Shiftwork and mortality from ischaemic heart disease

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.

Past Shift Work and Incident Coronary Heart Disease in Retired Workers: A Prospective Cohort Study

Present shift work has been associated with coronary heart disease (CHD) among employed workers, but it remains unclear whether shift work performed in the past is still associated with CHD in retired workers. We recruited 21,802 retired workers in Shiyan, China, in 2008-2010 and 2013 and followed them for CHD events occurring up to December 31, 2018. Retired workers with longer durations of past shift work (rounded to 0.25 years) had higher CHD risks (for those with ≤5.00, 5.25-10.00, 10.50-20.00, and >20.00 years of past shift work, hazard ratios were 1.05 (95% confidence interval (CI): 0.94, 1.16), 1.08 (95% CI: 0.94, 1.25), 1.23 (95% CI: 1.07, 1.42), and 1.28 (95% CI: 1.08, 1.51), respectively). The association was substantially higher among service or sales workers than among manufacturing or manual-labor workers (for every 5-year increase in past shift work, hazard ratio = 1.11 (95% CI: 1.05, 1.16) vs. hazard ratio = 1.02 (95% CI: 0.98, 1.06)). Moreover, the risk was lower among those who were physically active than among their inactive counterparts (P for interaction = 0.019). Longer duration of past shift work was associated with higher risk of incident CHD among these retired workers, especially those from the service or sales sectors. Physical exercise might be beneficial in reducing the excess risk.

Quantitative Bias Analysis of the Association between Occupational Radiation Exposure and Ischemic Heart Disease Mortality in UK Nuclear Workers

The scientific question of whether protracted low-dose or low-dose-rate exposure to external radiation is causally related to the risk of circulatory disease continues to be an important issue for radiation protection. Previous analyses of a matched case-control dataset nested in a large cohort of UK nuclear fuel cycle workers indicated that there was little evidence that observed associations between external radiation dose and ischemic heart disease (IHD) mortality risk [OR = 1.35 (95% CI: 0.99-184) for 15-year-lagged exposure] could alternatively be explained by confounding from pre-employment tobacco smoking, BMI or blood pressure, or from socioeconomic status or occupational exposure to excessive noise or shiftwork. To improve causal inference about the observed external radiation dose and IHD mortality association, we estimated the potential magnitude and direction of non-random errors, incorporated sensitivity analyses and simulated bias effects under plausible scenarios. We conducted quantitative bias analyses of plausible scenarios based on 1,000 Monte Carlo samples to explore the impact of exposure measurement error, missing information on tobacco smoking, and unmeasured confounding, and assessed whether observed associations were reliant on the inclusion of specific matched pairs using bootstrapping with 10% of matched pairs randomly excluded in 1,000 samples. We further explored the plausibility that having been monitored for internal exposure, which was an important confounding factor in the case-control analysis for which models were adjusted, was indeed a confounding factor or whether it might have been the result of some form of selection bias. Consistent with the broader epidemiological evidence-base, these analyses provide further evidence that the dose-response association between cumulative external radiation exposure and IHD mortality is non-linear in that it has a linear shape plateauing at an excess risk of 43% (95% CI: 7-92%) on reaching 390 mSv. Analyses of plausible scenarios of patterns of missing data for tobacco smoking at start of employment indicated that this resulted in relatively little bias towards the null in the original analysis. An unmeasured confounder would have had to have been highly correlated (rp > 0.60) with cumulative external radiation dose to importantly bias observed associations. The confounding effect of "having been monitored for internal dose" was unlikely to have been a true confounder in a biological sense, but instead may have been some unknown factor related to differences over time and between sites in selection criteria for internal monitoring, possibly resulting in collider bias. Plausible patterns of exposure measurement error negatively biased associations regardless of the modeled scenario, but did not importantly change the shape of the observed dose-response associations. These analyses provide additional support for the hypothesis that the observed association between external radiation exposure and IHD mortality may be causal.

Healthy Diet and Reduction of Chronic Disease Risks of Night Shift Workers

BACKGROUND

The large increase in epidemiological studies on night shift work is due to the important effects of night shift work on workers' health and psychophysical wellbeing. The short-term effects-insomnia, difficulties in managing work and private life, lower work performance, and more work and extra-work accidents-are easily studied. However, there are several long-term effects that are difficult to study because of the need for detailed exposure assessment and the long latency periods of these diseases.

OBJECTIVE

The aim was to collect epidemiologic evidence of diseases in night shift workers, describing their biological pathways and a set of dietary guidelines.

METHODS

This is a review on diet and health effects in night shift workers.

RESULTS

Significant increases in the rate ratios and hazard ratios of different diseases were associated with modified eating behaviours and poor eating habits among night shift workers. Night shift work is a risk factor for disruption of the circadian rhythms and for some genetic deregulation because it produces the inversion of the sleep/wake cycle and modifies the alternation between activity and rest.

CONCLUSION

A healthy diet and improved dietary practices, together with other factors, can reduce shift workers' chronic disease risk. The literature showed the importance of eating behaviour in order to prevent diseases in these workers; therefore, educational programmes are necessary to encourage several important lifestyle changes. The target of our future research will be the role of food components in some dietetic habits for the prevention of disease in night shift workers.

Shift work and risk of cardiovascular disease morbidity and mortality: A dose–response meta-analysis of cohort studies

Background

Previous studies have suggested that shift work is associated with a higher risk of cardiovascular disease. However, the quantitative dose–response relationship between duration of shift work and cardiovascular disease risk is still unknown. We aimed to evaluate the dose–response association between duration of shift work and risk of cardiovascular disease morbidity and mortality.

Design

A systematic review and meta-analysis.

Methods

PubMed and Embase were searched from inception to 1 December 2017. Prospective cohort studies that reported the associations between duration of shift work and cardiovascular disease risk with at least three categories were included. Data were pooled by using fixed or random effect models. The continuous dose–response associations were assessed by using fixed effect restricted cubic splines with four knots.

Results

Five prospective cohort studies with 10 reports were included. No evidence of a curvilinear association was observed between duration of shift work and risk of cardiovascular disease, similar findings were observed in cardiovascular disease morbidity and mortality. The summary relative risk (RR) of an increase of 5 years of shift work was 1.05 (1.04–1.07) with moderate heterogeneity ( P = 0.142, I2 = 33.2%) for cardiovascular disease, 1.06 (1.04–1.08) with low heterogeneity ( P = 0.279, I2 = 21.7%) for cardiovascular disease morbidity, and 1.04 (1.02–1.06) with moderate heterogeneity ( P = 0.135, I2 = 38.5%) for cardiovascular disease mortality, respectively.

Conclusions

Shift work could probably increase the risk of cardiovascular disease and cardiovascular disease mortality in a dose–response way. These findings could have implications for guideline recommendations regarding the risk related to shift schedules.

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.

Multicenter historical cohort study of the relationship between shift work and blood pressure

BACKGROUND

Regarding the relationship between blood pressure (BP) and shift work (SW), previous studies have reported contradictory results. In the present study, we used Bayesian multilevel modeling to evaluate the association of SW and BP after controlling some confounding factors.

METHODS

Data of this multicenter historical study were extracted from annual observations of the male workers of Isfahan's Mobarakeh Steel Company (IMSC) and Polyacryl Iran Corporation (PIC) in Isfahan, Iran, between 2003 and 2011. In this research, we assessed the effect of SW on systolic BP (SBP) and diastolic BP (DPB) with controlling body mass index, age, work experience, marriage, and education status.

RESULTS

A total of 8613 (IMSC, n = 5314 and PIC, n = 3299) workers participated in this study with a mean [standard deviation (SD)] age of 41.60 (8.30) and mean (SD) work experience of 16.17 (7.89) years. In this study, after controlling confounding factors, we found no significant relationship between SW and SBP and DBP.

CONCLUSION

In general, the results of this multicenter cohort study did not support a relationship between SW and BP. We suggest prospective studies with controlling more confounding factors in this area.

Historical cohort study of shift work and blood pressure

BACKGROUND

It has been suggested that shift work (SW) is associated with changes in blood pressure (BP). However, studies have reported contradictory results.

AIMS

To prospectively examine the association between SW and BP among male workers.

METHODS

A historical cohort study, involving workers of Esfahan's Mobarakeh Steel Company, in Iran, was conducted over 14 years. The association between SW, systolic BP (SBP) and diastolic BP (DBP) was investigated after adjusting for body mass index, age, work experience, marriage, smoking and education based on the Bayesian multilevel modelling approach.

RESULTS

The study sample included 5331 male workers. The mean age (standard deviation, SD) was 34.8 (6.6) years and mean work (SD) experience was 9.4 (6.1) years. Among these subjects, 2348 (44%), 340 (6%) and 2643 (50%) were day workers, weekly rotating shift workers and routinely rotating shift workers, respectively. The mean SBP (SD) and DBP (SD) of these workers were 118.7 (8.1) and 73.1 (6.7) mmHg, respectively. After controlling for several confounding variables, there was no significant relationship between SBP and DBP and SW.

CONCLUSIONS

No significant association between SW and BP was observed among these three groups (day workers, weekly rotating shift workers and routinely rotating shift workers). Prospective studies, which control for confounding factors, such as the healthy worker effect, occupational history, family history and psychological factors (e.g. occupational stress and job satisfaction), are required to evaluate this further.

A retrospective cohort study on factors associated blood pressure using multilevel modeling

BACKGROUND

Hypertension is a health problem in Iran. Given the importance of this subject, we reviewed the factors affecting the blood pressure in this survey.

METHODS

This retrospective cohort study was performed on 3961 male workers employed at Isfahan Polyacryl Corporation (Iran) in health and safety executive between 1996 until 2008. In this study, systolic and diastolic blood pressure (SBP and DBP) were considered as dependent variables; body mass index (BMI), age, type of job, marital status, shift work and educational level were considered as independent variables. MLwiN programmer version 2.1 was used to analyze the data.

RESULTS

BMI, age, shift work, marital status and educational level had statistical significant association with DBP. The result for SBP was similar to DBP except shift work and educational level that had no statistically significant association.

CONCLUSION

The results can be considered in the industry to provide practical solutions to reduce blood pressure.

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.

Effects of lifetime exposure to shiftwork on fitness for duty in police officers

Aging and demographic changes in Europe and other global economies have led to a discussion about postponing the legal retirement age; however, health and safety consequences for the workforce have not yet been examined. Thus, the aim of this study was to investigate the effects of lifetime exposure to shiftwork on health impairments and fitness for duty. Two samples of the police force from one of the states of the Federal Republic of Germany were used. One sample was collected in 2008-2009 with a self-administered Internet questionnaire (n = 705); the other sample was derived from employment records provided by the police force of the same federal state for the years 2002-2009 (n = 2460). Both samples contained information about the number of years worked in shiftwork across the entire working life and impairments to fitness for duty assessed by occupational physicians. Thus, the number of years of shiftwork until the diagnosis of the first reduction in fitness for duty could be calculated. Survival analyses were performed to estimate the risk (hazard rate) for experiencing a reduction in fitness for duty across lifetime exposure to shiftwork in years, controlling for age, sex, work type, and police district. Hazard estimates were compared across both samples to cross-validate the results. The findings indicated an increase in the risk of reduced fitness for duty with increasing number of years in shiftwork during the working life in both samples. The hazard rates followed an exponential trend, indicating a rapid increase in health impairments in particular beyond 20 yrs of shiftwork. These findings were consistent in both samples, collected with different methods and over different time periods, thus indicating high validity. Therefore, occupational stress factors, such as exposure to shiftwork, need to be taken into account when discussing the postponement of the legal retirement age.

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.

Unaltered instrumental learning and attenuated body-weight gain in rats during non-rotating simulated shiftwork

Exposure to shiftwork has been associated with multiple health disorders and cognitive impairments in humans. We tested if we could replicate metabolic and cognitive consequences of shiftwork, as reported in humans, in a rat model comparable to 5 wks of non-rotating night shifts. The following hypotheses were addressed: (i) shiftwork enhances body-weight gain, which would indicate metabolic effects; and (ii) shiftwork negatively affects learning of a simple goal-directed behavior, i.e., the association of lever pressing with food reward (instrumental learning), which would indicate cognitive effects. We used a novel method of forced locomotion to model work during the animals' normal resting period. We first show that Wistar rats, indeed, are active throughout a shiftwork protocol. In contrast with previous findings, the shiftwork protocol attenuated the normal weight gain to 76 ± 8 g in 5 wks as compared to 123 ± 15 g in the control group. The discrepancy with previous work may be explained by the concurrent observation that with our shiftwork protocol rats did not adjust their between-work circadian activity pattern. They maintained a normal level of activity during the "off-work" periods. In the control experiment, rats were kept active during the dark period, normally dominated by activity. This demonstrated that forced activity, per se, did not affect body-weight gain (mean ± SEM: 85 ± 11 g over 5 wks as compared to 84 ± 11 g in the control group). Rats were trained on an instrumental learning paradigm during the fifth week of the protocol. All groups showed equivalent increases in lever pressing from the first (3.8 ± .7) to the sixth (21.3 ± 2.4) session, and needed a similar amount of sessions (5.1 ± .3) to reach a learning criterion (≥ 27 out of 30 lever presses). These results suggest that while on prolonged non-rotating shiftwork, not fully reversing the circadian rhythm might actually be beneficial to prevent body-weight gain and cognitive impairments.

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

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

Bypassing the selection rule in choosing controls for a case-control study

OBJECTIVES

It has been argued that in case-control studies, controls should be drawn from the base population that gives rise to the cases. In designing a study of occupational injury and risks arising from long-term illness and prescribed medication, we lacked data on subjects' occupation, without which employed cases (typically in manual occupations) would be compared with controls from the general population, including the unemployed and a higher proportion of white-collar professions. Collecting the missing data on occupation would be costly. We estimated the potential for bias if the selection rule were ignored.

METHODS

We obtained published estimates of the frequencies of several exposures of interest (diabetes, mental health problems, asthma, coronary heart disease) in the general population, and of the relative risks of these diseases in unemployed versus employed individuals and in manual versus non-manual occupations. From these we computed the degree of over- or underestimation of exposure frequencies and exposure ORs if controls were selected from the general population.

RESULTS

The potential bias in the OR was estimated as likely to fall between an underestimation of 14% and an overestimation of 36.7% (95th centiles). In fewer than 6% of simulations did the error exceed 30%, and in none did it reach 50%.

CONCLUSIONS

For the purposes of this study, in which we were interested only in substantial increases in risk, the potential for selection bias was judged acceptable. The rule that controls should come from the same base population as cases can justifiably be broken, at least in some circumstances.

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.

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.

Cardiovascular reaction to job stress in middle-aged train drivers

In this study, cardiovascular (CV) response to a standard laboratory challenge was compared to 24-hr noninvasive monitoring of heart rate (HR) and blood pressure (BP) in 30 healthy middle-aged train drivers. Laboratory stress test consisted of the orthostatic test, the cold pressor test, the Valsalva maneuver, the Stroop test, and the numerical square. In addition, the participants completed an extensive questionnaire on their health state and family health history, lifestyle, job stress, social and family support, personality characteristics, and health risk behaviors. In waking activities (leisure time, traveling lo work, preparations for driving, and an uneventful driving) NR and systolic blood pressure (SBP), hut not diastolic blood pressure (DBP), were normal (e.g., mean HR = 78.3, SBP = 128.6, and DBP = 92.3 during driving). In occasional stressful work situations, most participants reacted with a considerable rise in SBP and DBP (maximum values 201 for SBP and 126 for DBP). Interindividual differences in maximum BP reactions to emergency stress were predicted reliably by several psychological characteristics and by the CV reactions to the laboratory psychological challenge. The frequency, intensity, and persistence of psychological and physiological reactions to urgent situations appear to be more relevant measures of the health impact of psychological job stress than are the shift average values of physiological stress markers.

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.

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.

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.

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.

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.