daytime sleep and reduced light exposure. Several different animal models are being used to mimic shiftwork and study the mechanism responsible for the observed correlation between shiftwork and metabolic diseases. In this review we aim to provide an overview of the available animal studies with a focus on the four most relevant models that are being used to mimic human shiftwork: altered timing of (1) food intake, (2) activity, (3) sleep, or (4) light exposure. For all studies we scored whether and how relevant metabolic parameters, such as bodyweight, adiposity and plasma glucose were affected by the manipulation. In the discussion, we focus on differences between shiftwork models and animal species (i.e., rat and mouse). In addition, we comment on the complexity of shiftwork as an exposure and the subsequent difficulties when using animal models to investigate this condition. In view of the added value of animal models over human cohorts to study the effects and mechanisms of shiftwork, we conclude with recommendations to improve future research protocols to study the causality between shiftwork and metabolic health problems using animal models.

Evaluation of the effect of shift work on serum cholesterol and triglyceride levels

Background:

Working outside daylight hours (7 am to 7 pm) is called shift work. Shift work is a common practice in many industries and factories such as steel industries, petroleum industries, power plants, and in some services such as medicine and nursing and police forces, in which professionals provide services during day and night.

Objectives:

Considering the contradictory reports of different studies, we decided to evaluate the effect of shift work on cholesterol and triglyceride (TG) levels through a historical cohort on steel industry workers.

Patients and Methods:

This retrospective cohort study was performed on all the staff of Isfahan’s Mobarakeh Steel Company between years 2002 and 2011. There were 5773 participants in this study. Data were collected from the medical records of the staff using the census method. For analysis of data, generalized estimating equation (GEE) regression was used.

Results:

The results showed a significant difference in cholesterol levels between shift workers and day workers on the first observation (P < 0.001), yet no such difference was observed for TG (P = 0.853). Moreover, the results showed that the variables of age, work experience and BMI were not similar between shift workers and day workers. Therefore, to remove the effect of such variables, we used GEE regression. Despite the borderline difference of cholesterol between regular shift workers and day workers, this correlation was not statistically significant (P = 0.051). The results for TG also showed no correlation with shift work.

Conclusions:

According to the findings of this study, there is no relationship between shift work and changes in serum TG and cholesterol. The lack of relationship can be due to shift plans for shift workers, nutrition, or the “Healthy Heart project” at Isfahan Mobarakeh Steel Company.

The effect of shift work on red blood cell distribution width

Limited research demonstrates that shift work (e.g., evening shift, night shift, rotating shift) increases the risk of certain health outcomes, such as hypertriglyceridemia and metabolic syndrome. Red blood cell distribution width (RDW), which is commonly assessed and reported by physicians, is a novel biomarker of cardiovascular disease. However, no study has examined the association of shift work on RDW, which was the purpose of this study. Data from the 2005-2010 NHANES were used. RDW was assessed from a blood sample; shift work was assessed from a questionnaire, and various demographic, behavioral/psychological, occupational, and biological parameters were included as covariates. The fully adjusted model showed that the odds of having an elevated RDW for women on rotating shift vs. day shift increased by 46% (OR=1.46; 95% CI: 1.03-2.08). Women on a rotating shift had increased odds of having an elevated RDW, which is concerning as elevated RDW increases the risk of cardiovascular disease and mortality. Health care professionals are encouraged to include questions about organization of work schedules and their tolerance of such schedules during the patient's consultation.

Shift work and endocrine disorders

The objective of this review was to investigate the impact of shift and night work on metabolic processes and the role of alterations in the sleep-wake cycle and feeding times and environmental changes in the occurrence of metabolic disorders. The literature review was performed by searching three electronic databases for relevant studies published in the last 10 years. The methodological quality of each study was assessed, and best-evidence synthesis was applied to draw conclusions. The literature has shown changes in concentrations of melatonin, cortisol, ghrelin, and leptin among shift workers. Melatonin has been implicated for its role in the synthesis and action of insulin. The action of this hormone also regulates the expression of transporter glucose type 4 or triggers phosphorylation of the insulin receptor. Therefore, a reduction in melatonin can be associated with an increase in insulin resistance and a propensity for the development of diabetes. Moreover, shift work can negatively affect sleep and contribute to sedentarism, unhealthy eating habits, and stress. Recent studies on metabolic processes have increasingly revealed their complexity. Physiological changes induced in workers who invert their activity-rest cycle to fulfill work hours include disruptions in metabolic processes.

Non-alcoholic fatty liver disease: the role of nuclear receptors and circadian rhythmicity

Non-alcoholic fatty liver disease (NAFLD) is the accumulation of triglycerides in the hepatocytes in the absence of excess alcohol intake, and is caused by an imbalance between hepatic synthesis and breakdown of fats, as well as fatty acid storage and disposal. Liver metabolic pathways are driven by circadian biological clocks, and hepatic health is maintained by proper timing of circadian patterns of metabolic gene expression with the alternation of anabolic processes corresponding to feeding/activity during wake times, and catabolic processes characterizing fasting/resting during sleep. A number of nuclear receptors in the liver are expressed rhythmically, bind hormones and metabolites, sense energy flux and expenditure, and connect the metabolic pathways to the molecular clockwork throughout the 24-h day. In this review, we describe the role played by the nuclear receptors in the genesis of NAFLD in relationship with the circadian clock circuitry.

Circadian and behavioural responses to shift work-like schedules of light/dark in the mouse

Background

Disruption of circadian rhythms is associated with several deleterious health consequences and cognitive impairment. It is estimated that as many as one in five workers are exposed to this risk factor due to experiencing some degree of chronodisruption by way of recurring patterns of shift work. It is not presently clear therefore how efficiently the mammalian circadian system entrains to alternative light/dark cycles such as those found in shift work schedules.

Methods

The present study examines male CD-1 mice exposed to three different paradigms of rapidly rotating shift work-like light/dark manipulations compared to control animals maintained on a standard 12:12 h light/dark cycle.

Results

Analysis of circadian patterns of behaviour under such conditions reveals that for fast rotating schedules of light/dark there is minimal circadian entrainment. Further, when placed in constant conditions after a period under the “shift work” lighting conditions there were changes to circadian period associated with the shift work schedules. In contrast to previous studies the shift work-like conditions did not produce changes in animal body-weight. Behavioural testing suggests possible anxiogenic and hyperactive outcomes dependent on rotation speed as animals displayed open field thigmotaxis and hyperlocomotion.

Conclusion

These results indicate that exposure to alternating patterns of light and dark as experienced by millions of shift workers may produce long-lasting changes in both mammalian circadian and neurobehavioural systems.

Anti-clockwise rotating shift work and health: would you prefer 3-shift or 4-shift operation?

BACKGROUND

We explored the association between work schedules involving nightshifts and selected measures of health and whether these associations differed among those working in either 3- or 4-shift cycles.

METHODS

Employees at a German industrial company who worked on a fixed daytime schedule or on one involving nightshifts were invited to participate in this cross-sectional study. Work schedules involving a nightshift were organized into either 3 or 4 shifts rotated anti-clockwise on a weekly basis. Health characteristics included a range of clinical and physiological measures and self-reported data on stress and sleep quality. We assessed the independent association of work schedules involving any nightshift and these health characteristics in separate regression analyses, adjusting for age, gender, smoking, and alcohol consumption.

RESULTS

Nightshift work (N = 133) in general and 3-shift-work (N = 53) in particular was associated with decreased sleep quality (P < 0.001). Compared to those working daytime (N = 632), employees working on a 3-shift cycle had higher adjusted odds of meeting the definition of metabolic syndrome (OR = 2.56 [1.38, 4.75]). Employees working 4-shift cycles were somewhat less likely to have metabolic syndrome (OR = 1.22 [0.73, 2.05]) and had higher parasympathetic activity measured by heart rate variability (OR = 2.20 [1.04, 4.63]).

CONCLUSIONS

Our data suggest important relationships between shift schedule and a selected group of objective and subjective health measures. Additional research that further clarifies potential mechanisms underlying these relationships is needed.

Genomic aspects of NAFLD pathogenesis

Non-alcoholic fatty liver disease (NAFLD) is the most predominant liver disease worldwide and hepatic manifestation of the metabolic syndrome. Its histology spectrum ranges from steatosis, to steatohepatitis (NASH) that can further progress to cirrhosis and hepatocellular carcinoma (HCC). The increasing incidence of NAFLD has contributed to rising numbers of HCC occurrences. NAFLD progression is governed by genetic susceptibility, environmental factors, lifestyle and features of the metabolic syndrome, many of which overlap with HCC. Gene expression profiling and genome wide association studies have identified novel disease pathways and polymorphisms in genes that may be potential biomarkers of NAFLD progression. However, the multifactorial nature of NAFLD and the limited number of sufficiently powered studies are among the current limitations for validated biomarkers of clinical utility. Further studies incorporating the links between circadian regulation and hepatic metabolism might represent an additional direction in the search for predictive biomarkers of liver disease progression and treatment outcomes.

Validation of a questionnaire to screen for shift work disorder

STUDY OBJECTIVE

At least 15% of the full-time work force is shift workers. Working during the overnight hours, early morning start times, and variable or rotating schedules present a challenge to the circadian system, and these shifts are associated with adverse health and safety consequences. Shift work disorder (SWD), a primary (circadian rhythm) sleep disorder indicated by excessive daytime sleepiness and/or insomnia associated with a shiftwork schedule, is under-recognized by primary care physicians. We sought to develop and validate a questionnaire to screen for high risk of SWD in a shift working population.

DESIGN

Shift workers completed a 26-item questionnaire and were evaluated by a sleep specialist (physician) who diagnosed them as either positive or negative for SWD. The physician assessment of SWD was guided by a flow chart that operationalized the ICSD-2 criteria for SWD.

SETTING

18 sleep clinics in the USA.

PATIENTS OR PARTICIPANTS

311 shift workers.

INTERVENTIONS

Not applicable.

MEASUREMENTS AND RESULTS

Responses to the items in the questionnaire were entered into a series of discrimination function analyses to determine the diagnostic value of the items and the fewest number of questions with the best predictive value. The function was then cross-validated. A final 4-item questionnaire has 89% positive predictive value and 62% negative predictive value (sensitivity = 0.74; specificity = 0.82).

CONCLUSIONS

This Shiftwork Disorder Screening Questionnaire may be appropriate for use in primary care settings to aid in the diagnosis of SWD.

Interactions between metabolism and circadian clocks: reciprocal disturbances

Obesity is a medical condition of excess body fat, recognized as a global epidemic. Besides genetic factors, overconsumption of high-energy food and a sedentary lifestyle are major obesogenic causes. A newly identified determinant is altered circadian rhythmicity. To anticipate and adapt to daily changes in the environment, organisms have developed an endogenous circadian timing system, comprising a main circadian clock, located in the suprachiasmatic nucleus (SCN) of the hypothalamus, principally synchronized to the light-dark cycle. Secondary peripheral clocks are found in various tissues, such as the liver, pancreas, and adipose tissue. These clocks control the rhythmic patterns of myriad metabolic processes. We will review the evidence that metabolic dysfunction is associated with circadian disturbances at both central and peripheral levels and, conversely, that disruption of circadian clock functioning can lead to obesity. The roots of these reciprocal interactions will be illustrated by transcriptional crosstalk between metabolic and circadian systems. Chronotherapeutic approaches of dieting to maintain or restore a proper circadian alignment could be useful to limit the magnitude of metabolic risks.

Shift work and cardiovascular risk factors: new knowledge from the past decade

Cardiovascular diseases remain a major public health problem. The involvement of several occupational factors has recently been discussed, notably the organization of work schedules, e.g. shift work. To analyse the progress of knowledge on the relationship between cardiovascular risk factors and shift work. A review of English-language literature dealing with the link between cardiovascular factors and shift workers (published during 2000-2010) was conducted. Studies published in the past 10 years tend to document an impact of shift work on blood pressure, lipid profile (triglyceride levels), metabolic syndrome and, possibly, body mass index. However, the consequences on glucose metabolism are unclear. These results are not yet firmly established, but are supported by strong hypotheses. Some advice could reasonably be proposed to guide the clinical practitioner.

The influence of being overweight on the relationship between shift work and increased total cholesterol level

PURPOSE

The aim of this study was to clarify the influence of shift work on serum total cholesterol (T-Cho) levels according to body mass index (BMI) at entry in Japanese male workers.

METHODS

A 14-year prospective cohort study was conducted in day workers (n = 4079) and alternating shift workers (n = 2807) who received annual health check-ups between 1991 and 2005 in a Japanese steel company. The association between job schedule and increases in T-Cho was investigated using multivariate pooled logistic regression analyses with age, BMI, lifestyle (smoking habit, drinking habit, habitual exercise), and the results of blood chemistries (creatinine, glycosylated hemoglobin A1c, aspartic aminotransferase, γ-glutamyl transpeptidase, uric acid) serving as covariates in those who were not overweight (BMI < 25 kg/m(2), n = 5082) and overweight (BMI ≥ 25 kg/m(2), n = 1804) at entry, respectively. The endpoints in the study were either a 20%, 25%, 30%, 35%, 40%, or 45% increase in T-Cho during the period of observation compared to T-Cho at entry.

RESULTS

In subjects who were not overweight at entry, alternating shift work was associated significantly with five serum T-Cho endpoints (≥20%: odds ratio [OR] = 1.15, 95% confidence interval [CI)] = 1.05, 1.26; ≥25%: OR = 1.17, 95% CI = 1.05, 1.31; ≥35%: OR = 1.24, 95% CI = 1.05, 1.46; ≥40%: OR = 1.30, 95% CI = 1.06, 1.61; ≥45%: OR = 1.31, 95% CI = 1.01, 1.71). However, alternating shift work was not associated with any of the six T-Cho endpoints in subjects who were overweight at entry.

CONCLUSIONS

In the present study, shift work was shown to be a potential risk factor for increased T-Cho in non-overweight Japanese male workers. However, we did not obtain a consistent association between shift work and an increase in T-Cho levels in overweight subjects. The results suggest that the effect of shift work on lipid regulation may be influenced by BMI.

Melatonin: both master clock output and internal time-giver in the circadian clocks network

Daily rhythms in physiological and behavioral processes are controlled by a network of circadian clocks, reset by inputs and delivering circadian signals to the brain and peripheral organs. In mammals, at the top of the network is a master clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus, mainly reset by ambient light. The nocturnal synthesis and release of melatonin by the pineal gland are tightly controlled by the SCN clock and inhibited by light exposure. Several roles of melatonin in the circadian system have been identified. As a major hormonal output, melatonin distributes temporal cues generated by the SCN to the multitude of tissue targets expressing melatonin receptors. In some target structures, like the Pars tuberalis of the adenohypophysis, these melatonin signals can drive daily rhythmicity that would otherwise be lacking. In other target structures, melatonin signals are used for the synchronization (i.e., adjustment of the timing of existing oscillations) of peripheral oscillators, such as the fetal adrenal gland. Due to the expression of melatonin receptors in the SCN, endogenous melatonin is also able to feedback onto the master clock, although its physiological significance needs further characterization. Of note, pharmacological treatment with exogenous melatonin can synchronize the SCN clock. From a clinical point of view, provided that the subject is not exposed to light at night, the daily profile of circulating melatonin provides a reliable estimate of the timing of the human SCN. During the past decade, a number of melatonin agonists have been developed for treating circadian, psychiatric and sleep disorders. These drugs may target the SCN for improving circadian timing or act indirectly at some downstream level of the circadian network to restore proper internal synchronization.

Comparison of peripheral endothelial function in shift versus nonshift workers

Shift working is related to increased cardiovascular morbidity. Peripheral endothelial dysfunction, an inherent feature of early atherosclerosis, has been suggested as a surrogate marker of cardiovascular risk. Whether shift working is associated with peripheral endothelial dysfunction has not been investigated to date. A total of 48 male shift workers (SWs) and 47 male nonshift workers (NSWs) (mean age 43 ± 5 years) were recruited from a glass manufactory. The SWs and NSWs were matched according to age, body mass index, smoking habits, family history of premature coronary artery disease, prevalence of hypercholesterolemia and hypertension, and work place. Their sport habits were also documented. Peripheral endothelial function was assessed using the EndoPAT technique to determine the peripheral arterial tone (PAT) index. According to the study design, no difference was found in the risk factor profiles between the SWs and NSWs. Despite a greater percentage of regular physical activity among the SWs (16.7 vs 4.3%, p = 0.05), shift working was associated with a reduced PAT index compared to working only on the day shift (PAT index 1.73 ± 0.4 vs 1.94 ± 0.5, p = 0.03). In the NSW group, the participants with regular physical training (n = 16) had a greater PAT index than those without regular physical activity (n = 12; PAT index 2.28 ± 0.45 vs 1.86 ± 0.51, p = 0.03). No such difference was found in the SWs. In conclusion, SWs had a reduced PAT index compared with NSWs, suggesting endothelial dysfunction. Therefore, the known increased cardiovascular risk in those shift working might be related to endothelial dysfunction.