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

Pressure Building Against the Clock: The Impact of Circadian Misalignment on Blood Pressure

PURPOSE OF REVIEW

Misalignment between the endogenous biological timing system and behavioral activities (i.e., sleep/wake, eating, activity) contributes to adverse cardiovascular health. In this review, we discuss the effects of recurring circadian misalignment on blood pressure regulation and the implications for hypertension development. Additionally, we highlight emerging therapeutic approaches designed to mitigate the negative cardiovascular consequences elicited by circadian disruption.

RECENT FINDINGS

Circadian misalignment elicited by work schedules that require individuals to be awake during the biological night (i.e., shift work) alters 24-h blood pressure rhythms. Mechanistically, circadian misalignment appears to alter blood pressure via changes in autonomic nervous system balance, variations to sodium retention, dysregulation of endothelial vasodilatory responsiveness, and activation of proinflammatory mechanisms. Recurring circadian misalignment produced by a mismatch in sleep timing on free days vs. work days (i.e., social jetlag) appears to have no direct effects on prevailing blood pressure levels in healthy adults; though, circadian disruptions resulting from social jetlag may increase the risk of hypertension through enhanced sympathetic activation and/or obesity. Furthermore, social jetlag assessment may be a useful metric in shift work populations where the magnitude of circadian misalignment may be greater than in the general population. Circadian misalignment promotes unfavorable changes to 24-h blood pressure rhythms, most notably in shift working populations. While light therapy, melatonin supplementation, and the timing of drug administration may improve cardiovascular outcomes, interventions designed to target the effects of circadian misalignment on blood pressure regulation are warranted.

Shift Work and Metabolic Syndrome Updates: A Systematic Review

Shift work can cause circadian cycles disturbances and misaligns the endogenous rhythms. The physiological variables are driven by the circadian system and, its misalignment, can impair the metabolic functions. Thus, the main objective of this study was to evaluate the metabolic alterations as a result of shift work and night work reported in articles published in the last 5 years, using the eligibility criteria both gender and indexed articles in English language. In order to execute this work, we perform a systematic review according to PRISMA guidelines and searched about Chronobiology Disorders and Night Work, both related to metabolism, in Medline, Lilacs, ScienceDirect and Cochrane. Cross-sectional, cohort and experimental studies with low risk of bias were included. We found a total of 132 articles, and, after the selection process, 16 articles remained to be analyzed. It was observed that shift work can cause circadian misalignment and, consequently, some metabolic parameters alterations such as an impaired glycemic control and insulin functioning, cortisol phase release, cholesterol fractions imbalance, changes in morphological indexes and melatonin secretion. There are some limitations, such as heterogenicity in used databases and the 5 years restriction period, because the effects of sleep disturbance may have been reported earlier. In conclusion, we suggest that shift work interferes with the sleep-wake cycle and eating patterns, which cause crucial physiological alterations that, together, can lead to metabolic syndrome.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shift work. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.

The Effect of Shiftwork on Body Composition: A Comparative Cross-sectional Study Among Health Care Workers

OBJECTIVE

This study compared the body composition parameters between shiftworkers and nonshiftworkers in a hospital setting in Sri Lanka.

METHODS

A comparative cross-sectional study was carried out among a sample of 78 health care workers, recruited by a stratified random sampling technique. Subjects underwent anthropometric and bioimpedentiometric analysis for body composition parameters.

RESULTS

The mean (SD) body fat percentage (BF%) of shiftworking women (40.8 [SD, 6.8%]) was significantly higher than day-working women (36.7% [SD, 5.9%]) ( P < 0.05). Mean BF% between day and shift groups did not significantly differ (33.0% [SD, 6.9%] vs 32.4% [SD, 10.7%]). Body mass index and waist circumference were significantly higher among shiftworking women ( P < 0.05), whereas male workers showed the opposite trend.

CONCLUSION

Prolonged exposure to shiftwork was associated with a higher BF%. Therefore, interventions for shiftworkers must be addressed, focusing on improving body composition.

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.

Night-shift work, breast cancer incidence, and all-cause mortality: an updated meta-analysis of prospective cohort studies

OBJECTIVES

Night-shift work exposure is proposed to link to a wide range of health issues, especially cancer incidence, cancer-specific death, and all-cause death. However, the epidemiological associations among night-shift work exposure, breast cancer, breast cancer-specific death, and all-cause mortality remain inconclusive.

METHODS

We performed an updated systematic review and meta-analysis to confirm potential associations among night-shift work exposure, breast cancer, and all-cause mortality.

RESULTS

A total of 31 prospective cohort studies, involving 9.3 million participants, 31,244 incident breast cancer cases, 12,728 cancer-related deaths, 7882 cardiovascular deaths, and 30,807 all-cause mortalities were included. Overall, the summary RR of incident breast cancer in females for an increase of night-shift work was 1.029 (95% CI 1.003-1.055). Compared with standard day workers, night-shift workers had a statistically significantly increased RR (1.086, 95% CI 1.032-1.142) for breast cancer incidence in the subgroup of > 10 years exposure. Furthermore, a positive association was revealed in subgroup studies of rotating night-shift work (RR = 1.053, 95% CI 1.018-1.090). A significant increased risk of cardiovascular mortality was demonstrated in the night-shift work group (RR = 1.031; 95% CI 1.006-1.057).

CONCLUSION

Our systematic review and meta-analysis provided convincing evidence supporting positive associations among night-shift work exposure, breast cancer incidence, and cardiovascular mortality. Taken together, night-shift work exposure significantly increased the risk of breast cancer morbidity by 2.9% for total, 8.6% for the subgroup of more than 10 years night-shift work, and 5.3% for rotating night-shift work. In addition, night-shift work increased the risk of cardiovascular mortality by 3.1%.

Associations of shift work and night work with risk of all-cause, cardiovascular and cancer mortality: a meta-analysis of cohort studies

BACKGROUND

Epidemiological studies on the relationship of shift work or night work with risk of total and cause-specific mortality have given conflicting results. We aimed at conducting a meta-analysis to summarize the evidence from cohort studies.

METHODS

Embase, PubMed, Web of Science and Scopus databases were searched for eligible studies up to Mar 2021. Cohort studies evaluating the associations of shift work or night work with risk of all-cause, cardiovascular or cancer mortality were reviewed. Study-specific risk estimates were pooled by fixed-effect models when the heterogeneity was not detected; otherwise, random-effect models were employed.

RESULTS

We identified seventeen eligible articles (sixteen cohorts). A total of 958,674 cohort participants were included, with 38,413 total deaths, 24,713 cardiovascular deaths and 10,219 cancer deaths during follow-up. According to the Newcastle-Ottawa Scale, fifteen studies were considered as relatively high quality with low risk of bias. Compared with regular daytime workers, the pooled relative risks for all-cause, cardiovascular and cancer mortality were 1.02 (95% CI: 0.99, 1.06), 1.18 (95% CI: 0.94, 1.47) and 1.05 (95% CI: 0.83, 1.34) for those ever exposing to shift work, respectively. Compared with daytime workers or those never exposing to night work, the pooled relative risks for all-cause, cardiovascular and cancer mortality were 1.06 (95% CI: 1.03, 1.08), 1.15 (95% CI: 1.03, 1.29) and 1.04 (95% CI: 1.00, 1.08) for those ever exposing to night work, respectively. Moderate to high level of heterogeneity across the studies was detected. Publication bias was not detected.

CONCLUSION

Night work may be associated with higher risk of all-cause, cardiovascular and cancer mortality, suggesting that night workers compared with daytime workers may be at higher risk of death, especially due to cardiovascular disease.

Night work, mortality, and the link to occupational group and sex

Objective:

Night shifts are associated with several major diseases. Mortality has been studied only to a limited extent, and the association with night shifts remains unclear. The purpose of the present study was to investigate the association between duration of night shift exposure and mortality in a large sample from the Swedish Twin Registry (the SALT cohort).

Methods:

Cox proportional hazards regression models were used to analyze the data (N=42 731) over a follow-up period of 18 years, with years of night shift work as the exposure variable and adjustment for lifestyle factors and age, and stratification on gender and occupational group.

Results:

The hazard ratio (HR) for “ever” night shifts for total mortality was 1.07 [95% confidence interval (CI) 1.01–1.15] but 1.15 (95% CI 1.07–1.25) for longer exposure (>5 years). Also, HR for cause-specific mortality due to cardiovascular disease was significant, with higher HR for longer night shift exposure. Mortality due to cancer was significant for longer exposure only. White-collar workers showed significant HR for longer exposure. In particular, male white-collar workers showed a significant HR, with a highest value for longer exposure [HR 1.28 (95% CI 1.09–1.49)]. Heredity did not influence the results significantly.

Conclusions:

Long duration of exposure to night shift work is associated with increased mortality, particularly in male white-collar workers. The lack of effects of accumulated exposure suggests that the results should be interpreted with caution.

Working Time Society consensus statements: Evidence-based effects of shift work on physical and mental health

Potential effects of shift work on health are probably related to the misalignment between the light-dark cycle and the human activity-rest cycle. Light exposure at night mediates these effects, including social misalignment and leads to an inversion of activity and rest, which, in turn, is linked to changes in behaviours. This article reviews the epidemiological evidence on the association between shift work and health, and possible mechanisms underlying this association. First, evidence from findings of the meta-analyses and systematic reviews published in the last 10 yr is presented. In addition, it reports the larger single-occupation studies and recent large population-based studies of the general workforce. Koch's postulates were used to evaluate the evidence related to the development of disease as a result of exposure to shift work. Finally, we discussed limitations of the multiple pathways that link shift work with specific disorders and the methodological challenges facing shift work research. We concluded that the clearest indications of shift work being the cause of a disease are given when there is a substantial body of evidence from high quality field studies showing an association and there is good evidence from laboratory studies supporting a causal explanation of the link.

Night-time work and all-cause mortality in the general working population of Denmark

PURPOSE

A recent study among female nurses in Denmark found an increased mortality among night-time workers, which has raised concerns about the sufficiency of the EU Working Time Directive. The aim of the present study was to examine the relationship between night-time work and all-cause mortality among full-time employees in the general workforce of Denmark.

METHODS

Interview data from the Danish Labour Force Surveys, 1999-2013, were linked to national registers with individual-level data on occupation, industry, socioeconomic status (SES), emigrations and deaths. The participants (N = 159,933) were followed from the end of the calendar year of the interview until the end of 2014. Poisson regression was used to estimate rate ratios for all-cause mortality, with and without stratification by sex and socioeconomic status. A likelihood ratio test was used to test the overall null-hypothesis, which stated that the mortality rates were independent of night-time work, SES × night-time work and sex × night-time work.

RESULTS

The likelihood ratio test did not reject the null hypothesis (p = 0.14). The rate ratio for all-cause mortality among employees with vs. without night-time work was estimated at 1.07 (95% CI 0.97-1.19) after adjustment for age, sex, SES, calendar time, weekly working hours and time passed since the start of follow-up.

CONCLUSIONS

The present study did not find any statistically significant associations between night-time work and all-cause mortality among employees in the general workforce of Denmark.

Cardiovascular Risk Factors in White Collar Workers Under Shift Work

Shift work is associated with circadian disruption, disturbs sleep and social life, and modifies disease risk factors, and thus can potentially contribute to various chronic diseases including cardiovascular diseases. The aim of the study was to follow cardiovascular risk in white collar workers under shift work. Cardiovascular risk was studied in sound-engineering staff in sound-recording production. The study encompassed 168 employees (46% males and 54% females) working under shift work of age 48.04 ± 8.8 years and length of service 21.6 ± 4.6 years. Our data show that 31.1% of the investigated employees were hypertensive, of which 22.6% had preliminary physician’s diagnosis of arterial hypertension, showing comparatively high rates of undiagnosed hypertension, higher in males in comparison to females. The TC and HDL-C were slightly higher with the females, while the triglycerides and TC/HDL-C ratio with the males. High rates of smoking, physical inactivity, overweight and obesity were found with both genders, slightly higher with the females. The preventive approach incorporating regular medical surveillance of shift workers and health promotion covering both life style factors and shift work organization is needed for tackling CVD in shift workers for better cardiovascular health.

Study of shift work and risk of coronary events

Background: The effects of shift work on coronary heart diseases (CHD) are well described. Most of the studies on coronary events in shift workers are supportive of the hypothesis that they are at increased risk.

Objective: The objective of this study was to investigate the relation shift work has to risk of CHD in a cohort of men from different Asian races working in a fertilizer plant in the Middle East. Design: This is a case series of cohort study.

Subjects: The medical records for 2562 staff employed at the plant, from the start of the company in 1972 till 2003, were surveyed. Of these, 648 were shift workers and 1914 were daytime workers. A total of 223 employees had cardiovascular event.

Methods: For each case we recorded the date and age at start of employment, and the age at the time of diagnosis. Data from their last medical examination in the company were used to calculate their BMI, and to register whether they were smokers, had diabetes, or were senior or intermediate staff. Univariate and multivariate statistical analyses were performed.

Results: The incidence of CHD is significantly higher in shift workers (13.5%) compared with the daytime workers (7.1%). Also, there was a statistically significant difference between shift workers and daytime workers concerning hypertension and cerebrovascular incidents.

Conclusion: Our results suggest the possibility of an overall relationship between shift work and cardiovascular diseases.

Associations of Short Sleep and Shift Work Status with Hypertension among Black and White Americans

Objective. The purpose of this study was to investigate whether short sleepers (<6 hrs) who worked the non-day-shift were at greater likelihood of reporting hypertension and if these associations varied by individuals' ethnicity. Methods. Analysis was based on the 2010 National Health Interview Survey (NHIS). A total of 59,199 American adults provided valid data for the present analyses (mean age = 46.2 ± 17.7 years; 51.5% were female). Respondents provided work schedule and estimated habitual sleep durations as well as self-report of chronic conditions. Results. Of the sample, 30.8% reported a diagnosis of hypertension, 79.1% reported daytime shift work, 11.0% reported rotating shift work, and 4.0% reported night shift work. Logistic regression analysis showed that shift work was significantly associated with hypertension among Blacks [OR = 1.35, CI: 1.06–1.72. P < 0.05], but not among Whites [OR = 1.01, CI: 0.85–1.20, NS]. Black shift workers sleeping less than 6 hours had significantly increased odds of reporting hypertension [OR = 1.81, CI: 1.29–2.54, P < 0.01], while their White counterparts did not [OR = 1.17, CI: 0.90–1.52, NS]. Conclusions. Findings suggest that Black Americans working the non-day-shift especially with short sleep duration have increased odds of reporting hypertension.

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.

Night-shift work increases morbidity of breast cancer and all-cause mortality: a meta-analysis of 16 prospective cohort studies

Night-shift work (NSW) has previously been related to incidents of breast cancer and all-cause mortality, but many published studies have reported inconclusive results. The aim of the present study was to quantify a potential dose-effect relationship between NSW and morbidity of breast cancer, and to evaluate the association between NSW and risk of all-cause mortality. The outcomes included NSW, morbidity of breast cancer, cardiovascular mortality, cancer-related mortality, and all-cause mortality. Sixteen investigations were included, involving 2,020,641 participants, 10,004 incident breast cancer cases, 7185 cancer-related deaths, 4820 cardiovascular end points, and 2480 all-cause mortalities. The summary risk ratio (RR) of incident breast cancer for an increase of NSW was 1.057 [95% confidence interval (CI) 1.014-1.102; test for heterogeneity p = 0.358, I(2) = 9.2%]. The combined RR (95% CI) of breast cancer risk for NSW vs daytime work was: 1.029 (0.969-1.093) in the <5-year subgroup, 1.019 (1.001-1.038) for 5-year incremental risk, 1.025 (1.006-1.044) for 5- to 10-year exposure times, 1.074 (1.010-1.142) in the 10- to 20-year subgroup, and 1.088 (1.012-1.169) for >20-year exposure lengths. The overall RR was 1.089 (95% CI 1.016-1.166) in a fixed-effects model (test for heterogeneity p = 0.838, I(2) = 0%) comparing rotating NSW and day work. Night-shift work was associated with an increased risk of cardiovascular death (RR 1.027, 95% CI 1.001-1.053), and all-cause death 1.253 (95% CI 0.786-1.997). In summary, NSW increased the risk of breast cancer morbidity by: 1.9% for 5 years, 2.5% for 5-10 years, 7.4% for 10-20 years, and 8.8% for >20-years of NSW. Additionally, rotating NSW enhanced the morbidity of breast cancer by 8.9%. Moreover, NSW was associated with a 2.7% increase in cardiovascular death.

Total and cause-specific mortality of U.S. nurses working rotating night shifts

BACKGROUND

Rotating night shift work imposes circadian strain and is linked to the risk of several chronic diseases.

PURPOSE

To examine associations between rotating night shift work and all-cause; cardiovascular disease (CVD); and cancer mortality in a prospective cohort study of 74,862 registered U.S. nurses from the Nurses' Health Study.

METHODS

Lifetime rotating night shift work (defined as ≥3 nights/month) information was collected in 1988. During 22 years (1988-2010) of follow-up, 14,181 deaths were documented, including 3,062 CVD and 5,413 cancer deaths. Cox proportional hazards models estimated multivariable-adjusted hazard ratios (HRs) and 95% CIs.

RESULTS

All-cause and CVD mortality were significantly increased among women with ≥5 years of rotating night shift work, compared to women who never worked night shifts. Specifically, for women with 6-14 and ≥15 years of rotating night shift work, the HRs were 1.11 (95% CI=1.06, 1.17) and 1.11 (95% CI=1.05, 1.18) for all-cause mortality and 1.19 (95% CI=1.07, 1.33) and 1.23 (95% CI=1.09, 1.38) for CVD mortality. There was no significant association between rotating night shift work and all-cancer mortality (HR≥15years=1.08, 95% CI=0.98, 1.19) or mortality of any individual cancer, with the exception of lung cancer (HR≥15years=1.25, 95% CI=1.04, 1.51).

CONCLUSIONS

Women working rotating night shifts for ≥5 years have a modest increase in all-cause and CVD mortality; those working ≥15 years of rotating night shift work have a modest increase in lung cancer mortality. These results add to prior evidence of a potentially detrimental effect of rotating night shift work on health and longevity.

Work schedules and 11-year progression of carotid atherosclerosis in middle-aged Finnish men

OBJECTIVES

This study investigated the relationship between different work schedules and progression of carotid atherosclerosis, an early indicator of cardiovascular disease (CVD).

METHODS

We studied 621 men, aged 42-60 years, in the prospective Kuopio Ischemic Heart Disease Risk Factor Study cohort. Using multivariable regressions adjusting for 22 covariates including total time worked during follow-up, we evaluated the associations of baseline work schedules with 11-year progression of ultrasonographically assessed carotid intima-media thickness (IMT), and their variation by preexisting CVD.

RESULTS

Standard daytime work, weekend shifts, and evening/night/rotating shifts were associated with 31%, 37%, and 33% increases in IMT, respectively. Compared to daytime workers, weekend workers experienced a faster progression of carotid atherosclerosis [relative change ratio (RCR) = 1.05, 95% CI: 1.00-1.09)]. This ratio was higher among men who had preexisting CVD.

CONCLUSIONS

Weekend shifts, more than standard daytime work, appear to accelerate carotid atherosclerosis progression among middle-aged Finnish men, especially those with pre-existing CVD.

Twenty-four hour pattern of intraocular pressure and ocular perfusion pressure in night shift workers

PURPOSE

To investigate the intraocular pressure (IOP) and ocular perfusion pressure (OPP) in night shift workers.

METHODS

Seventy-one healthy individuals who work the night shift were evaluated. IOP and OPP were measured in the sitting position in each participant. Measurements were obtained at rest time (09:00, 12:00, 16:00) and night-shift time (20:00, 24:00, 04:00, 08:00).

RESULTS

The mean age of the 33 females and 38 males was 35.6 ± 7.5 years (range 20-53 years). Mean IOP values were different between the measurements at 9:00 and 12:00 (p = 0.00), at 9:00 and 16:00 (p = 0.00), at 12:00 and 16:00 (p = 0.00), at 16:00 and 24:00 (p = 0.02), at 24:00 and 04:00 (p = 0.02), and at 24:00 and 08:00 (p = 0.00). Mean OPP values were significantly different only between the measurements at 9:00 and 20:00 (p = 0.01).

CONCLUSION

This study revealed that IOP and OPP in night shift workers show 24-hour variations.

Influence of Differences in Their Jobs on Cardiovascular Risk Factors in Male Blue-collar Shift Workers in Their Fifties

This study examined relationships between different job types of shift work and hypertension, obesity, and dyslipidemia. Male blue-collar workers 50-59 years of age (n = 210) on the same three-shift schedule in a pulp and paper mill were divided into two groups; 118 in paper manufacturing (group 1) and 92 in the chemical products section (group 2). Only the frequency of hypertension differed significantly (p = 0.012) between the groups, 52.2% (n = 48) in group 2 vs 33.9% (n = 40) in group 1. The odds ratio for group 2 in relation to hypertension was 2.3 (95% CI 1.2-4.2). These results indicate a positive association between job type of shift work and hypertension and suggest that different job types of shift workers should not be combined when the effects of shift work on blood pressure are being examined.

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.

A retrospective cohort study of shift work and risk of cancer-specific mortality in German male chemical workers

OBJECTIVES

Human evidence of carcinogenicity concerning shift work is inconsistent. In a previous study, we observed no elevated risk of total mortality in shift workers followed up until the end of 2006. The present study aimed to investigate cancer-specific mortality, relative to shift work.

METHODS

The cohort consisted of male production workers (14,038 shift work and 17,105 day work), employed at BASF Ludwigshafen for at least 1 year between 1995 and 2005. Vital status was followed from 2000 to 2009. Cause-specific mortality was obtained from death certificates. Exposure to shift work was measured both as a dichotomous and continuous variable. While lifetime job history was not available, job duration in the company was derived from personal data, which was then categorized at the quartiles. Cox proportional hazard model was used to adjust for potential confounders, in which job duration was treated as a time-dependent covariate.

RESULTS

Between 2000 and 2009, there were 513 and 549 deaths among rotating shift and day work employees, respectively. Risks of total and cancer-specific mortalities were marginally lower among shift workers when taking age at entry and job level into consideration and were statistically significantly lower when cigarette smoking, alcohol intake, job duration, and chronic disease prevalence at entry to follow-up were included as explanatory factors. With respect to mortality risks in relation to exposure duration, no increased risks were found in any of the exposure groups after full adjustment and there was no apparent trend suggesting an exposure-response relation with duration of shift work.

CONCLUSIONS

The present analysis extends and confirms our previous finding of no excess risk of mortality associated with work in the shift system employed at BASF Ludwigshafen. More specifically, there is also no indication of an increased risk of mortality due to cancer.

Shift work and vascular events: systematic review and meta-analysis

OBJECTIVE

To synthesise the association of shift work with major vascular events as reported in the literature.

DATA SOURCES

Systematic searches of major bibliographic databases, contact with experts in the field, and review of reference lists of primary articles, review papers, and guidelines.

STUDY SELECTION

Observational studies that reported risk ratios for vascular morbidity, vascular mortality, or all cause mortality in relation to shift work were included; control groups could be non-shift ("day") workers or the general population.

DATA EXTRACTION

Study quality was assessed with the Downs and Black scale for observational studies. The three primary outcomes were myocardial infarction, ischaemic stroke, and any coronary event. Heterogeneity was measured with the I(2) statistic and computed random effects models.

RESULTS

34 studies in 2,011,935 people were identified. Shift work was associated with myocardial infarction (risk ratio 1.23, 95% confidence interval 1.15 to 1.31; I(2)=0) and ischaemic stroke (1.05, 1.01 to 1.09; I(2)=0). Coronary events were also increased (risk ratio 1.24, 1.10 to 1.39), albeit with significant heterogeneity across studies (I(2)=85%). Pooled risk ratios were significant for both unadjusted analyses and analyses adjusted for risk factors. All shift work schedules with the exception of evening shifts were associated with a statistically higher risk of coronary events. Shift work was not associated with increased rates of mortality (whether vascular cause specific or overall). Presence or absence of adjustment for smoking and socioeconomic status was not a source of heterogeneity in the primary studies. 6598 myocardial infarctions, 17,359 coronary events, and 1854 ischaemic strokes occurred. On the basis of the Canadian prevalence of shift work of 32.8%, the population attributable risks related to shift work were 7.0% for myocardial infarction, 7.3% for all coronary events, and 1.6% for ischaemic stroke.

CONCLUSIONS

Shift work is associated with vascular events, which may have implications for public policy and occupational medicine.

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.

Circadian Aspects of Postprandial Metabolism

Time-dependent variations in the hormonal and metabolic responses to food are of importance to human health, as postprandial metabolic responses have been implicated as risk factors in a number of major diseases, including cardiovascular disease. Early work reported decreasing glucose tolerance in the evening and at night with evidence for insulin resistance at night. Subsequently an endogenous circadian component, assessed in constant routine (CR), as well as an influence of sleep time, was described for glucose and insulin. Plasma triacylglycerol (TAG), the major lipid component of dietary fat circulating after a meal, also appears to be influenced by both the circadian clock and sleep time with higher levels during biological night (defined as the time between the onset and offset of melatonin secretion) despite identical hourly nutrient intake. These time-dependent differences in postprandial responses have implications for shiftworkers. In the case of an unadapted night shift worker, meals during work time will be taken during biological night. In simulated night shift conditions the TAG response to a standard meal, preceded by either a low-fat or a high-fat premeal, was higher after a nighttime meal than during a daytime meal, and the day/night difference was larger in men than in women. In real night shift workers in Antarctica, insulin, glucose, and TAG all showed an increased response after a nighttime meal (second day of night shift) compared to a daytime meal. Night shift workers are reported to have an approximately 1.5 times higher incidence of heart disease risk and also demonstrate higher TAG levels compared with matched dayworkers. As both insulin resistance and elevated circulating TAG are independent risk factors for heart disease, it is possible that meals at night may contribute to this risk.

Influence of the Circadian System on Disease Severity

The severity of many diseases varies across the day and night. For example, adverse cardiovascular incidents peak in the morning, asthma is often worse at night and temporal lobe epileptic seizures are most prevalent in the afternoon. These patterns may be due to the day/night rhythm in environment and behavior, and/or endogenous circadian rhythms in physiology. Furthermore, chronic misalignment between the endogenous circadian timing system and the behavioral cycles could be a cause of increased risk of diabetes, obesity, cardiovascular disease and certain cancers in shift workers. Here we describe the magnitude, relevance and potential biological basis of such daily changes in disease severity and of circadian/behavioral misalignment, and present how these insights may help in the development of appropriate chronotherapy.

A longitudinal study on the effect of shift work on weight gain in male Japanese workers

OBJECTIVE

This study compared the effect of alternating shift work and day work on weight gain in Japanese male workers.

METHODS AND PROCEDURES

A longitudinal cohort study was conducted in day workers (n = 4,328) and alternating shift workers (n = 2,926) of a steel company who received annual health checkups over a 14-year period between 1991 and 2005. The association between the type of job schedule and weight gain was investigated using multivariate pooled logistic regression analyses. The endpoints in the study were either a 5, 7.5, or 10% increase in BMI during the period of observation, compared to the BMI at entry.

RESULTS

The type of job schedule was significantly associated with all three BMI endpoints (5% increase in BMI; odds ratio (OR) for comparison between alternating shift workers and regular day workers, 1.14; 95% confidence interval (CI), 1.06-1.23): (7.5% increase in BMI; OR, 1.13; 95%CI, 1.03-1.24: 10% increase in BMI; OR, 1.13; 95%CI, 1.00-1.28). BMI at study entry was also positively associated with the 5, 7.5, and 10% increases in BMI during the study. On the other hand, age and drinking habits were negatively associated with 5, 7.5, and 10% increases in BMI.

DISCUSSION

Our study revealed that alternating shift work was an independent risk factor for weight gain in male Japanese workers. Efficient health screening and regular checkups, combined with support to control unhealthy lifestyle factors, would be of considerable benefit for maintaining the health of Japanese shift workers.

Elevated blood pressure, decreased heart rate variability and incomplete blood pressure recovery after a 12-hour night shift work

Shift work has been associated with increased risk of cardiovascular disease. This study was designed to determine the hemodynamic effects of 12-hour (12-h) shifts, and changes in blood pressure (BP) and heart rate variability (HRV) during 36 h rest time following 12-h shifts. Fifteen male shift workers with a mean age of 32.9 yr were recruited from a semiconductor factory. Ambulatory BP (AmBP) monitoring was performed for a total of 48 h for each participant. Six workers were monitored for 48 h by Holter electrocardiogram on both the day and night shifts. Paired self-comparison was used to estimate the difference between two hourly measurements of 12-h BP, HR, and HRV using the same timetable intra-individually. We also applied mixed models to estimate the effects of 12-h shifts on the delayed recovery of BP and heart rate (HR) in six workers who completed 96-h AmBP monitoring, including a 48-h night shift-rest period and another day shift period. Results showed that 12-h night shift work gave a persistently elevated systolic and diastolic BP (SBP and DBP) and HR, and decreased HRV compared to 12-h day shift work with the corresponding resting time. In addition, there was delayed SBP and DBP recovery on the first 12-h rest time in night shift workers, which was further demonstrated on the second 12-h rest time after adjustment for possible confounders through mixed models. In conclusion, 12-h night shift work may elevate BP and HR and decrease HRV. It is also associated with delayed BP recovery.

Shift work and its effects on the cardiovascular system

The practice of shift-work scheduling has long been part of normal work duties in emergency services such as health and security. It is only recently, in the wake of growing job opportunities and booming industries, where more employees are needed to keep services running over 24-hour periods that studies on the effects of shift work on workers' health have begun to delve deeper. The desynchronisation that occurs in circadian rhythms, with respect to sleep cycles, predisposes employees to coronary heart disease, gastrointestinal disturbances, increased risk of breast cancer and poor pregnancy outcomes. This literature review focuses on circadian rhythms, their molecular components, disturbances of these rhythms as a result of shift work and the adverse effects thereof on the cardiovascular system.

The non-cancer mortality experience of male workers at British Nuclear Fuels plc, 1946-2005

BACKGROUND

Recent studies of the Hiroshima and Nagasaki A-bomb survivors, together with some (but not all) cohorts exposed occupationally or medically to ionizing radiation, have found an increasing trend in mortality from non-malignant disease with increasing radiation dose. The aim of this study was to establish whether such a trend could be found in a large cohort of employees in the UK nuclear industry.

METHODS

The cohort comprised 64 937 individuals ever employed at the study sites between 1946 and 2002, followed up to 2005; radiation exposures as measured by personal dosimeters ('film badges') were available for 42 426 individuals classified as 'radiation workers'. Poisson regression models were used to investigate the relationship between excess mortality rates and cumulative radiation exposure, using both relative and additive risk models.

RESULTS

The cohort shows a pronounced 'healthy worker' effect. Overall, socio-economic status as indicated by employment status has a greater influence on mortality than does radiation exposure status. For male radiation workers, there is an apparent dose response for mortality from circulatory system disease [P < 0.001, ERR = 0.65 (90% CI 0.36-0.98) Sv(-1)]. However there is evidence for inhomogeneity in the apparent dose response (P = 0.016), arising principally at cumulative doses in excess of 300 mSv, when the four categories of employment and radiation exposure status are examined separately.

CONCLUSIONS

We have found evidence for an association between mortality from non-cancer causes of death, particularly circulatory system disease, and external exposure to ionizing radiation in this cohort. However, the tentative nature of biological mechanisms that might explain such an effect at low chronic doses and the above inhomogeneities in apparent dose-response, mean that the results of our analysis are not consistent with any simple causal interpretation. Further work is required to explain these inhomogeneities, and on the possible role of factors associated with socio-economic status and shift working, before any further conclusions can be drawn.

Job categories and acute ischemic heart disease: a hospital-based, case-control study in Taiwan

BACKGROUND

Most studies of the relationship between work and acute ischemic heart disease (IHD) were performed in western populations, and the extent to which their findings hold in Asian populations is largely unknown. The purpose of this study was to examine the association between job categories and non-fatal, first episodes of acute IHD in Taipei, Taiwan.

METHODS

A hospital-based, case-control design was used. Cases were patients with a first episode of non-fatal acute IHD who were admitted to the department of cardiology. Two controls without known cardiovascular disease were matched to each case for age, gender, and date of admission. A total of 119 cases and 238 controls were enrolled between April and September 2004.

RESULTS

Compared with white-collar workers, blue-collar workers had a 5.3-fold (95% CI: 1.5, 18.5) increased risk of a first episode of non-fatal acute IHD, while self-employed workers and managers/professionals had a slightly lower odds ratio of 0.6 (95% CI: 0.1, 2.4) and 0.5 (95% CI: 0.1, 2.2), respectively. Hypertension, diabetes, obesity, physical inactivity, and sleep disturbance were significant risk factors for acute IHD. A clustering of the cardiovascular risk factors was found in blue-collar workers.

CONCLUSIONS

Blue-collar workers had a 5.3-fold increased risk of a first event of non-fatal acute IHD compared with white-collar workers, and this increased risk was associated with a clustering of cardiovascular risk factors.

The triad of shift work, occupational noise, and physical workload and risk of coronary heart disease

BACKGROUND

Shift work, noise, and physical workload are very common occupational exposures and they tend to cluster in the same groups of workers.

OBJECTIVES

To study the short and long term effects of these exposures on risk of coronary heart disease (CHD) and to estimate the joint effects of these factors.

METHODS

The study population in this prospective 13 year follow up study of 1804 middle aged industrially employed men was collected at the first screening for the Helsinki Heart Study. The CHD end points (ICD-9 codes 410-414 and ICD-10 codes I20-I25) were obtained from official Finnish registers. The Finnish job-exposure matrix FINJEM provided information on occupational exposures. Relative risks (RR) of CHD for the exposures were estimated using Cox's proportional hazard models adjusting for classical risk factors of CHD.

RESULTS

The RR in the five year follow up for continuous noise combined with impulse noise was 1.28; for shift work it was 1.59, and for physical workload 1.18, while in the 13 year follow up the RRs were 1.58, 1.34, and 1.31, respectively. When adjusted for white-collar/blue-collar status the RRs decreased markedly. The RR in the 13 year follow up for those exposed to two risk factors was close to 1.7 and for those exposed to all three, 1.87.

CONCLUSION

Shift work and continuous noise entailed an excess risk for CHD in the shortest follow up with only a few retired workers but a decreasing risk during the longer follow up. For physical workload and impulse noise the trend was opposite: the CHD risk was increasing with increasing follow up time despite increasing numbers of retired workers.

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.

Dyslipidemia in Industrial Workers in Hot Environments

The aim of the study was to follow the rate and manifestation of dyslipidemia in industrial workers exposed to heat. One hundred and two male industrial workers exposed to heat and a control group of 102 male workers were studied. The microclimate components were followed and Wet Bulb Globe Temperature (WBGT) was calculated. The mean WGBT was 35.4 degrees C (28.4-41.7 degrees C) for the studied heat exposed work places. The lipid indices: total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C) and triacylglycerols were assayed with enzymatic tests. TC/HDL-C ratio was calculated, too. Arterial pressure, anthropometric variables, smoking, alcohol use were followed and no significant differences between the studied groups were found. Significantly higher TC, LDL-C and TC/HDL-C were found with the heat exposed industrial workers. Odds ratio indicated higher risk in heat exposed industrial workers of becoming dyslipidemic [for TC OR = 1.481 (1.097-2.002) and for LDL-C OR = 1.539 (1,123-2.111)]. Regular screening of lipid profile in heat exposed workers is recommended.

Cardiovascular risk in operators under radiofrequency electromagnetic radiation

The aim of the study was to assess the long-term effects of radiofrequency electromagnetic radiation (EMR) on the cardiovascular system. Two groups of exposed operators (49 broadcasting (BC) station and 61 TV station operators) and a control group of 110 radiorelay station operators, matched by sex and age, with similar job characteristics except for the radiofrequency EMR were studied. The EMR exposure was assessed and the time-weighted average (TWA) was calculated. The cardiovascular risk factors arterial pressure, lipid profile, body mass index, waist/hip ratio, smoking, and family history of cardiovascular disease were followed. The systolic and diastolic blood pressure (SBP and DBP), total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were significantly higher in the two exposed groups. It was found that the radiofrequency EMR exposure was associated with greater chance of becoming hypertensive and dyslipidemic. The stepwise multiple regression equations showed that the SBP and TWA predicted the high TC and high LDL-C, while the TC, age and abdominal obesity were predictors for high SBP and DBP. In conclusion, our data show that the radiofrequency EMR contributes to adverse effects on the cardiovascular system.

Shift workers' mortality scrutinized

The objective of this article is to reappraise previous published data on the mortality of male shift workers from Taylor and Pocock (1972). Mortality rate ratios were calculated for shift workers, ex-shift workers, and for shift workers plus ex-shift workers, respectively, compared to day workers using the Mantel-Haenszel method. The overall risk for current and former shift workers was 1.05 (95% Confidence Interval: 0.95-1.16). For ex-shift workers the mortality was increased compared to day workers (1.24, 95% Confidence Interval: 1.03-1.51). In the age specific analyses increased mortality was observed in shift workers compared with day workers in the age group of 45-54 yrs (Relative Risk: 1.47, 95% Confidence Interval: 1.12-1.93). We suggest that shift work is associated with increased mortality risk.

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.

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.

Metabolic disturbances in male workers with rotating three-shift work. Results of the WOLF study

OBJECTIVES

The aim of the present study was to investigate the relationship between important metabolic risk factors for coronary heart disease (CHD) and type 2 diabetes in shift workers and day workers.

METHODS

Cross-sectional data from a sub-population in the WOLF study consisting of 665 day workers and 659 three-shift workers in two plants were analysed.

RESULTS

A higher proportion of shift workers than day workers had high triglyceride levels (> or =1.7 mmol/l), low levels of HDL-cholesterol (<0.9 mmol/l) and abdominal obesity (waist/hip ratio>0.9). The risk of low HDL-cholesterol was doubled in shift workers, (odds ratio (OR): 2.02, 95% confidence interval (95% CI): 1.24-3.28) after being adjusted for age, socio-economic factors, physical activity, current smoking, social support and job strain. High levels of triglycerides were also significantly associated with shift work (OR: 1.40, 95% CI: 1.08-1.83). The OR for abdominal obesity was 1.19, (95% CI: 0.92-1.56). The prevalence of hyperglycaemia (serum glucose > or =7.0 mmol/l) was similar in day and shift workers. No significant interaction was seen between shift work and abdominal obesity with regard to the associations with triglycerides and HDL-cholesterol.

CONCLUSIONS

We found a significant association between shift work and lipid disturbances (i.e. low HDL-cholesterol and high triglyceride levels). We did not find any association with hyperglycaemia.

Myocardial infarction risk and occupational categories in Kaunas 25-64 year old men

AIMS

To investigate the risk of a first time myocardial infarction (MI) among different occupational categories in 25-64 year old men in Kaunas, Lithuania, a country in a transition market economy.

METHODS

Case-control study among men aged 25-64 who were residents in Kaunas between 1997 and 2000. First time, non-fatal MI cases (n = 448) were identified from the MI hospital register (International Classification of Diseases, 10th revision, code I21). Controls (n = 1777) were selected and matched on age, gender, and city district of residence. Information was obtained on occupation, smoking, hypertension, psychosocial, and behavioural factors. The International Standard Classification of Occupations (ISCO) was used to code for occupational categories. The relation between MI and occupational categories was evaluated by logistic regression analysis, adjusting for a number of selected risk factors.

RESULTS

Legislators, senior officials, and managers (1st ISCO category) had a twofold increased risk for MI compared to craft and related trades workers (7th ISCO category) after adjustment for age, district, smoking, hypertension, obesity, stress, education, and employment duration. An increased risk for professionals (2nd ISCO category) and plant and machine operators and assemblers (8th ISCO category) was also observed. Employment duration in the last occupation for 20 years and more almost doubled the risk of MI in the whole population. We also found an increased risk for other traditional IHD risk factors such as smoking and arterial hypertension.

CONCLUSIONS

Differences in first time MI risk among occupational categories were found. Legislators, senior officials, and managers (1st ISCO category), professionals (2nd ISCO category), and plant and machine operators and assemblers (8th ISCO category) were at an increased risk. Differences in psychosocial factors in transition market economy countries may contribute to observed results.

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.

Circadian rhythm, shift work, and emergency medicine

Human beings, like other living organisms, have physiologic systems that are cyclic in nature. Many of these systems have a circadian length. This provides for internal stability while at the same time enabling the organism to interact with the external environment and respond to changes in that environment. These physiologic systems, including those with a circadian length, can change timing as a result of environmental cues, such as the light-dark cycle or seasonal variations, but this takes time. When people engage in rotating or night shift work, the circadian rhythms are unable to quickly adapt to a rapidly changing activity schedule. This results in desynchronosis of many physiologic systems, including those with circadian timing. Because many emergency physicians engage in shift work, they are subject to the effects of circadian rhythm disruption. Research on the effect of desynchronosis on emergency physicians is sparse but has demonstrated negative effects. This article reviews the effect of desynchronosis on the health and productivity of physicians engaged in shift work.