Shift work, occupation and coronary heart disease over 6 years of follow-up in the Helsinki Heart Study

The impact of sleep disturbances on adipocyte function and lipid metabolism

Classically, sleep has been considered to serve an essential restorative function for the brain. However, there are an increasing number of studies linking decreased sleep quantity and/or quality in humans to an increased obesity and diabetes risk. Reductions in sleep quantity or quality lead to an increase in hunger and appetite, which chronically could predispose an individual to obesity. Carefully controlled studies have shown that two nights of insufficient sleep is causally linked to a decrease in disposition index, the most commonly used predictor of an individual's diabetes risk, and impairments in glucose tolerance and insulin sensitivity. Thus, sleep appears to play a critical role in modulating energy metabolism in peripheral tissues. Here we will discuss recent work implicating adipose tissue as a potential direct target of disruption of sleep quality, and explore the potential mechanistic links between sleep, adipose tissue and the global control of energy metabolism in humans.

[Cardiovascular risk factors among shift workers in company of electricity production in the centre of Tunisia]

THE PURPOSE OF THE STUDY

The aim of the present study was to investigate relationship between shift work and the cardiovascular risk factors.

METHODS

A cross-sectional study was included 330 subjects worked in a company of electricity production in the Centre of Tunisia. The collection of data was based on a questionnaire, a clinical exam and biomarkers.

RESULTS

A total of 290 workers was participated in our study (128 shift workers and 162 daytime workers). A raised prevalence but not statistically significant of some factors of cardiovascular risks was found in the shift workers: obesity (25.8 % versus 17.9 %), smoking (44.5 % versus 39.5 %), impaired fasting glucose (11.7 % versus 9.9 %), hypertriglyceridemia (28.1 % versus 25.9 %) and hypercholesterolemia (14.8 % versus 12.4 %). Whereas the prevalence of the alcohol consumption (25.8 % versus 16.0 %) was significantly higher in the shift workers (p=0.04).

CONCLUSION

The high prevalence of the cardiovascular risk factors, observed in our shift workers, justify the adoption of measures to protect this category of workers.

Work and its role in shaping the social gradient in health

Adults with better jobs enjoy better health: job title was, in fact, the social gradient metric first used to study the relationship between social class and chronic disease etiology, a core finding now replicated in most developed countries. What has been less well proved is whether this correlation is causal, and if so, through what mechanisms. During the past decade, much research has been directed at these issues. Best evidence in 2009 suggests that occupation does affect health. Most recent research on the relationship has been directed at disentangling the pathways through which lower-status work leads to adverse health outcomes. This review focuses on six areas of recent progress: (1) the role of status in a hierarchical occupational system; (2) the roles of psychosocial job stressors; (3) effects of workplace physical and chemical hazard exposures; (4) evidence that work organization matters as a contextual factor; (5) implications for the gradient of new forms of nonstandard or "precarious" employment such as contract and shift work; and (6) emerging evidence that women may be impacted differently by adverse working conditions, and possibly more strongly, than men.

Effects of circadian disruption on the cardiometabolic system

The presence of day-night variations in cardiovascular and metabolic functioning is well known. However, only recently it has been shown that cardiovascular and metabolic processes are not only affected by the behavioral sleep/wake cycle but are partly under direct control of the master circadian pacemaker located in the suprachiasmatic nucleus (SCN). Heart rate, cardiac autonomic activity, glucose metabolism and leptin-involved in appetite control-all show circadian variation (i.e., under constant behavioral and environmental conditions). This knowledge of behavioral vs. circadian modulation of cardiometabolic function is of clinical relevance given the morning peak in adverse cardiovascular incidents observed in epidemiological studies and given the increased risk for the development of diabetes, obesity, and cardiovascular disease in shift workers. We will review the evidence for circadian control of cardiometabolic functioning, as well its sensitivity to light and melatonin, and discuss potential implication for therapy.

Postprandial Metabolic Profiles Following Meals and Snacks Eaten during Simulated Night and Day Shift Work

Shift workers are known to have an increased risk of developing cardiovascular disease (CVD) compared with day workers. An important factor contributing to this increased risk could be the increased incidence of postprandial metabolic risk factors for CVD among shift workers, as a consequence of the maladaptation of endogenous circadian rhythms to abrupt changes in shift times. We have previously shown that both simulated and real shift workers showed relatively impaired glucose and lipid tolerance if a single test meal was consumed between 00:00-02:00 h (night shift) compared with 12:00-14:00 h (day shift). The objective of the present study was to extend these observations to compare the cumulative metabolic effect of consecutive snacks/meals, as might normally be consumed throughout a period of night or day shift work. In a randomized crossover study, eight healthy nonobese men (20-33 yrs, BMI 20-25kg/m2) consumed a combination of two meals and a snack on two occasions following a standardized prestudy meal, simulating night and day shift working (total energy 2500 kcal: 40% fat, 50% carbohydrate, 10% protein). Meals were consumed at 01:00/ 13:00 h and 07:00/19:00h, and the snack at 04:00/16:00 h. Blood was taken after an overnight fast, and for 8 h following the first meal on each occasion, for the measurement of glucose, insulin, triacylglycerol (TAG), and nonesterified fatty acids (NEFA). RM-ANOVA (factors time and shift) showed a significant effect of shift for plasma TAG, with higher levels on simulated night compared to day shift (p < 0.05). There was a trend toward an effect of shift for plasma glucose, with higher plasma glucose at night (p = 0.08), and there was a time-shift interaction for plasma insulin levels (p < 0.01). NEFA levels were unaffected by shift. Inspection of the area under the plasma response curve (AUC) following each meal and snack revealed that the differences in lipid tolerance occurred throughout the study, with greatest differences occurring following the mid-shift snack. In contrast, glucose tolerance was relatively impaired following the first night-time meal, with no differences observed following the second meal. Plasma insulin levels were significantly lower following the first meal (p < 0.05), but significantly higher following the second meal (p < 0.01) on the simulated night shift. These findings confirm our previous observations of raised postprandial TAG and glucose at night, and show that sequential meal ingestion has a more pronounced effect on subsequent lipid than carbohydrate tolerance.

We should work less at night

There is growing amount of evidence that doctors' performance is poorer if they work for over-prolonged duties or at night. These working patterns decrease the standard of care and increase the health care expenses. Furthermore, night workers have serious health risks due to their non-physiological work shifts. Effective ways to reduce the overall consequences of fatigue and night work include minimising the amount of work carried out at nighttime and setting up rules for maximal hours for each work shift.

Modafinil in the treatment of excessive sleepiness

The wake-promoting agent modafinil is approved for the treatment of excessive sleepiness associated with obstructive sleep apnea (OSA), shift work disorder (SWD), and narcolepsy. In OSA, modafinil is recommended for use as an adjunct to standard therapies that treat the underlying airway obstruction. This article reviews the literature on modafinil (pharmacology, pharmacokinetics, efficacy, tolerability, and abuse potential), with emphasis on use of modafinil in the treatment of excessive sleepiness in patients with OSA, SWD, and narcolepsy. In large-scale, double-blind, placebo-controlled studies, modafinil improved objectively determined sleep latency, improved overall clinical condition related to severity of sleepiness, and reduced patient-reported sleepiness. Improvements in wakefulness were accompanied by improvements in behavioral alertness, functional status, and health-related quality of life. In patients with SWD, diary data showed modafinil reduced the maximum level of sleepiness during night shift work, level of sleepiness during the commute home, and incidence of accidents or near-accidents during the commute home when compared with placebo. Modafinil was well tolerated, without adversely affecting cardiovascular parameters or scheduled sleep. These findings and those of extension studies which reported improvements were maintained suggest modafinil has a beneficial effect on daily life and well-being in patients with excessive sleepiness associated with OSA, SWD, or narcolepsy.

Dynamic blood pressure changes and recovery under different work shifts in young women

BACKGROUND

Some studies have reported that shift work can affect blood pressure (BP), but few have studied recovery from BP changes occurring during different shifts.

METHODS

We recruited 16 young female nurses working rotating shifts and six working the regular day shift. All received repeated ambulatory BP monitoring (ABPM) during their workdays and following day off.

RESULTS

Our linear mixed-effect model showed that both systolic and diastolic BPs were significantly decreased during sleeping period and significantly increased while on working period, on a work day, but increased during sleeping period after a night shift or evening shift. BP measurements that changed after evening shift usually returned to baseline on consecutive off-duty day after day shift, but they did not completely return to baseline after a night shift (P < 0.05). We also found 69% of those working rotating shifts had at least changed once in dipper/nondipper status. The rates of change in dipper/nondipper status between work day and off-duty day were 33, 44, 50, and 38% for nurses worked in outpatient clinic, night shift, evening shift, and day shift, respectively.

CONCLUSION

Shift work is significantly associated with BP and possibly dipper/nondipper status in young female nurses. Except for those working night shifts, BP levels returned to baseline the off-duty day after day shift. We recommend that potential influence of shift work be considered when evaluating a person's BP.

Estimation of individual reference intervals in small sample sizes

In occupational health studies, the study groups most often comprise healthy subjects performing their work. Sampling is often planned in the most practical way, e.g., sampling of blood in the morning at the work site just after the work starts. Optimal use of reference intervals requires that the population, on which the reference interval is based, is representative for the study group in question. The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) recommends estimating reference interval on at least 120 subjects. It may be costly and difficult to gain group sizes of that order of magnitude for all topics in question. Therefore, new methods to estimate reference intervals for small sample sizes are needed. We present an alternative method based on variance component models. The models are based on data from 37 men and 84 women taking into account biological variation from various variables such as gender, age, BMI, alcohol, smoking, and menopause. The reference intervals were compared to reference intervals calculated using IFCC recommendations. Where comparable, the IFCC calculated reference intervals had a wider range compared to the variance component models presented in this study. The presented method enables occupational health researchers to calculate reference intervals for specific groups, i.e. smokers versus non-smokers, etc. In conclusion, the variance component models provide an appropriate tool to estimate reference intervals based on small sample sizes.

Biological clocks and shift work: circadian dysregulation and potential long-term effects

Long-term epidemiologic studies on large numbers of night and rotating shift workers have suggested an increase in the incidence of breast and colon cancer in these populations. These studies suffer from poor definition and quantification of the work schedules of the exposed subjects. Against this background, the pathophysiology of phase shift and phase adaptation is reviewed. A phase shift as experienced in night and rotating shift work involves desynchronization at the molecular level in the circadian oscillators in the central nervous tissue and in most peripheral tissues of the body. There is a change in the coordination between oscillators with transient loss of control by the master-oscillator (the Suprachiasmatic Nucleus, SCN) in the hypothalamus. The implications of the pathophysiology of phase shift are discussed for long-term health effects and for the design of ergonomic work schedules minimizing the adverse health effects upon the worker.

Situations influencing habits in diet and exercise among nurses working night shift

OBJECTIVES

The aim of the investigation was to describe situations with a significant influence on healthy diet and exercise habits among nurses working night shift.

METHODS

A qualitative descriptive design with a Critical Incident Technique approach was used. Situations were collected by means of interviews with 27 registered/enrolled community nurses.

RESULTS

A total of 143 situations were identified comprising two main areas: coping ability at work and coping ability during leisure hours. Coping ability at work included 81 critical incidents grouped into two categories: the nurses' diet and exercise habits were influenced by social interaction with colleagues at work and by the disruption to their circadian rhythm. Coping ability during leisure hours included 62 critical incidents grouped into two categories: the diet and exercise habits were influenced when the nurses recovered from the disruption to their circadian rhythm and when they took advantage of the freedom of action offered by night work.

CONCLUSIONS

By identifying the factors that influence diet and exercise habits among nurses working night shift, strategies can be developed in order to strengthen the factors with a positive influence.

A prospective cohort study of shift work and risk of ischemic heart disease in Japanese male workers

This study prospectively examined the association between shift work and the risk of ischemic heart disease among Japanese male workers. A baseline survey, which involved 110,792 inhabitants (age range: 40-79 years) from 45 areas throughout Japan, was conducted between 1988 and 1990. The causes of death were identified from death certificates. The analysis was restricted to 17,649 men (age range: 40-59 years) who were employed at the time of the baseline survey. All subjects were asked to indicate the most regular shift work that they had undertaken previously: day work, rotating-shift work, or fixed-night work. The Cox proportional hazards model was used to estimate the risks of shift work for ischemic heart disease. During the 233,869 person-years of follow-up, a total of 1,363 deaths were recorded, 86 of which were due to ischemic heart disease. Compared with the day workers, the rotating-shift workers had a significantly higher risk of death due to ischemic heart disease (relative risk = 2.32, 95% confidence interval: 1.37, 3.95; p = 0.002), whereas fixed-night work was not associated with ischemic heart disease (relative risk = 1.23, 95% confidence interval: 0.49, 3.10; p = 0.658). In addition, subjects with coronary risk factors, such as hypertension, overweight, habitual alcohol consumption, and smoking, were highly susceptible to the effect of rotating-shift work on the risk of death due to ischemic heart disease.

Risk factors for atherosclerosis in healthy employees-a multidisciplinary approach

BACKGROUND

The aim of the study was to investigate the prevalence of early atherosclerosis in healthy workers and the relationship between classical, psychological, and immunological risk factors and atherosclerosis, as well as their predictive value.

METHODS

One hundred healthy managers and 50 office workers aged 35-65 were studied. In all subjects, individual, family, and occupational stress/coping risk factors were evaluated, including plasma levels of biochemical (total cholesterol, LDL, HDL, TG, glucose) and inflammatory-immunological (aCL, anti-beta(2) GPI, oxLDL, HSP, HSCRP) parameters. Carotid artery intima-media thickness (IMT) and atherosclerotic plaques in carotid arteries were assessed with computer analysis of B-mode ultrasound images.

RESULTS

In 107 persons (71%) no changes were found in ultrasound images and in 43 individuals (29%) the presence of plaque was shown. The mean IMT value was 0.0618+/-0.013 mm. Cross-domain analysis showed that core predictors for IMT were age, LDL level, smoking, and occupation (being a manager) (beta=0.33, 0.30, 0.23, and 0.20, respectively); the core predictors for plaque were age, total cholesterol level, and an occupational stressor home-work balance (Wald=7, 6.7, and 5.6, respectively). Immunological factors were not independent predictors.

CONCLUSIONS

In atherosclerosis, not only traditional risk factors (age, lipid disorders, and lifestyle) but also occupational stress factors may play a role. Immunological factors do not seem to play a role in the development of atherosclerosis in a population of healthy workers. The interplay between occupational stress and atherosclerotic changes requires further investigation.

A 12 year prospective study of circulatory disease among Danish shift workers

BACKGROUND

Previous studies of the risk of heart disease after shift work reached different estimates and review authors disagree about the validity of some of the studies. A cross sectional study showed that shift workers had a higher prevalence of nearly every unfavourable work environment factor investigated. Conflicts at work and low decision latitude were more frequent among shift workers, and all-day walking or standing work and part-time jobs were more often found among female shift workers.

OBJECTIVES

To estimate the risk of circulatory disease in a prospective follow up of a representative sample of gainfully employed Danes, considering known or suspected confounding factors.

METHODS

A cohort of 5517 people who were gainfully employed in 1990 were followed up for all hospital treatments due to circulatory diseases (390-458, ICD-8; I00-I99, ICD-10) from 1991 to 2002 inclusive. A log linear Poisson regression model was applied to control confounding factors and calculate the relative risk for 927 men and women working nights, evenings, or other non-day shifts compared to 4579 day workers.

RESULTS

Non-day workers compared to day workers had a relative risk (RR) for all circulatory diseases of 1.31 (95% CI 1.06-1.63). Without control for BMI and smoking, the RR estimate was 1.33 (95% CI 1.07-1.65). For a subgroup of workers with at least three years' seniority, the RR was 1.40 (95% CI 1.09-1.81). The population based aetiological fraction of shift work was estimated to 5%.

CONCLUSION

This study adds to a growing body of evidence suggesting that shift work carries an excess risk of circulatory diseases.

Circadian Disruption, Shift Work and the Risk of Cancer: A Summary of the Evidence and Studies in Seattle

There is increasing interest in the possibility that disruption of normal circadian rhythm may increase the risk of developing cancer. Persons who engage in nightshift work may exhibit altered nighttime melatonin levels and reproductive hormone profiles that could increase the risk of hormone-related diseases, including breast cancer. Epidemiologic studies are now beginning to emerge suggesting that women who work at night, and who experience sleep deprivation, circadian disruption, and exposure to light-at-night are at an increased risk of breast cancer, and possibly colorectal cancer as well. Several studies have been conducted in Seattle recently to investigate the effects of factors that can disrupt circadian rhythm and alter normal nocturnal production of melatonin and reproductive hormones of relevance to breast cancer etiology. Studies completed to date have found: (1) an increased risk of breast cancer associated with indicators of exposure to light-at-night and night shift work; and (2) decreased nocturnal urinary levels of 6-sulphatoxymelatonin associated with exposure to 60-Hz magnetic fields in the bedroom the same night, and a number of other factors including hours of daylight, season, alcohol consumption and body mass index. Recently completed is an experimental crossover study designed to investigate whether exposure to a 60-Hz magnetic field under controlled conditions in the home sleeping environment is associated with a decrease in nocturnal urinary concentration of 6-sulphatoxymelatonin, and an increase in the urinary concentration of luteinizing hormone, follicle stimulating hormone, and estradiol in a sample of healthy women of reproductive age. Presently underway is a study to determine whether working at night is associated with decreased levels of urinary 6-sulphatoxymelatonin, and increased urinary concentrations of the reproductive hormones listed above in a sample of healthy women of reproductive age, and to elucidate characteristics of sleep among night shift workers that are related to the hormone patterns identified. A proposal is under review to extend these studies to a sample of healthy men to investigate whether working at night is associated with decreased levels of urinary 6-sulphatoxymelatonin, and increased concentrations of urinary cortisol and cortisone, urinary levels of a number of androgen metabolites, and serum concentrations of a number of reproductive hormones. Secondarily, the proposed study will elucidate characteristics of sleep among night shift workers that are related to the hormone patterns identified, as well as investigate whether polymorphisms of the genes thought to regulate the human circadian clock are associated with the ability to adapt to night shift work. It is anticipated that collectively these studies will enhance our understanding of the role of circadian disruption in the etiology of cancer.

A Prospective Cohort Study of Employment Status and Mortality from Circulatory Disorders among Japanese Workers

This study prospectively examined the association between employment status (employed or self-employed) and the risk of death from circulatory diseases among Japanese workers. A baseline survey was conducted between 1988 and 1990 among 110,792 inhabitants of 45 areas. Follow-up surveys were conducted annually and causes of death were identified from death certificates. Analysis was restricted to 25,945 individuals (15,434 male and 10,511 female) with ages ranging from 40 to 59 years. These subjects were employed or self-employed at the time of recruitment. The risks of self-employment for death due to circulatory system disease, ischemic heart disease and cerebrovascular disease were estimated using the Cox proportional hazards model. During the 10-year follow-up period (151,817 and 104,870 person-years for males and females, respectively), 720 male and 193 female deaths were recorded. No significant differences were detected between the employed and self-employed workers in the total death risk, or the risk of death from ischemic heart disease. However, self-employed men showed a significantly lower risk of death from cerebrovascular disease compared with employed men (relative risk=0.58; 95% confidence interval=0.35, 0.97). Our findings suggest that employed men are at increased risk of death from cerebrovascular disease compared with self-employed men.

Shift work as an oxidative stressor

Background

Some medical disorders have higher prevalence in shift workers than others. This study was designed to evaluate the effect of night-shift-working on total plasma antioxidant capacity, with respect to the causative role of oxidative stress in induction of some of these disorders.

Methods

Two blood samples were taken from 44 workers with a rotational shift schedule, one after their day shift and one after their night shift. The total plasma antioxidant capacity of each worker was measured through the FRAP method. The impacts of age and weight were also assessed.

Results

The total plasma antioxidant capacity was measured in 44 shift-workers with a mean age of 36.57 years (SD: 10.18) and mean BMI of 26.06 (SD: 4.37) after their day and night shifts. The mean reduction of total plasma antioxidant capacity after the night shift was 105.8 μmol/L (SD: 146.39). Also, a significant correlation was shown between age and weight and total plasma antioxidant capacity. Age and weight were found to be inversely related to total plasma antioxidant capacity; as age and weight increased, the total plasma antioxidant capacity decreased.

Conclusion

Shift work can act as an oxidative stressor and may induce many medical disorders. Aging and obesity in shift workers makes them more sensitive to this hazardous effect.

Cardiac autonomic imbalance in female nurses with shift work

The pathophysiology underlying the shift work-related cardiovascular disease is still poorly understood. The chronic effects of shift work on cardiac autonomic functions were assessed in 47 hospital nurses working under a rotating three-shift system (shift nurses) and 36 public health nurses without shift work (non-shift nurses). The heart rate variability, %LF and %HF (i.e., proportions of sympathetic and vagal activities, respectively), and LF/HF ratio were calculated from the electrocardiographic RR intervals by using autoregressive spectral analysis, and heart rate-corrected QT interval (QTc and QT index) was also measured. The LF/HF ratio, %LF, and QT index were significantly larger in the shift nurses than in the non-shift nurses; also, the power spectral density of HF (PSD(HF)) was significantly decreased in the shift nurses. There was a significant, inverse correlation between the corrected QT interval and PSD(HF) in the non-shift nurses, but not in the shift nurses. It is suggested that shift work in female nurses may cause a sympathodominant state due to depressed vagal tones. Also, a pathophysiology of shift work-related cardiovascular disease, derived from the present and previous findings, may be characterized by the attenuation of the inverse association between the corrected QT interval and vagal activity observed in non-shift workers.

Psychosocial considerations in the European guidelines for prevention of cardiovascular diseases in clinical practice: Third Joint Task Force

The International Society of Behavioral Medicine (ISBM) was one of eight societies that comprised the Third Task Force of European and Other Societies on Prevention of Cardiovascular Disease in Clinical Practice (2003-2004). This task force considered published knowledge from diverse fields related to preventive cardiology including behavioral medicine to improve risk estimation and risk factor management. The scientific evidence supporting the guidelines included findings on low socioeconomic status, social isolation, psychosocial stress, hostility, depression and negative affect, the clustering of psychosocial and lifestyle risk factors, and lifestyle psychosocial interventions. Recommendations for promoting behavior change and management of psychosocial and lifestyle factors in clinical practice include strategies for promoting healthy lifestyle, improving health care provider-patient interactions, implementing multimodal interventions, and managing psychosocial risk factors.

Shiftwork and metabolic risk factors of cardiovascular disease

We conducted this study to examine the relationship between shift work duration and the metabolic risk factors of cardiovascular disease among shift workers. The study population consisted of 226 female hospital nurses and 134 male workers at a firm manufacturing diapers and feminine hygiene materials, whose mean ages were 28.5 yr for the nurses and 29.1 yr for the male workers. The fasting blood sugar level, serum cholesterol, blood pressure, height and weight, waist and hip circumferences (only for the nurses), and numbers of walks during work (as a measure of physical activity) were measured. Using the Karasek's job contents questionnaire, job stress was assessed. Information about the years of work, shift work duration, past medical and behavioral history, including smoking, was obtained by a self-administered questionnaire. With definitions of hypertension as systolic blood pressure (SBP) > or =160 or diastolic blood pressure (DBP) > or =90 mmHg occurring at least once, hypercholesterolemia as serum total cholesterol > or =240 mg/dl, obesity as body mass index (BMI) > or =25 kg/m(2) and as waist to hip ratio (WHR) > or =0.85, we examined the prevalences of metabolic risk factors among subjects. Regression analyses to show the relationships between shift work duration and metabolic risk factors were performed using simple and multivariate models stratified by age, and adjusted for smoking, drinking, job strain and physical activity. Duration of shift work was significantly associated with SBP or cholesterol level among male workers aged 30 or more. Among female nurses, it was inversely associated with DBP (in those who were below 30 yr old) and cholesterol (in those who were aged 30 or more). BMI was non-significantly associated with the duration of shift work in both male workers and female nurses who were 30 yr old or more. WHR in female nurses increased slightly according to increasing duration of shift work. Fasting blood sugar was not significantly associated with the duration of shift work in either sex regardless of age-group. These results suggest an association between shift work duration and the metabolic risk factors of cardiovascular disease.

Effects of shift work on QTc interval and blood pressure in relation to heart rate variability

OBJECTIVES

There is evidence that shift work contributes to excess cardiovascular mortality. The purpose of this study was to determine the effects of shift work on heart rate-corrected QT (QTc) and blood pressure in relation to heart rate variability (CV(RR)).

METHODS

The study population consisted of 153 male shiftworkers and 87 male day workers who were employed at a copper-smelting plant. The QTc interval, total power spectral density (t-PSD) of 100 RR intervals, PSDs with frequencies of 0.01 Hz-0.15 Hz and 0.15 Hz-0.40 Hz (PSD(LF) and PSD(HF)), CV(RR), low frequency (LF) component variability and high frequency (HF) component variability (CCV(LF) and CCV(HF)) and %LF (PSD(LF)/(PSD(LF)+PSD(HF)) .100) were measured (LF and HF components are thought to reflect the sympathetic and parasympathetic activities, respectively).

RESULTS

The QTc interval was significantly longer in the shiftworkers than in the day workers, although there was no significant difference in systolic or diastolic blood pressure between the two groups. Also, the CCV(LF) and log(PSD(LF)) were significantly depressed in the shiftworkers. In the day workers, the QTc interval was significantly related to the CV(RR), log(t-PSD), CCV(HF), log(PSD(HF)),%LF, and log(LF/HF ratio) (partial correlation coefficient r=-0.305, -0.377, -0.312, -0.355, 0.297, and 0.277, respectively). In the shiftworkers only two relations of the QTc interval to non-specific CV(RR) and log(t-PSD) were significant.

CONCLUSION

The clear association between long QTc interval and reduced parasympathetic activity observed in the day workers did not exist in the shiftworkers. Rather, the shiftworkers had a selective reduction in sympathetic drive, which may have compensated for prolonged QTc interval due to shift work. On the other hand, the impact of shift work on hypertension remains unclear, although reduced sympathetic drive in the shiftworkers may explain the absence of differences in blood pressure between shiftworkers and day workers to some extent.

The normal circadian pattern of blood pressure: implications for treatment

Blood pressure fluctuates over 24 h following a circadian rhythm that reaches a peak in the morning shortly after awakening. The onset of many acute cardiovascular and cerebrovascular events shows a synchronous cyclical pattern, with the highest incidence of morbidity and mortality in the early morning hours. Strong, although circumstantial, evidence suggests that the early morning surge in blood pressure may contribute to the onset of acute cardiovascular episodes. Sustained blood pressure control that blunts the early morning blood pressure surge may help to reduce the incidence of these events. Antihypertensive agents are needed that provide smooth and sustained blood pressure control for the full 24 h, including the risky early morning hours. The angiotensin II receptor blocker telmisartan given once daily, because of its long half-life and mechanism of action, is likely to confer benefit in terms of 24-h blood pressure control and may reduce cardiovascular risk at the time of greatest patient vulnerability.

Effects of shift work on autonomic and neuromotor functions in female nurses

Thirty-seven nurses with shift work, working under a rotating three-shift system, and 37 nurses without shift work, having worked during the daytime for one or more years prior to this study, were examined to assess the effects of shift work on cardiac autonomic and neuromotor functions. Their ages ranged from 25 to 58 yr. The electrocardiographic (ECG) R-R interval variability, %LF and %HF (i.e., proportions of sympathetic and parasympathetic activities, respectively), and LF/HF ratio were computed by means of autoregressive spectral and component analyses. The %LF and LF/HF ratio were significantly larger in the nurses with shift work than in those without shift work, although there was no significant difference in the heart rate-corrected QT interval on ECG between them. And, hand-ear coordination differed significantly between the nurses with shift work and those without. Despite the presence of potential selection bias, it is suggested that shift work in nurses may cause not only a long-term sympathodominant state but also some neuromotor impairment.

Occupational exposures and inpatient hospital care for lumbar intervertebral disc disorders among Finns

BACKGROUND

Low back disorders are among the most common health problems in industrialized societies. We examined the relationship between occupational exposures and severe lumbar intervertebral disc disorders (LIDD).

METHODS

Information on inpatient care for LIDD (ICD-10: M51.1-51.9) in Finnish hospitals during 1996 was linked with the 1995 Population Census, and based on occupational title with the Finnish Job Exposure Matrix and the Occupational Lifestyle Matrix. There were 3,863 individuals hospitalized due to LIDD among occupationally active Finns. Poisson regression analyses were made with the total occupationally active population as reference.

RESULTS

In a multivariate analysis in women, accident risk, job control, and three-shift work were associated with hospitalization, together with age, education, personal income, and average body mass index (BMI) by occupation. In men, accident risk and job control were associated with hospital admissions, allowing for age, education, and income.

CONCLUSIONS

Accident risk and job control increased the risk of hospitalization for LIDD in both sexes. Three-shift work and BMI were also predictive of hospital admission among women.

Shiftwork and environment as interactive predictors of work perceptions

Evidence suggests that the work environment may play a role in the elevated risk of adverse health outcomes among shiftworkers compared with dayworkers. Perceived work environment measures (physical stressors, job demand, job control, skill discretion, supervisor support, and safety perceptions) from UK oil industry personnel (N=1,867) were analyzed in relation to shiftwork (day/night rotation vs daywork) and objective work environment (onshore vs offshore). Age, education, job type, and negative affectivity were also included. The Environment * Shiftwork interaction was significant in multivariate tests and in 5 of the 6 univariate analyses. Onshore, shiftworkers perceived their environment significantly less favorably than dayworkers, but differences were less marked offshore. Results are discussed in relation to the demand-control-support model of work stress.

Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry

AIMS

To update the analysis of the cohort mortality and cancer incidence study of employees in the Australian petroleum industry.

METHODS

Employees from 1981 to 1996 were traced through the Australian National Death Index and the National Cancer Statistics Clearing House. Cause specific mortality and cancer incidence were compared with those of the Australian population by means of standardised mortality ratios (SMRs) and standardised incidence ratios (SIRs). Associations between increased incidence of specific cancers and employment in the petroleum industry were tested by trends according to period of first employment, duration of employment, latency, and hydrocarbon exposure, adjusting for personal smoking history where appropriate. Total follow up time was 176 598 person-years for males and 10 253 person-years for females.

RESULTS

A total of 692 of the 15 957 male subjects, and 16 of the 1206 female subjects had died by the cut off date, 31 December 1996. In males, the all-cause SMR and the SMRs for all major disease categories were significantly below unity. There was a non-significant increase of the all-cancer SIR (1.04, 95% CI 0.97 to 1.11). There was a significant increase of the incidence of melanoma (SIR 1.54, 95% CI 1.30 to 1.81), bladder cancer (SIR 1.37, 95% CI 1.00 to 1.83), and prostate cancer (SIR 1.19, 95% CI 1.00 to 1.40), and a marginally significant excess of pleural mesothelioma (SIR 1.80, 95% CI 0.90 to 3.22), leukaemia (SIR 1.39, 95%CI 0.91 to 2.02), and multiple myeloma (SIR 1.72, 95% CI 0.96 to 2.84).

CONCLUSIONS

Most cases of mesothelioma are probably related to past exposure to asbestos in refineries. The melanoma excess may be the result of early diagnosis. The excess bladder cancer has not been observed previously in this industry and is not readily explained. The divergence between cancer incidence and cancer mortality suggests that the "healthy worker effect" may be related to early reporting of curable cancers, leading to increased likelihood of cure and prolonged mean survival time.

Hormonal changes in satisfied and dissatisfied shift workers across a shift cycle

Although the literature claims that shift work is harmful, it overlooks the fact that that many shift workers are satisfied and stay healthy. There is little knowledge of the biological mechanisms mediating the differences in susceptibility. The present study compared satisfied and dissatisfied shift workers with respect to major anabolic and catabolic hormones. Forty-two male shift workers, with an extremely rapidly rotating shift schedule, were divided into two groups according to their ratings of satisfaction with their work hours. Morning blood samples were taken during the first and last morning shift in the shift cycle. Serum was analyzed with respect to testosterone, cortisol, and prolactin. Dissatisfied shift workers had lower morning testosterone than satisfied ones, but they did not significantly differ with respect to cortisol or prolactin. Low testosterone levels were, in addition, associated with a greater sleep need, disturbed sleep/wakefulness, and an increased need for recovery after the work period, the latter being the best predictor of testosterone levels. The only change across the shift cycle concerned a significant decrease of morning cortisol at the end of the shift cycle. High morning cortisol was related to having a morning personality and fewer sleep problems before the morning shift. Dissatisfaction with the shift system seems related to lower testosterone levels, which in turn are related to disturbed sleep/wakefulness and increased need for sleep and recovery. Furthermore, morning cortisol was reduced across a shift cycle. It is suggested that reduced testosterone levels may be part of a mechanism of shift work maladjustment.

Effect of shift work on body mass index: results of a study performed in 319 glucose-tolerant men working in a Southern Italian industry

OBJECTIVE

To examine the influence of shift work on metabolic and cardiovascular risk factors in subjects working in an industry sited in Apulia, Southern Italy.

DESIGN

Cross-sectional study of metabolic effects of shift work in glucose tolerant workers in a chemical industry in southern Italy.

SUBJECTS

The subjects included 319 glucose tolerant male individuals, aged 35-60 y.

MEASUREMENTS

Anthropometric parameters (body mass index (BMI) and waist-to-hip ratio (WHR)), fasting concentrations of glucose, insulin, and lipids (total cholesterol, HDL-cholesterol, triglycerides), the sum of glucose levels during 75 g-oral glucose tolerance test (Sigma-OGTT), and systolic and diastolic blood pressure (SBP and DBP, respectively).

RESULTS

The prevalence of obesity was higher among shift workers compared to day workers, whereas body fat distribution was not different between the two groups. Shift workers had higher BMI than day workers, and shift working was associated with BMI, independently of age and work duration. Shift workers had significantly higher SBP levels, which were independently influenced by BMI, but not by shift work, thus suggesting that the difference in SBP may well be mediated by the increased body fatness.

CONCLUSION

In workers of an industry sited in Southern Italy, shift work may be directly responsible for increased body fatness and is indirectly associated with higher blood pressure levels and some features of metabolic syndrome.

Increased plasma homocysteine levels in shift working bus drivers

BACKGROUND

Previous studies have indicated an association between shift work and cardiovascular disease. There is also considerable epidemiological evidence that hyperhomocysteinemia is an independent risk factor for cardiovascular disorders.

AIMS

To analyse plasma homocysteine levels in shift work bus drivers, and to investigate possible relations with sleep parameters and other biochemical factors.

METHODS

Blood samples were collected from 30 male shift working long-haul bus drivers in a Brazilian sample and analysed for plasma levels of homocysteine, folic acid, vitamin B(12), and serum lipids. A group of 22 daytime workers, matched for age and body mass index served as controls. The incidence of mutations in the gene coding for methylene tetrahydrofolate, an enzyme which is related to hyperhomocysteinemia, was also assessed. Polysomnographic recordings were obtained from the target group.

RESULTS

Bus drivers showed significantly higher levels of plasma homocysteine than the control group (18.57 v 9.43 micro M). Most of the other biochemical, behavioural, and molecular parameters did not differ between groups. Likewise, sleep parameters appeared to be within the normal range.

CONCLUSIONS

The significantly increased plasma homocysteine levels in long-haul bus drivers did not appear to be secondary to other biochemical or behavioural problems in this group. These results suggest that hyperhomocysteinemia may be involved in the increased incidence of cardiovascular diseases observed in shift workers.

Work schedules and fatigue: a prospective cohort study

AIMS

(1) To describe the prevalence of fatigue among employees in different work schedules (day work, three-shift, five-shift, and irregular shift work); (2) to investigate whether different work schedules are related to increasing fatigue over time, while taking into account job title and job characteristics; and (3) to study fatigue among shift workers changing to day work.

METHODS

Data from nine consecutive four-monthly self administered questionnaires from the Maastricht Cohort Study on Fatigue at work (n = 12 095) were used with 32 months of follow up. Day and shift workers were matched on job title.

RESULTS

The prevalence of fatigue was 18.1% in day workers, 28.6% in three-shift, 23.7% in five-shift, and 19.1% in irregular shift workers. For three-shift and five-shift workers substantial higher fatigue levels were observed compared to day workers at baseline measurement. In the course of fatigue over the 32 months of follow up there were only small and insignificant differences between employees in different work schedules. However, among employees fatigued at baseline, fatigue levels decreased faster over time among five-shift workers compared to fatigued day workers. Shift workers changing to day work reported substantially higher fatigue levels prior to change, compared to those remaining in shift work.

CONCLUSIONS

Substantial differences in fatigue existed between day and shift workers. However, as no considerable differences in the course of fatigue were found, these differences have probably developed within a limited time span after starting in a shift work job. Further, evidence was found that fatigue could be an important reason for quitting shift work and moving to day work. Finally, in the relation between work schedules and fatigue, perceived job characteristics might play an important role.

Prevalence of common infections among employees in different work schedules

This study examined the prevalence of common infections among employees in different work schedules. Self-administered questionnaire data from the Maastricht Cohort Study on "Fatigue at Work" (n = 12,140) were used. Job title was used as a matching variable between day and shift workers to control for their different work environment. We used a multilevel analysis of a two-level structure, in which the individual employees (level 1) were nested within job titles (level 2), adjusted for demographics, longstanding disease, health behavior, work-related factors, fatigue and sleep quality. Results from the multilevel analyses showed that, compared to day work, shift work was associated with a higher risk for common infections, with the highest risk in three-shift workers. Compared to day work, shift work was further associated with differences in health, health behavior, sleep, fatigue and perceived job characteristics, factors that may influence the occurrence of infections and should be taken into account in future studies as well.

Is there an association between shift work and having a metabolic syndrome? Results from a population based study of 27,485 people

OBJECTIVES

To explore how metabolic risk factors for cardiovascular disease (CVD) differ between shift workers and day workers in a defined population. Shift work has been associated with an increased risk of CVD. Risk factors and causal pathways for this association are only partly known.

METHODS

A working population of 27,485 people from the Västerbotten intervention program (VIP) has been analysed. Cross sectional data, including blood sampling and questionnaires were collected in a health survey.

RESULTS

Obesity was more prevalent among shift workers in all age strata of women, but only in two out of four age groups in men. Increased triglycerides (>1.7 mmol/l) were more common among two age groups of shift working women but not among men. Low concentrations of high density lipoprotein (HDL) cholesterol (men<0.9 and women<1.0 mmol/l) were present in the youngest age group of shift workers in both men and women. Impaired glucose tolerance was more often found among 60 year old women shift workers. Obesity and high triglycerides persisted as risk factors in shift working men and women after adjusting for age and socioeconomic factors, with an OR of 1.4 for obesity and 1.1 for high triglyceride concentrations. The relative risks for women working shifts versus days with one, two, and three metabolic variables were 1.06, 1.20, and 1.71, respectively. The corresponding relative risks for men were 0.99, 1.30, and 1.63, respectively.

CONCLUSIONS

In this study, obesity, high triglycerides, and low concentrations of HDL cholesterol seem to cluster together more often in shift workers than in day workers, which might indicate an association between shift work and the metabolic syndrome.

Effects of environmental and organizational factors on the health of shiftworkers of a printing company

This study explored the effects of environmental and organizational stressors on the health of shiftworkers in a printing company (n = 124). A questionnaire was used to gather data on work history, organizational factors, psychosocial characteristics, medical history, present health, occupational and non-occupational exposures, and lifestyle factors. The perception of environmental and organizational conditions was associated (P < 0.05) with chronic back pain (odds ratio [OR], 1.29), varicose veins (OR, 1.35), allergic rhinitis (OR, 1.27), depression (OR, 1.45), and gastritis (OR, 1.15). Anxiety scores were associated with allergic rhinitis (OR, 1.14) and skin allergy (OR, 1.09). Shiftwork was a significantly risk factor for conjunctivitis (OR, 3.68), depression (OR, 0.23), cardiac arrhythmia (OR, 7.13), and gastritis (OR, 4.38). Other associations included tenure and chronic back pain (OR, 4.89), toluene exposure and skin allergy (OR, 3.76), worksite and conjunctivitis (OR, 7.0), and worksite and dermatitis (OR, 1.24 to 4.95). The number of hours of exercise per week was associated with varicose veins (OR, 4.33), and alcohol intake was associated with cardiac arrhythmia (OR, 6.74).

Shift work and health

Night work and rotating shift work disrupt the circadian timing system. This disruption may produce significant deleterious symptoms in some workers. Certain medical conditions may be aggravated by shift-work scheduling, and shift workers are at increased risk of experiencing cardiovascular, gastrointestinal, and reproductive dysfunction. Vulnerable individuals may develop clinical depression when working shifts. Primary care practitioners may intervene by providing medical surveillance and educational programs for shift-working patients and their families.

Shiftwork and cardiovascular disease: review of disease mechanisms

This paper reviews the main findings concerning mechanisms explaining the increased risk of coronary heart disease (CHD) in shiftworkers. We discuss a conceptual model, in which three main shiftwork pathways to CHD are postulated--social problems, behavioral change, and disturbed circadian rhythm. Social problems that are associated with shiftwork might lead to stress. Significant shiftwork-related behavioral problems are smoking and unhealthy food habits. Disturbed circadian rhythm might result in sleep deprivation. Unphysiologic timing of physical activity and food intake in relation to circadian rhythms is another possible explanation for the negative impact on the cardiovascular system.

Health effects of work schedules in healthcare professions

Increasing variety in working patterns and the appearance of new forms of shift schedules in the different occupational sectors, including health services, have raised great concern about the quality of working life and job performance. The aim of this paper is to present a systematic review of the literature on the effects on health of irregular schedules in healthcare professionals. Computer and manual searches of databases, and discussion with experts, were used to identify relevant studies. No conclusive evidence was found to favour any particular work system, although there is evidence that extended workdays (9-12 h) should be avoided as much as possible. There is need for carefully designed studies in order to evaluate the long-term consequences of work schedules in healthcare workers.

Shift work, social class, and ischaemic heart disease in middle aged and elderly men; a 22 year follow up in the Copenhagen Male Study

OBJECTIVES

Shift work has been associated with an increased risk of ischaemic heart disease (IHD). Most published studies have had potential problems with confounding by social class. This study explores shift work as a risk factor for IHD after controlling for social class.

METHODS

The Copenhagen male study is a prospective cohort study established in 1970-1 comprising 5249 men aged 40-59. Information obtained included working time, social class, and risk factors for IHD. A second baseline was obtained in 1985-6. The cohort was followed up for 22 years through hospital discharge registers for IHD, and cause of death was recovered from death certificates.

RESULTS

One fifth of the cohort was shift working at entry with a significantly larger proportion of shift workers in lower social classes. Risk of IHD and all cause mortality over 22 years, adjusted for age only, for age and social class, and finally for age, social class, smoking, fitness, height, weight, and sleep disturbances, did not differ between shift and day workers. The relative risk of IHD, adjusted for age and social class was 1.0 (95% confidence interval (95% CI) 0.9-1.2). Men being shift workers in both 1971 and 1985 had the same risk as ex-shift workers in an 8 years follow up from the 1985-6 baseline.

CONCLUSIONS

The present study questions shift work as an independent risk factor for IHD. The results of the study emphasise the importance of controlling adequately for the interplay of shift work and social class.

Circadian Rhythm Sleep Disorders

Delayed sleep phase syndrome (DSPS) is best treated by first using behaviorally scheduled sleeping and arising times to realign the patient's sleep-wake cycle to local time and then by keeping the cycle in synchrony with local time by adherence to a strict daily schedule. Adjunct treatment with morning light exposure or evening melatonin may be useful, and sometimes necessary, to help establish and maintain the new schedule. Coexisting psychiatric or medical illness should be treated before or simultaneously with DSPS. Advanced sleep phase syndrome is rare, and though no treatment has been well studied, evening light exposure and morning melatonin may be helpful. Non-24-hour sleep-wake cycle is common in the blind but occurs rarely in normally sighted persons. Chronic use of evening melatonin may be necessary for these patients to maintain a useful, conventionally timed sleep-wake cycle. Irregular sleep-wake cycles are probably common in persons with multiple handicaps or dementia. Chronic use of melatonin in the evening and exposure to morning light may be useful. Jet lag varies from a minor annoyance to a source of severe impairment of vigilance in the workplace or while driving. Treatment strategies include avoiding naps in the new time zone, staying on the home schedule during short stays, assuming the schedule of the new time zone during longer stays, taking evening melatonin in the new time zone and on return, and using a short-term bedtime sedative in the new time zone and on return. Shift-work sleep disorder affects most night-shift workers, who never fully adjust to trying to sleep in the daytime after their work shifts, often fall asleep while at work, and are at increased risk of development of heart disease and gastrointestinal disorders. Splitting their sleep between after-work morning naps and before-work late-afternoon naps should enable them to get more sleep. Brighter light in the workplace and sleeping in complete darkness may also be of benefit. Long-term use of sedatives is inadvisable for shift workers.

Cardiovascular dysfunction due to shift work

Electrocardiographic, biochemical, and physical data obtained from 237 shift and 115 day workers without any obvious disorders were assessed to clarify the impact of shift work on cardiovascular functions. The heart-rate corrected QT interval (QTc) was significantly longer in the shift workers than in the day workers. However, blood pressure, working duration, and biochemical and other data were comparable between the two work groups. When multiple regression analysis was used, shift/day work was significantly related to the QTc in all of the workers. The adjusted odds ratio of shift work to the prolonged QTc (> or = 440 ms1/2) was 8.15. The prolonged QTc has been thought to contribute to an increased risk of cardiac death. These findings, therefore, suggest that the increased risk for cardiovascular mortality in shift workers may be attributable to prolongation of the QTc.

Shiftwork and myocardial infarction: a case-control study

OBJECTIVES

Previous studies have indicated an association between shiftwork and coronary heart disease. The increased risk could be due to job strain, which could act as a mediator of disease. There is also a possibility that interaction between shiftwork and job strain could occur that may induce or modify the development of disease. We conducted this study to explore the relation between shiftwork, job strain, and myocardial infarction.

METHODS

2006 cases with acute first time myocardial infarction were compared with 2642 controls without symptoms of myocardial infarction, and obtained from the same population that gave rise to the cases (population based case-control study).

RESULTS

Myocardial infarction risk was associated with shiftwork both in men (odds ratio (OR) 1.3, 95% confidence interval (95% CI) 1.1 to 1.6) and women (OR 1.3, 95% CI 0.9 to 1.8). In the age group 45-55, the relative risk was 1.6 in men and 3.0 in women. The results cannot be explained by job strain, age, job education level, or smoking. No interaction was found between shiftwork and job strain.

CONCLUSIONS

The findings indicate that shiftwork is associated with myocardial infarction in both men and women. The mechanism is unclear, but the relation cannot be explained by job strain, smoking, or job education level.