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

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

Changes in frequency of premature complexes and heart rate variability related to shift work

OBJECTIVES—To investigate whether an increased risk of cardiovascular disease might be caused by increased arrhythmogeneity and by unfavourable changes in autonomic cardiac control the changes in the occurrence of premature complexes (PVCs) and in heart rate variability (HRV) were studied in subjects who started to work in shifts.
METHODS—1 Year changes in frequency of PVCs and HRV were measured in 49 shift workers and 22 control subjects working in daytime. All respondents were starting in a new job in integrated circuit or waste incinerator plants.
RESULTS—The incidence of PVC increased significantly in shift workers over the 1 year follow up, compared with daytime workers. The frequency of ventricular extrasystoles increased in 48.9% of the shift workers, and in 27.3% of the daytime workers. The Spearman correlation coefficient between the number of nights worked and the change in PVCs was 0.33 (p=0.004). A small non-significant unfavourable change in HRV was found in both the shift and daytime workers.
CONCLUSIONS—A change in arrhythmogeneity, but not in cardiac autonomic control, might explain the increased risk of cardiovascular disease in shift workers.


Keywords: arrhythmia; heart rate; shift work     

倒班作业对工人激素水平的影响

采用整群抽样,选取某电子企业281名倒班员工作为倒班组,211名常白班员工作为对照组,通过调查问卷、体格检查方式调查激素水平变化。结果显示,在调整年龄、性别、吸烟、饮酒、体质指数(BMI)等混杂因素后,倒班组睾酮(T)、褪黑素(MT)、胰岛素(Ins)水平均低于对照组,差异有统计学意义(P0.05)。提示倒班作业对人体T、MT、Ins水平均有影响。     

Heart rate during work and heart rate variability during the following night: a day-by-day investigation on the physical activity paradox among blue-collar workers

Objectives:Contrary to leisure-time physical activity, occupational physical activity (OPA) may have harmful health effects, called the physical activity paradox. A proposed mechanism is that OPA can elevate the heart rate (HR) for several hours per day. We aimed to investigate the association between the mean intensity of OPA and HR variability (HRV) indices the following night.Methods:Three cohorts (NOMAD, DPhacto, and Physical Workload and Fitness) involving blue-collar workers from different sectors were merged in this study. HR monitors (Actiheart) recorded 24-hour inter-beat intervals (IBI) for up to four consecutive days. The relative intensity of the mean HR during work was estimated by HR reserve (%HRR), and time-domain indices of HRV were analyzed during the following night. Data were analyzed using a multilevel growth model to test the association between mean %HRR during work and HRV indices at night in a day-by-day analysis adjusted for age, BMI, alcohol consumption, smoking, and occupation.Results:The dataset included a sample of 878 Danish blue-collar workers, with a mean %HRR during work of 31%, and 42% worked at an intensity ≥30%HRR. The multilevel model showed negative within- and between-subject associations between %HRR during work and HRV indices at night.Conclusions:Our results indicate a higher %HRR during work to associate with lower HRV indices the following night and a higher HR, reflecting an imbalanced autonomic cardiac modulation. This finding supports a high mean HR during work to be a potential underlying mechanism for the harmful health effect of OPA.     

Problems related to shift work. A field study of Swedish railroad workers with irregular work hours.

A group of 132 engineers from the north of Sweden was included in the study. A subsample of about 50 subjects was selected for further laboratory investigations during a light and warm summer period and a dark and cold winter period. The mean for the hours of sleep noted on the sleep records was significantly lower for night work than for day work. The amount of sleep during night work was significantly less during the light period than during the dark period as was the amount of sleep during the day off. Body temperature measured during work followed a daytime pattern and had a low amplitude. Potassium excretion and the blood levels of cortisol displayed a stable circadian rhythm with a daytime pattern. Many environmental factors made the results of catecholamine data difficult to interpret. The frequency of reported peptic ulcers was higher in the engineer group than in some other groups.     

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

Objectives: There is evidence that shift work contributes to excess cardiovascular mortality. The purpose of this study was to determine the effects of shift work on heart rate-corrected QT (QTc) and blood pressure in relation to heart rate variability (CV_RR). Methods: The study population consisted of 153 male shiftworkers and 87 male day workers who were employed at a copper-smelting plant. The QTc interval, total power spectral density (t-PSD) of 100 RR intervals, PSDs with frequencies of 0.01 Hz–0.15 Hz and 0.15 Hz–0.40 Hz (PSD_LF and PSD_HF), CV_RR, low frequency (LF) component variability and high frequency (HF) component variability (CCV_LF and CCV_HF) and %LF (PSD_LF/(PSD_LF+PSD_HF) ·100) were measured (LF and HF components are thought to reflect the sympathetic and parasympathetic activities, respectively). Results: The QTc interval was significantly longer in the shiftworkers than in the day workers, although there was no significant difference in systolic or diastolic blood pressure between the two groups. Also, the CCV_LF and log(PSD_LF) were significantly depressed in the shiftworkers. In the day workers, the QTc interval was significantly related to the CV_RR, log(t-PSD), CCV_HF, log(PSD_HF),%LF, and log(LF/HF ratio) (partial correlation coefficient r=–0.305, –0.377, –0.312, –0.355, 0.297, and 0.277, respectively). In the shiftworkers only two relations of the QTc interval to non-specific CV_RR and log(t-PSD) were significant. Conclusion: The clear association between long QTc interval and reduced parasympathetic activity observed in the day workers did not exist in the shiftworkers. Rather, the shiftworkers had a selective reduction in sympathetic drive, which may have compensated for prolonged QTc interval due to shift work. On the other hand, the impact of shift work on hypertension remains unclear, although reduced sympathetic drive in the shiftworkers may explain the absence of differences in blood pressure between shiftworkers and day workers to some extent.     

倒班作业对石油化工企业员工睡眠质量的影响

采用整群抽样选择2 568名某石油化工企业员工为研究对象,采用匹兹堡睡眠质量指数量表(PSQI)分析倒班对睡眠质量的影响。结果显示,倒班组在主观睡眠质量、睡眠效率、睡眠障碍和日间功能障碍等得分均比非倒班组高(P0.05)。倒班是罹患睡眠障碍危险因素(OR=2.15,95%CI:1.66～2.80);后夜班者罹患睡眠障碍风险比前夜班者高(P0.05);随着倒班频次、年限增加,罹患睡眠障碍的风险随之增加。     

倒班对男性钢铁工人超重/肥胖的影响

目的 探讨倒班对钢铁工人超重/肥胖的影响。方法 对2015年3月至2016年3月进行职业健康查体的唐山钢铁集团有限责任公司男性在职员工进行问卷调查和体格测量。采用logistic回归模型和限制性立方样条模型,分析倒班及倒班年限对钢铁工人超重/肥胖的影响。结果 共纳入7 262例男性钢铁工人,超重/肥胖率为64.5%（4 686/7 262）,其中超重率为34.3%,肥胖率为30.2%。调整年龄、文化程度、家庭人均月收入等因素后,多因素logistic回归分析结果显示,现在倒班与超重/肥胖、肥胖有关,OR值（95%CI）分别是1.19（1.05～1.35）、1.15（1.00～1.32）。限制性立方样条模型分析显示,男性工人中倒班年限与超重/肥胖具有相关性（χ²=8.91,P<0.05）且呈非线性关系（非线性检验χ²=7.43,P<0.05）。倒班年限与肥胖具有相关性（χ²=15.95,P<0.05）且呈非线性关系（非线性检验χ²=10.48,P<0.05）。结论 男性钢铁工人倒班与超重/肥胖有关,且倒班年限与超重/肥胖呈非线性关系。     

Behavior of blood pressure in 3 shift work of workers with level I WHO hypertension

Blood pressure tests were carried out on 40 shift workers with a hypertension level of 1 (according to WHO). Every 5 day period these tests were carried out before, during and after work in the early, late and night shifts. No significant change of both the systolic and the diastolic blood pressure could be found, which could result from shift work, before and after each shift irrespective of the blood pressure stabilization (good, satisfactory, unsatisfactory). The group containing satisfactorily as well as unsatisfactorily stabilized workers suffering from hypertension showed a significant decrease of the systolic blood pressure from the early shift through the late till the night shifts, with the diastolic blood pressure remaining constant. There were no apparent differences in the range of average blood pressure values regarding the various forms of treatment (without medication, monotherapy and combined therapy). The systolic blood pressure is significantly lower only in the group with no medication in the early shift after finishing work and it also decreases from the early shift through the late till the night shifts, while within the other therapy groups no change of both the systolic and the diastolic blood pressure was apparent. Thus shift work does not cause any measurable increase in blood pressure within the test group (suffering from hypertension) that would impair their working capacity. There is no increase of health risk with regard to the blood pressure response during shift work particularly during night work provided the blood pressure is within the normal range.     

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.     

Effect of long work hours and shift work on high-sensitivity C-reactive protein levels among Korean workers

Objective:We aimed to investigate the association between low-grade inflammation as indicated by high-­sensitivity C-reactive protein (hsCRP) level and organizational factors, such as work hours and shift work.Methods:We evaluated 7470 young and middle-aged workers who participated in the Korea National Health and Nutrition Examination Surveys from 2015–2018. Work hours were determined from self-reported questionnaires. Shift work was defined as a non-daytime fixed work schedule. An interaction effect between shift work and long work hours on the hsCRP level was estimated using relative excess risk due to interaction (RERI) and attributable proportion (AP) with 95% confidence intervals (CI).Results:Increased hsCRP levels were prevalent in 25.2% of the study population. There was a significant association between long work hours and increased hsCRP, especially among middle-aged men [odds ratio (OR) 1.50 (95% CI 1.20–1.87) for moderately increased hsCRP and OR 1.62 (95% CI 1.14–2.30) for highly increased hsCRP]. There was a significant interaction effect between long work hours and shift work on increased hsCRP among middle-aged workers. The RERI were 0.03 (95% CI 0.02–0.04) and 0.56 (95% CI 0.45–0.68) among middle-aged men and women, respectively. The AP were 0.02 (95% CI 0.01–0.03) and 0.36 (95% CI 0.31–0.40) among middle-aged men and women, respectively.Conclusions:There was no significant association between shift work and the level of hsCRP. Long work hours were related to low-grade inflammatory processes, but only in middle-aged workers. There was an interaction effect between long work hours and shift work for increased hsCRP, especially in middle-aged women.     

The relationship between shift work and the onset of hypertension in male Japanese workers

We assessed the effect of shift work on the onset of hypertension. The design of this study was that of a cohort study from 1991-2001. In sum, 5338 workers comprised this cohort. The event was the onset of hypertension (systolic blood pressure >or=140 mm Hg and/or diastolic blood pressure >or=90 mm Hg and/or medication). Pooled logistic regression analysis was performed, including job schedule type, age, body mass index, lifestyle, and the results of blood chemistries as covariates. The odds ratio of the onset of hypertension in shift workers for daytime workers was 1.10 and significant. Our study revealed that shift work independently affected the onset of hypertension, and suggested that shift work is a risk factor for the onset of hypertension.