Experimental Studies
Work-Related Psychosocial Hazards and Arteriosclerosis A Cross-Sectional Study Among Medical Employees in a Regional Hospital in Taiwan Li-Ping Chou,1,2 MD, Chung-Yi Li,2,3 PhD, and Susan C. Hu,2 PhD Summary The association of psychosocial stress with cardiovascular disease (CVD) is still inconclusive. The aim of this study was to examine the relationships between arteriosclerosis and various work-related conditions among medical employees with various job titles. A total of 576 medical employees of a regional hospital in Taiwan with a mean age of 43 years and female gender dominance (85%) were enrolled. Arteriosclerosis was evaluated by brachial-ankle pulse wave velocity (baPWV). Workrelated conditions included job demands, job control, social support, shift work, work hours, sleep duration, and mental health. The crude relationship between each of the selected covariates and baPWV was indicated by Spearman correlation coefficients. A multiple linear regression model was further employed to estimate the adjusted associations of selected covariates with arteriosclerosis. The mean baPWV of participants was 11.4 ± 2.2 m/s, with the value for males being significantly higher than that for females. The baPWV was associated with gender, age, medical profession, work hours, work type, depression, body mass index, systolic and diastolic blood pressures, fasting glucose, and cholesterol. After being fully adjusted by these factors, only sleep duration of less than 6 hours and weekly work hours longer than 60 hours were significantly associated with increased risk of arteriosclerosis. The conditions of job demands, job control, social support, shift work, and depression showed no significant association with baPWV. Longer work hours and shorter sleep durations were associated with an increased risk of arteriosclerosis. These findings should make it easier for the employer or government to stipulate rational work hours in order to avoid the development of cardiovascular disease among their employees. (Int Heart J 2015; 56: 644-650) Key words: Pulse wave velocity, Cardiovascular disease, Stress
C
ardiovascular disease (CVD) is the leading cause of death in most industrialized nations. Multiple risk factors predispose people to the progression of CVD. By controlling these risk factors, the incidence and mortality rate of CVD has been reduced in several industrialized countries in recent decades.1-3) Among these risk factors, psychosocial stress is noted as a widespread phenomenon and plague of modern society. One large-scale and world-wide case control study revealed psychosocial stress was correlated to a 2.67-fold increased risk of acute myocardial infarction, which is a more dangerous condition than that of hypertension and diabetes.4) Many work-related psychosocial stressors are associated with CVD. Karosak, et al commenced pioneering work and developed the dominant demand-control model (DCM) approximately 3 decades ago to study work-related stress.5) Work characteristics of low decision latitude and high work load will result in high job strain. Job strain will increase the risk of incident coronary heart dis-
ease by 23% compared to no job strain in large pooled data.6) Recently, long work hours, 7-10) shift work, 11) short sleep hours,12,13) and depression 14) were also considered to be emerging work-related hazards leading to CVD. Despite the enormous number of papers that have explored the association between job stress and CVD over the last 3 decades, the results are heterogeneous.6,15) Most of these studies come from observational data and nearly half of the results are negative or even in inverse relation between job stress and CVD. There are several inherent methodological limitations in these studies. One of the most important reasons is that the causality between the exposure of stress and the outcome of CVD is a long process and difficult to confirm because atherosclerosis is a pivotal pathological mechanism of CVD and it always progresses very slowly.16) Thus, recently research efforts have focused on the subclinical change of CVD including carotid intima-media thickness,17,18) coronary calcium score,19) and arterial stiffness 20,21) as the study surrogate end-
From the 1 Division of Cardiology, Department of Medicine, Sin-Lau Hospital, 2 Department of Public Health, College of Medicine, National Cheng Kung University, Tainan, and 3 Department of Public Health, College of Public Health, China Medical University, Taichung, Taiwan. Address for correspondence: Susan C. Hu, PhD, Department of Public Health, College of Medicine, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan. E-mail: [email protected] Received for publication April 4, 2015. Revised and accepted May 1, 2015. Released in advance online on J-STAGE November 9, 2015. All rights reserved by the International Heart Journal Association. 644
Vol 56 No 6
PSYCHOSOCIAL HAZARDS AND ARTERIOSCLEROSIS
point. Arteriosclerosis reflects the fibrotic change and poor compliance of arterial vessels, which represents vascular damage and becomes an independent risk factor of CVD.22) There are several methods to measure arterial stiffness, among which pulse wave velocity (PWV) is a simple and noninvasive measurement that has become a popular screening method in recent years.23) Brachial-ankle PWV (baPWV) is a newly developed method which is less time-consuming and less skill-dependant.24) The baPWV method is associated with age, gender, risk factors of CVD, and Framingham risk score, and has been shown to be a good independent predictor of coronary artery disease.25-29) One recent meta-analysis, which collected 18 prospective cohort studies with a total of 8,169 participants and a mean follow-up of 3.6 years, revealed baPWV can predict total cardiovascular events, cardiovascular mortality, and all-cause mortality. The pooled relative risks were 2.95 (95% CI, 1.635.33), 5.36 (95% CI, 2.17-13.27), and 2.45 (95% CI, 1.563.86), respectively.30) The value of baPWV indicates the severity of arteriosclerosis, which is considered to be an early marker of atherosclerosis and is related to later cardiovascular disease. It is anticipated that measuring baPWV and adjusting the potential risk factors of CVD may enable us to clarify the mechanism of occupational hazards and CVD. Only two studies have explored the association between psychosocial stress and arteriosclerosis evaluated by baPWV. Both of these studies came from Japanese subjects.20,21) In addition, these papers only used Karasek’s demand control model and/or Siegrist’s effort reward imbalance model as their independent factors. However, many other work-related hazards including long work hours, shift work, short sleep duration, and psychological problems may also relate to CVD, but have never been studied. To the best of our knowledge, there has never been such a report in Taiwanese employees, especially those who work in hospitals. The aim of this study was to examine the relationship between multiple work-related hazards and arteriosclerosis among medical employees in Taiwan.
Methods Participants and study design: A cross-sectional study design was used. The volunteer participants were recruited from a regional hospital in Tainan, Taiwan. The hospital had 1,490 hospital employees including 150 physicians, 600 nurses, and 740 other medical employees. In May 2013, the hospital administrators conducted a social epidemiologic survey to explore the job-related stressors and health conditions among the employees before the implementation of health-promotion programs. There were 1,329 medical employees who completed the electronic questionnaire (response rate of 89%). Among them, 676 volunteers were measured for arteriosclerosis. We then defined that the valid blood sampling period for glucose and cholesterol should be within 6 months. Finally, 576 professionals were selected as subjects. This study was approved by the Ethics Review Board of Sin Lau Hospital (SLH-919-104-01). Measurement of arteriosclerosis: Arteriosclerosis was measured by non-invasive methods with an automatic waveform analyzer (VaSera VS-1000, Fukuda Denshi, Japan). The measurement of arterial stiffness was performed between 12:00 and 14:00 pm by experienced technicians. The participant laid on a
645
bed for at least 5 minutes, and then the cuffs were wrapped on both sides of their brachia and ankles together. To obtain baPWV, pulse volume wave forms of the brachial and tibia arteries were recorded simultaneously. Path lengths from the heart to the ankle and from the heart to the brachium were marked as La and Lb. La-Lb represents the distance between brachium to ankle and was calculated using the following formula: La-Lb = 0.59 x body height (cm) + 14.4 (modified from Kitahara, et al).31) The time interval between the brachium and ankle is expressed as ΔTab. The baPWV was then calculated as follows: baPWV = (La-Lb)/ΔTab. The higher the value of baPWV, the greater the severity of the arteriosclerosis. In this study, we selected the higher of the right- or left-sided baPWV for our analyses. Socio-demographics, work characteristics: The self-administered questionnaire used included socio-demographic information and work characteristics. Socio-demographic information consisted of gender, age, educational level, marital status, and medical profession. Work characteristics included work hours, work type, and sleep hours. Work hours were calculated as average work hours per week in the previous month, and were classified as ≦ 40 hours, 41-49 hours, 50-59 hours, and ≧ 60 hours. Work type included fixed day work, fixed night work, and shift work. Sleep hours were categorized as < 6 hours, 6-8 hours, and > 8 hours in everyday sleep. Measurement of job stress: A Chinese version of the Job Content Questionnaire (C-JCQ) was chosen to measure job strain. C-JCQ is derived from the Karasek Demand-Control-Support model and has been validated and used with success in Taiwanese subjects.32,33) Job demands, mean work load, and job control represent decision latitude. As in Karasek’s model, work that possesses the characteristics of high job demand and low job control resulted in high job strain, which, in turn, creates the highest risk of CVD. Social support was an effect modifier and was later added in the domain of the demand control model. Therefore, C-JCQ consisted of 3 subscales: 9 questions on job demands, 8 questions on job control, and 8 questions on social support. Each question was measured on a 4-point scale. The scores of job demands and control were calculated separately and divided into tertiles to indicate high, medium, and low in this study. The scores of social support were expressed as high (score ≧ 24) and low (score < 24). Detailed descriptions of the C-JCQ can be found in a previously published paper.34) Measurement of mental health: Because the way of emotional expressions varies with culture, we used the “Taiwanese Depression Questionnaire” (TDQ) to screen the prevalence of depression in our study participants. The 18-item TDQ had a sensitivity and specificity of 0.89 and 0.92, respectively, at the cutoff score of 19. It was superior to the Beck Depression Inventory in detecting depressive patients in Taiwan.35,36) Thus, for this study we selected a cut-off point score of ≧ 19 to indicate the presence of depression. Cardiovascular risk factor survey: Cardiovascular risk factors included smoking status, body mass index (BMI), fasting glucose, total cholesterol, and hypertension, all of which were obtained from the employees’ health profiles. Smoking status was classified as “current/or ex-smoker” or “never.” The BMI was measured as body weight in kilograms divided by the square of body height in meters (kg/m2). Standard laboratory techniques were used to measure fasting glucose and total cho-
646
Int Heart J November 2015
CHOU, ET AL
lesterol. Three well-trained technicians were assigned to measure blood pressure using the AHA guideline 37) with a noninvasive electronic device, the Omron HEM-7230. Coffee, tea, and tobacco use were forbidden for 30 minutes before a measurement. Each patient was seated with his or her back supported and hands placed on a desk for support. The cuff bladder was fastened on the upper arm at the level of the heart and both feet were flat on the floor for at least 5 minutes in a quiet room. At least two measurements of blood pressure were taken each time, separated by at least 1 minute. The average of the two measurements was used as the study variable. Statistical analysis: All variables were recorded as the mean ± standard deviation or percentage. The χ2 test and one-way ANOVA were used to test the differences in characteristics between male and female participants. The Spearman correlation coefficients were determined to explore the associations between selected covariates and baPWV. Multiple linear regression analysis was used to identify the job-related factors significantly associated with arteriosclerosis. Model 1 included only job-related factors in the model. Model 2 further included age, gender, education, and medical profession in the model. Model 3 further adjusted for smoking, BMI, heart rate, systolic blood pressure, diastolic blood pressure, fasting sugar, as well as total cholesterol in addition to the variables adjusted in Model 2. All statistical analyses were performed using SPSS version 17 software, with the level of significance set at P < 0.05.
Results Characteristics of participants: The socio-demographic fac-
tors, job-related psychosocial factors, cardiovascular risk factors, mental health, and pulse wave velocity of the participants by totals and gender are summarized in Table I. The participants were predominantly female (85.2%). The mean age of all the subjects was 40.5 years and males were 4 years older than females. Most nurse professionals were female and physicians were male. There were no significant gender differences with respect to education, sleep duration per day, proportion of extra work hours and shift work, severity of mental health, and values of fasting glucose and cholesterol. Females had significantly lower social support (45.8% versus 25.9%, P < 0.001). At the same time, females had a significantly lower frequency of current smoking, lower body mass index, and systolic and diastolic blood pressure than males. Moreover, the value of baPWV was lower in females (P < 0.001). Factors associated with arteriosclerosis (baPWV): Table II shows the correlation coefficients between study factors and baPWV. The results demonstrate that baPWV was strongly associated with gender, age, profession, work hours, work type, and all the traditional cardiovascular risk factors except smoking. There was a weak association between baPWV and mental health. Unexpectedly, we noted that baPWV was not significantly associated with job demand, job control, social support, and heart rate. Work-related hazards and arteriosclerosis (baPWV): The associations between work-related factors and arteriosclerosis are shown in Table III. When all the work-related hazards were examined simultaneously, the results showed that the study participants whose daily sleep duration was less than 6 hours had a significantly higher baPWV, as compared to those who
slept 6-8 hours. Furthermore, those with work hours less than 40 hours per week were also significantly associated with a higher baPWV compared to 41-49 hours of work per week. There was a U-shaped relationship of baPWV with both sleep duration and work hours per week (Model 1). In Model 2, after adjusting for age, gender, education, and profession, only those who had a sleep duration of less than 6 hours every day showed a significantly higher baPWV. In the full model (Model 3), that was also adjusted for cardiovascular risk factors, the results revealed that participants who had a sleep duration of less than 6 hours per day experienced only a marginal, but significant effect as compared to those who slept 6-8 hours (β = 0.3, 95% CI 0.0-0.6, P = 0.025). Those with a weekly work time of more than 60 hours were also at an increased risk of arteriosclerosis as compared with those who work 41-49 hours per week (β = 0.8, 95% CI 0.2-1.5, P = 0.012). Surprisingly, shift work, job control, job demands, social support, and depression all showed no significant association with baPWV in the regression models. The full model can explain about half of the variance of baPWV (r2= 0.491; adjusted r2= 0.466).
Discussion This is the first study to explore the relationship between work-related conditions and arteriosclerosis in Taiwanese medical employees. The main findings showed that after adjusting for all co-variables, only short sleep duration (< 6 hours/day) and long work hours (> 60 hours/week) were associated with a higher risk of arteriosclerosis evaluated by baPWV. These associations had non-linear (U-shaped) relationships and with only marginal effect. Other work-related hazards (including high job demand, low job control, low social support, doing shift work or night work, and depression) had no correlation to arteriosclerosis. Only two studies using Japanese subjects have addressed the same relationship between work-related hazards and arteriosclerosis as this study. The first was a cross-sectional study conducted on 396 young Japanese male workers. After full adjustment of cardiovascular risk factors and control of psychological responses, job strain demonstrated a negative association to baPWV, which is inconsistent with previous results.20) The other study was a large-scale screening conducted on 4,266 subjects (80% male) who worked for local governments. The results showed that high job strain was only associated with high baPWV in women, and high job demand was not related to either of the genders.21) The same results were also seen in the CARDIA study 19) in Americans, which indicated low job control, high job demands, and job strain were not associated with coronary calcium score (a subclinical atherosclerosis). One case-control study that examined the relationship between occupational hazards and acute coronary heart disease in male Taiwanese found that longer work hours (> 60 hours/ week) and shorter sleep duration (< 6 hours/day), but not job demands, job control, and shift work, result in a significant increase in the incidence of acute myocardial infarction (odd ratio 2.7 and 3.3, separately).38) These findings were compatible with the results of the present study. The above evidence raises the possibility that work time and sleep duration may be more suitable occupational variables, especially for Asian and modern societies,
Vol 56 No 6
647
PSYCHOSOCIAL HAZARDS AND ARTERIOSCLEROSIS Table I. Characteristic of Study Participants (n = 576) Variable Age, years Education (%) High school or less College University or above Profession (%) Physician Nurse Medical technician Administrator Sleep duration (hours/day) (%) 8 Work hours (hours/week) (%) ≦ 40 41-49 50-59 ≧ 60 Work type (%) Day work Night work Shift work Job demand (%) Low Median High Job control (%) High Median Low Job support (%) Low High Current/or ex- smoking (%) No Yes Body mass index, kg/m2 Heart rate, beats/minute SBP, mmHg DBP, mmHg Fasting glucose, mg/dL Total cholesterol, mg/dL Mental Health baPWV, m/second
Female (n = 491)
Gender Male (n = 85)
40.1 ± 8.4
39.47 ± 8.1
43.4 ± 9.4
13.9 29.0 57.1
12.8 30.1 57.0
20.0 22.4 57.6
2.8 40.3 15.3 41.7
1.0 46.8 12.6 39.5
12.9 2.4 30.6 54.1
43.1 53.6 3.3
43.0 53.6 3.5
43.5 54.1 2.4
43.2 38.4 13.2 5.2
43.4 38.3 13.2 5.1
42.4 38.3 12.9 5.9
58.2 2.3 39.6
56.2 2.6 41.1
69.4 0.0 30.6
19.3 31.8 49.0
18.5 30.5 50.9
37.6 38.8 23.5
34.4 38.7 26.9
32.6 39.5 27.9
44.7 34.1 21.2
42.9 57.1
45.8 54.2
25.9 74.1
94.1 5.9 22.7 ± 3.6 82.4 ± 14.1 125.9 ± 16.7 79.4 ± 11.3 72.2 ± 46.1 149.9 ± 88.2 12.5 ± 8.7 11.4 ± 2.2
98.2 1.8 22.4 ± 3.5 82.6 ± 13.4 124.2 ± 16.3 78.7 ± 11.3 71.6 ± 46.0 148.5 ± 87.2 12.7 ± 8.9 11.2 ± 2.0
70.6 29.4 24.8 ± 3.5 81.0 ± 18.1 135.5 ± 16.1 83.6 ± 10.2 76.0 ± 46.4 158.4 ± 93.9 11.1 ± 7.7 12.7 ± 2.9
Total
P < 0.001 0.122
< 0.001
0.869
0.990
< 0.040
0.078
0.088
0.001 < 0.001 < 0.001 0.331 < 0.001 < 0.001 0.409 0.337 0.111 < 0.001
SBP indicates systolic blood pressure; DBP, diastolic blood pressure; and baPWV, brachial-ankle pulse wave velocity.
than traditional stress models of work load and decisional latitude to evaluate the early vascular damage of atherosclerosis. However, this inference and its possible biological mechanism need more research for clarification. Long work hours are associated with stress, dissatisfaction, an unhealthy lifestyle, and adverse health outcomes such as hypertension, sleep disorders, musculoskeletal problems, psychological problems, and unhealthy lifestyles.8,39,40) Moreover, overtime work increases the risk of cardiovascular disease. Vertinan, et al conducted a meta-analysis that included 12 trials with a total of 22,518 participants. They concluded that the relative risk of coronary heart disease for long work hours is between 1.80 and 1.59 (minimally to maximally adjusted analysis). Furthermore, the results of longitudinal follow-up studies
show employees with long work hours possess about a 40% increased risk of developing coronary heart disease.41) This study showed overtime work is associated with a higher risk of arteriosclerosis. Indeed, overtime work is very common in East Asian countries, including Taiwan. The Japanese word “Karoshi,” which means death from overwork, was first reported in Japan in 1969.42) Over the subsequent decades, the Japanese government has taken the initiative to bring down the number of work hours to improve the health of employees and their quality of life. Japanese people worked an average of 1,745.2 hours a year in 2012. At the same time, the annual working time of employees in Taiwan was 2,140.8 hours, which is much longer than those in Western countries such as the United States, Canada, England, and Germany, whose em-
648
Int Heart J November 2015
CHOU, ET AL
ployees worked between 1396.6 and 1789.9 hours.43,44) Thus, in Taiwan and other East Asian countries such as Singapore and Hong Kong, the issue of overtime being a threat to the Table II. Correlation Coefficients Between baPWV and Covariates (n = 576) Variable
Correlation coefficients
Gender Age, years Education Profession Sleep duration (hours/day) Work hours (hours/week) Work type Job control Job demand Job support Mental health Smoking status Body mass index, kg/m2 Heart rate, beats/minute SBP, mmHg DBP, mmHg Fasting glucose, mg/dL Total cholesterol, mg/dL
0.249 0.543 -0.035 0.251 0.047 -0.134 -0.133 -0.006 -0.063 -0.050 -0.082 0.038 0.266 0.006 0.564 0.487 0.345 0.169
P < 0.001 < 0.001 0.404 < 0.001 0.264 0.001 0.001 0.877 0.133 0.231 0.049 0.367 < 0.001 0.881 < 0.001 < 0.001 < 0.001 < 0.001
SBP indicates systolic blood pressure; DBP, diastolic blood pressure; and baPWV, brachial-ankle pulse wave velocity.
workers’ health can never be overemphasized and is not yet resolved. Sleep duration is another risk for CVD. Previous studies elucidate that both short and long sleep durations are associated with increases in the incidence of and mortality from cardiovascular disease.12,13) A large Japanese prospective cohort study that included 12) a total of 98,634 participants with a mean follow-up of 14.3 years demonstrated that, as compared with 7 hours of sleep, sleep durations of 4 hours or less are associated with increased mortality from coronary artery disease, as well as all causes of mortality in both genders. The hazard ratios were 2.32 (95% CI, 1.19-4.50) for coronary artery disease in women, and were 1.29 (1.02-1.64) and 1.28 (1.03-1.60) for all causes of mortality in men and women, respectively. On the other hand, sleep durations of 10 hours or longer were associated with 1.5- to 2-fold increases in mortality from total and ischemic stroke, total cardiovascular disease, and all causes for women and men, compared with 7 hours of sleep. Previous research from the Whitehall II cohort study and Japanese cohort studies all yielded a U-shaped relationship between sleep duration and mortality from cardiovascular disease, with the lowest one at 7 hours of sleep.12,45,46) The present findings also showed that sleep times of less than 6 hours or longer than 8 hours tended to increase the risk of arteriosclerosis when compared with sleep of 6-8 hours, although the difference was not statistically significant for sleep times greater than 8 hours.
Table III. Multiple Linear Regression Analysis of Job Related Factors in Association With baPWV (n = 576) ba-PWV Sleep duration (hours/day) 8 Work hours (hours/week) ≦ 40 41-49 50-59 ≧ 60 Work type Day work Night work Shift work Control High Median Low Demand Low Median High Job support High Low Depression No Yes r2 Adjusted r2
Model 1 β (95%CI)
Model 2 β (95%CI)
Model 3 β (95%CI)
0.7 (0.3~1.1)*** 0 0.1 (-1.1~0.9)
0.4 (0.1~0.8)* 0 0.3 (-0.6~1.2)
0.3 (0.0~0.6)* 0 0.5 (-0.3~1.2)
0.4 (0.1~0.9)* 0 -0.2 (-0.8~0.4) 0.7 (-0.2~1.5)
0.3 (-0.1~0.7) 0 -0.1 (-0.6~0.5) 0.5 (-0.2~1.3)
0.1 (-0.2~0.4) 0 -0.0 (-0.5~0.4) 0.8 (0.2~1.5)*
0 -0.5 (-1.7~0.7) -0.3 (-0.7~0.1)
0 0.3 (-0.8~1.4) 0.2 (-0.2~0.5)
0 -0.0 (-0.9~0.9) 0.1 (-0.2~0.4)
0 0.2 (-0.3~0.6) 0.1 (-0.4~0.6)
0 0.2 (-0.2~0.6) 0.2 (-0.3~0.6)
0 0.2 (-0.2~0.5) 0.2 (-0.2~0.6)
0 0.1 (-0.4~0.6) -0.2 (-0.7~0.4)
0 -0.0 (-0.5~0.4) -0.0 (-0.5~0.4)
0 -0.1 (0.5~0.3) -0.2 (-0.5~0.2)
0 -0.1 (-0.4~0.3)
0 -0.0 (-0.4~0.3)
0 -0.0 (-0.3~0.3)
0 -0.1 (-0.5~0.2) 0.052 0.030
0 -0.2 (-0.6~0.3) 0.272 0.245
0 -0.1 (-0.5~0.2) 0.491 0.0466
* P < 0.05, ***P < 0.001. Model 1: only include the selected job-related factors in the model without further adjustment for other variables, Model 2: further adjusted by age, gender, education, profession, Model 3: adjusted by variables in model 2 as well as smoking status, body mass index, heart rate, systolic blood pressure, diastolic blood pressure, fasting glucose, and total cholesterol.
Vol 56 No 6
PSYCHOSOCIAL HAZARDS AND ARTERIOSCLEROSIS
Using baPWV to assess arteriosclerosis with an autonomic machine is considered a simple and reliable method. Yamashina, et al reported that baPWV was not only closely correlated to the invasive method of aortic PWV (r = 0.87), but also has high reproducibility with Pearson’s correlation coefficient of inter-observer (r = 0.97) and intra-observer (r = 0.87) variability.24) In our study, the value of baPWV had a strong association with age, gender, body mass index, systolic and diastolic blood pressures, fasting glucose, and cholesterol. These results were consistent with previous reports 25-28) and support the evidence that baPWV is a reliable predictor of arteriosclerosis, even in Taiwanese subjects. To the best of our knowledge, this study is the first report to explore the relationship of work-related psychosocial hazards and arteriosclerosis evaluated by baPWV in Taiwan. Furthermore, this may be the first report on the linkage of job stress and pre-clinical cardiovascular disease in medical employees in the world. We have comprehensively adjusted all the traditional cardiovascular risk factors and mental health parameters to avoid possible confounders. This adjustment can improve the validity of the results. In addition, we also examined most of the work-related hazards including job demands, job control, social support, shift work, mental health, sleep duration, and work hours at the same time in our analysis. Several limitations should be addressed in this research. First, although the measurement of baPWV is a simple technique with good reliability and reproducibility, its calculation of path length comes from a height-based formula rather than actually measuring the brachial to ankle distance. Also, this formula is derived from the anthropometric data of the Japanese population. Thus, systemic errors due to the baPWV tool may be produced. However, the height of Taiwanese is similar to that of Japanese. This characteristic can mitigate the level of error found when Western countries use baPWV. Second, the subjects of this study were sampled from medical employees; the results should not be extrapolated to other occupational workers. Third, although the sample size was modest and females were predominant (85.2%), we only showed the results that amalgamate both genders. However, our final results (Table III) were adjusted for the gender factor to decrease this effect. Finally, the inherent shortcoming of a cross-sectional survey may weaken the causal relationship between work-related hazards and arteriosclerosis. Therefore, further longitudinal study is needed to confirm these relationships. Conclusion: This study demonstrates that only short sleep duration and long work hours increase the risk of arteriosclerosis measured by baPWV. Other occupational hazards including high work load, low job control, low social support, doing shift work, and depression were not correlated to early atherosclerosis. These findings should make it easier for the employer or government to stipulate rational work hours in order to avoid the development of cardiovascular disease among their employees. Further longitudinal studies are warranted to elucidate the relationship between work-related hazards and arteriosclerosis.
Disclosure All authors have no relationships that present potential conflict of interest to report and none have received any finan-
649
cial support.
References
1. Lloyd-Jones DM, Hong Y, Labarthe D, et al. Defining and setting national goals for cardiovascular health promotion and disease reduction: the American Heart Association’s Strategic Impact Goal through 2020 and beyond. Circulation 2010; 121: 586-613. (Review) 2. Go AS, Mozaffarian D, Roger VL, et al. Heart disease and stroke statistics--2013 update: a report from the American Heart Association. Circulation 2013; 127: e6-e245. (Review) 3. Ford ES, Ajani UA, Croft JB, et al. Explaining the decrease in U.S. deaths from coronary disease, 1980–2000. N Engl J Med 2007; 356: 2388-98. 4. Yusuf S, Hawken S, Ounpuu S, et al. Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case-control study. Lancet 2004; 364: 937-52. 5. Karasek RA Jr. Job demands, job decision latitude, and mental strain: Implications for job redesign. Adm Sci Q 1979; 24: 285308. 6. Kivimäki M, Nyberg ST, Batty GD, et al. Job strain as a risk factor for coronary heart disease: a collaborative meta-analysis of individual participant data. Lancet 2012; 380: 1491-7. 7. Kang MY, Park H, Seo JC, et al. Long working hours and cardiovascular disease: a meta-analysis of epidemiologic studies. J Occup Environ Med 2012; 54: 532-7. 8. Kang MY, Cho SH, Yoo MS, Kim T, Hong YC. Long working hours may increase risk of coronary heart disease. Am J Ind Med 2014; 57: 1227-34. 9. Jeong I, Rhie J, Kim I, et al. Working hours and cardiovascular disease in Korean workers: a case-control study. J Occup Health 2014; 55: 385-91. 10. Knutsson A, Hallquist J, Reuterwall C, Theorell T, Akerstedt T. Shiftwork and myocardial infarction: a case-control study. Occup Environ Med 1999; 56: 46-50. 11. Charles LE, Fekedulegn D, Burchfiel CM, et al. Associations of work hours with carotid intima-media thickness and ankle-brachial index: the Multi-Ethnic Study of Atherosclerosis (MESA). Occup Environ Med 2012; 69: 713-20. 12. Ikehara S, Iso H, Date C, et al. Association of sleep duration with mortality from cardiovascular disease and other causes for Japanese men and women: the JACC study. Sleep 2009; 32: 295-301. 13. Sabanayagam C, Shankar A. Sleep duration and cardiovascular disease: results from the National Health Interview Survey. Sleep 2010; 33: 1037-42. 14. Dietz LJ, Matthews KA. Depressive symptoms and subclinical markers of cardiovascular disease in adolescents. J Adolesc Health 2011; 48: 579-84. 15. Backé EM, Seidler A, Latza U, Rossnagel K, Schumann B. The role of psychosocial stress at work for the development of cardiovascular diseases: a systematic review. Int Arch Occup Environ Health 2012; 85: 67-79. (Review) 16. Stary HC, Chandler AB, Dinsmore RE, et al. A definition of advanced types of atherosclerotic lesions and a histological classification of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association. Circulation 1995; 92: 1355-74. (Review) 17. Fujishiro K, Diez Roux AV, Landsbergis P, et al. Associations of occupation, job control and job demands with intima-media thickness: the Multi-Ethnic Study of Atherosclerosis (MESA). Occup Environ Med 2011; 68: 319-26. 18. Rosvall M, Ostergren PO, Hedblad B, Isacsson SO, Janzon L, Berglund G. Work-related psychosocial factors and carotid atherosclerosis. Int J Epidemiol 2002; 31: 1169-78. 19. Greenlund KJ, Kiefe CI, Giles WH, Liu K. Associations of job strain and occupation with subclinical atherosclerosis: The CAR-
650
CHOU, ET AL
DIA Study. Ann Epidemiol 2010; 20: 323-31. 20. Nomura K, Nakao M, Karita K, Nishikitani M, Yano E. Association between work-related psychological stress and arterial stiffness measured by brachial-ankle pulse-wave velocity in young Japanese males from an information service company. Scand J Work Environ Health 2005; 31: 352-9. 21. Utsugi M, Saijo Y, Yoshioka E, et al. Relationship between two alternative occupational stress models and arterial stiffness: a crosssectional study among Japanese workers. Int Arch Occup Environ Health 2009; 82: 175-83. 22. Blacher J, Guerin AP, Pannier B, Marchais SJ, Safar ME, London GM. Impact of aortic stiffness on survival in end-stage renal disease. Circulation 1999; 99: 2434-9. 23. Mitchell GF, Hwang SJ, Vasan RS, et al. Arterial stiffness and cardiovascular events: the Framingham Heart Study. Circulation 2010; 121: 505-11. 24. Yamashina A, Tomiyama H, Takeda K, et al. Validity, reproducibility, and clinical significance of noninvasive brachial-ankle pulse wave velocity measurement. Hypertens Res 2002; 25: 359-64. 25. Tomiyama H, Yamashina A, Arai T, et al. Influences of age and gender on results of noninvasive brachial–ankle pulse wave velocity measurement-- a survey of 12517 subjects. Atherosclerosis 2003; 166: 303-9. 26. Fujiwara Y, Chaves P, Takahashi R, et al. Relationships between brachial-ankle pulse wave velocity and conventional atherosclerotic risk factors in community-dwelling people. Prev Med 2004; 39: 1135-42. 27. Hung CS, Lin JW, Hsu CN, et al. Using brachial-ankle pulse wave velocity to associate arterial stiffness with cardiovascular risks. Nutr Metab Cardiovasc Dis 2009; 19: 241-6. 28. Choi KM, Lee KW, Seo JA, et al. Relationship between brachialankle pulse wave velocity and cardiovascular risk factors of the metabolic syndrome. Diabetes Res Clin Pract 2004; 66: 57-61. 29. Imanishi R, Seto S, Toda G, et al. High brachial-ankle pulse wave velocity is an independent predictor of the presence of coronary artery disease in men. Hypertens Res 2004; 27: 71-8. 30. Vlachopoulos C, Aznaouridis K, Terentes-Printzios D, Ioakeimidis N, Stefanadis C. Prediction of cardiovascular events and all-cause mortality with brachial-ankle elasticity index: a systematic review and meta-analysis. Hypertension 2012; 60: 556-62. (Review) 31. Kitahara T, Ono K, Tsuchida A, et al. Impact of brachial-ankle pulse wave velocity and ankle-brachial blood pressure index on mortality in hemodialysis patients. Am J Kidney Dis 2005; 46: 688-96. 32. Yeh WY, Cheng Y, Chen CJ, Hu PY, Kristensen TS. Psychometric properties of the Chinese version of Copenhagen burnout inventory among employees in two companies in Taiwan. Int J Behav Med 2007; 14: 126-33.
Int Heart J November 2015
33. Yeh WY, Cheng YW, Chen MJ, Chiu AW. Development and validation of an occupational burnout inventory. Taiwan J Public Health 2008; 27: 349-64. 34. Chou LP, Li CY, Hu SC. Job stress and burnout in hospital employees: comparisons of different medical professions in a regional hospital in Taiwan. BMJ Open 2014; 4: e004185. 35. Lee Y, Yang MJ, Lai TJ, Chiu NM, Chau TT. Development of the Taiwanese Depression Questionnaire. Chang Gung Med J 2000; 23: 688-94. 36. Lee Y, Lin PY, Hsu ST, Cing-Chi Y, Yang LC, Wen JK. Comparing the use of the Taiwanese Depression Questionnaire and Beck Depression Inventory for screening depression in patients with chronic pain. Chang Gung Med J 2008; 31: 369-77. 37. Pickering TG, Hall JE, Appel LJ, et al. Recommendations for blood pressure measurement in humans: an AHA scientific statement from the Council on High Blood Pressure Research Professional and Public Education Subcommittee. J Clin Hypertens 2005; 7: 102-9. 38. Cheng Y, Du CL, Hwang JJ, Chen IS, Chen MF, Su TC. Working hours, sleep duration and the risk of acute coronary heart disease: a case-control study of middle-aged men in Taiwan. Int J Cardiol 2014; 171: 419-22. 39. Sparks K, Cooper C, Fried Y, Shirom A. The effects of hours of work on health: a meta-analytic review. J Occup Organ Psychol 1997; 70: 391-408. 40. Overtime and Extended Work Shifts: Recent Findings on Illnesses, Injuries and Health Behaviors. DHHS (NIOSH) 2004-143. Available at: http://www.cdc.gov/niosh/docs/2004-143/pdfs/2004-143. pdf. Accessed August 18, 2015. 41. Virtanen M, Heikkilä K, Jokela M, et al. Long working hours and coronary heart disease: a systematic review and meta-analysis. Am J Epidemiol 2012; 176: 586-96. (Review) 42. Nishiyama K, Johnson JV. Karoshi--death from overwork: occupational health consequences of Japanese production management. Int J Health Serv 1997; 27: 625-41. (Review) 43. Average Annual Hours Actually Worked Per Person in Employment. Available at: http://statdb.mol.gov.tw/html/nat/Table%206-1. pdf. Accessed August 18, 2015. 44. OECD. Average annual hours actually worked per worker. Available at: http://stats.oecd.org/ index.aspx?DataSetCode=ANHRS. Accessed August 18, 2015. 45. Ferrie JE, Shipley MJ, Cappuccio FP, et al. A prospective study of change in sleep duration: associations with mortality in the Whitehall II cohort. Sleep 2007; 30: 1659-66. 46. Tamakoshi A, Ohno Y. Self-reported sleep duration as a predictor of all-cause mortality: results from the JACC study, Japan. Sleep 2004; 27: 51-4.
Work-Related Psychosocial Hazards and Arteriosclerosis A Cross-Sectional Study Among Medical Employees in a Regional Hospital in Taiwan Li-Ping Chou,1,2 MD, Chung-Yi Li,2,3 PhD, and Susan C. Hu,2 PhD Summary The association of psychosocial stress with cardiovascular disease (CVD) is still inconclusive. The aim of this study was to examine the relationships between arteriosclerosis and various work-related conditions among medical employees with various job titles. A total of 576 medical employees of a regional hospital in Taiwan with a mean age of 43 years and female gender dominance (85%) were enrolled. Arteriosclerosis was evaluated by brachial-ankle pulse wave velocity (baPWV). Workrelated conditions included job demands, job control, social support, shift work, work hours, sleep duration, and mental health. The crude relationship between each of the selected covariates and baPWV was indicated by Spearman correlation coefficients. A multiple linear regression model was further employed to estimate the adjusted associations of selected covariates with arteriosclerosis. The mean baPWV of participants was 11.4 ± 2.2 m/s, with the value for males being significantly higher than that for females. The baPWV was associated with gender, age, medical profession, work hours, work type, depression, body mass index, systolic and diastolic blood pressures, fasting glucose, and cholesterol. After being fully adjusted by these factors, only sleep duration of less than 6 hours and weekly work hours longer than 60 hours were significantly associated with increased risk of arteriosclerosis. The conditions of job demands, job control, social support, shift work, and depression showed no significant association with baPWV. Longer work hours and shorter sleep durations were associated with an increased risk of arteriosclerosis. These findings should make it easier for the employer or government to stipulate rational work hours in order to avoid the development of cardiovascular disease among their employees. (Int Heart J 2015; 56: 644-650) Key words: Pulse wave velocity, Cardiovascular disease, Stress
C
ardiovascular disease (CVD) is the leading cause of death in most industrialized nations. Multiple risk factors predispose people to the progression of CVD. By controlling these risk factors, the incidence and mortality rate of CVD has been reduced in several industrialized countries in recent decades.1-3) Among these risk factors, psychosocial stress is noted as a widespread phenomenon and plague of modern society. One large-scale and world-wide case control study revealed psychosocial stress was correlated to a 2.67-fold increased risk of acute myocardial infarction, which is a more dangerous condition than that of hypertension and diabetes.4) Many work-related psychosocial stressors are associated with CVD. Karosak, et al commenced pioneering work and developed the dominant demand-control model (DCM) approximately 3 decades ago to study work-related stress.5) Work characteristics of low decision latitude and high work load will result in high job strain. Job strain will increase the risk of incident coronary heart dis-
ease by 23% compared to no job strain in large pooled data.6) Recently, long work hours, 7-10) shift work, 11) short sleep hours,12,13) and depression 14) were also considered to be emerging work-related hazards leading to CVD. Despite the enormous number of papers that have explored the association between job stress and CVD over the last 3 decades, the results are heterogeneous.6,15) Most of these studies come from observational data and nearly half of the results are negative or even in inverse relation between job stress and CVD. There are several inherent methodological limitations in these studies. One of the most important reasons is that the causality between the exposure of stress and the outcome of CVD is a long process and difficult to confirm because atherosclerosis is a pivotal pathological mechanism of CVD and it always progresses very slowly.16) Thus, recently research efforts have focused on the subclinical change of CVD including carotid intima-media thickness,17,18) coronary calcium score,19) and arterial stiffness 20,21) as the study surrogate end-
From the 1 Division of Cardiology, Department of Medicine, Sin-Lau Hospital, 2 Department of Public Health, College of Medicine, National Cheng Kung University, Tainan, and 3 Department of Public Health, College of Public Health, China Medical University, Taichung, Taiwan. Address for correspondence: Susan C. Hu, PhD, Department of Public Health, College of Medicine, National Cheng Kung University, No. 1, University Road, Tainan 70101, Taiwan. E-mail: [email protected] Received for publication April 4, 2015. Revised and accepted May 1, 2015. Released in advance online on J-STAGE November 9, 2015. All rights reserved by the International Heart Journal Association. 644
Vol 56 No 6
PSYCHOSOCIAL HAZARDS AND ARTERIOSCLEROSIS
point. Arteriosclerosis reflects the fibrotic change and poor compliance of arterial vessels, which represents vascular damage and becomes an independent risk factor of CVD.22) There are several methods to measure arterial stiffness, among which pulse wave velocity (PWV) is a simple and noninvasive measurement that has become a popular screening method in recent years.23) Brachial-ankle PWV (baPWV) is a newly developed method which is less time-consuming and less skill-dependant.24) The baPWV method is associated with age, gender, risk factors of CVD, and Framingham risk score, and has been shown to be a good independent predictor of coronary artery disease.25-29) One recent meta-analysis, which collected 18 prospective cohort studies with a total of 8,169 participants and a mean follow-up of 3.6 years, revealed baPWV can predict total cardiovascular events, cardiovascular mortality, and all-cause mortality. The pooled relative risks were 2.95 (95% CI, 1.635.33), 5.36 (95% CI, 2.17-13.27), and 2.45 (95% CI, 1.563.86), respectively.30) The value of baPWV indicates the severity of arteriosclerosis, which is considered to be an early marker of atherosclerosis and is related to later cardiovascular disease. It is anticipated that measuring baPWV and adjusting the potential risk factors of CVD may enable us to clarify the mechanism of occupational hazards and CVD. Only two studies have explored the association between psychosocial stress and arteriosclerosis evaluated by baPWV. Both of these studies came from Japanese subjects.20,21) In addition, these papers only used Karasek’s demand control model and/or Siegrist’s effort reward imbalance model as their independent factors. However, many other work-related hazards including long work hours, shift work, short sleep duration, and psychological problems may also relate to CVD, but have never been studied. To the best of our knowledge, there has never been such a report in Taiwanese employees, especially those who work in hospitals. The aim of this study was to examine the relationship between multiple work-related hazards and arteriosclerosis among medical employees in Taiwan.
Methods Participants and study design: A cross-sectional study design was used. The volunteer participants were recruited from a regional hospital in Tainan, Taiwan. The hospital had 1,490 hospital employees including 150 physicians, 600 nurses, and 740 other medical employees. In May 2013, the hospital administrators conducted a social epidemiologic survey to explore the job-related stressors and health conditions among the employees before the implementation of health-promotion programs. There were 1,329 medical employees who completed the electronic questionnaire (response rate of 89%). Among them, 676 volunteers were measured for arteriosclerosis. We then defined that the valid blood sampling period for glucose and cholesterol should be within 6 months. Finally, 576 professionals were selected as subjects. This study was approved by the Ethics Review Board of Sin Lau Hospital (SLH-919-104-01). Measurement of arteriosclerosis: Arteriosclerosis was measured by non-invasive methods with an automatic waveform analyzer (VaSera VS-1000, Fukuda Denshi, Japan). The measurement of arterial stiffness was performed between 12:00 and 14:00 pm by experienced technicians. The participant laid on a
645
bed for at least 5 minutes, and then the cuffs were wrapped on both sides of their brachia and ankles together. To obtain baPWV, pulse volume wave forms of the brachial and tibia arteries were recorded simultaneously. Path lengths from the heart to the ankle and from the heart to the brachium were marked as La and Lb. La-Lb represents the distance between brachium to ankle and was calculated using the following formula: La-Lb = 0.59 x body height (cm) + 14.4 (modified from Kitahara, et al).31) The time interval between the brachium and ankle is expressed as ΔTab. The baPWV was then calculated as follows: baPWV = (La-Lb)/ΔTab. The higher the value of baPWV, the greater the severity of the arteriosclerosis. In this study, we selected the higher of the right- or left-sided baPWV for our analyses. Socio-demographics, work characteristics: The self-administered questionnaire used included socio-demographic information and work characteristics. Socio-demographic information consisted of gender, age, educational level, marital status, and medical profession. Work characteristics included work hours, work type, and sleep hours. Work hours were calculated as average work hours per week in the previous month, and were classified as ≦ 40 hours, 41-49 hours, 50-59 hours, and ≧ 60 hours. Work type included fixed day work, fixed night work, and shift work. Sleep hours were categorized as < 6 hours, 6-8 hours, and > 8 hours in everyday sleep. Measurement of job stress: A Chinese version of the Job Content Questionnaire (C-JCQ) was chosen to measure job strain. C-JCQ is derived from the Karasek Demand-Control-Support model and has been validated and used with success in Taiwanese subjects.32,33) Job demands, mean work load, and job control represent decision latitude. As in Karasek’s model, work that possesses the characteristics of high job demand and low job control resulted in high job strain, which, in turn, creates the highest risk of CVD. Social support was an effect modifier and was later added in the domain of the demand control model. Therefore, C-JCQ consisted of 3 subscales: 9 questions on job demands, 8 questions on job control, and 8 questions on social support. Each question was measured on a 4-point scale. The scores of job demands and control were calculated separately and divided into tertiles to indicate high, medium, and low in this study. The scores of social support were expressed as high (score ≧ 24) and low (score < 24). Detailed descriptions of the C-JCQ can be found in a previously published paper.34) Measurement of mental health: Because the way of emotional expressions varies with culture, we used the “Taiwanese Depression Questionnaire” (TDQ) to screen the prevalence of depression in our study participants. The 18-item TDQ had a sensitivity and specificity of 0.89 and 0.92, respectively, at the cutoff score of 19. It was superior to the Beck Depression Inventory in detecting depressive patients in Taiwan.35,36) Thus, for this study we selected a cut-off point score of ≧ 19 to indicate the presence of depression. Cardiovascular risk factor survey: Cardiovascular risk factors included smoking status, body mass index (BMI), fasting glucose, total cholesterol, and hypertension, all of which were obtained from the employees’ health profiles. Smoking status was classified as “current/or ex-smoker” or “never.” The BMI was measured as body weight in kilograms divided by the square of body height in meters (kg/m2). Standard laboratory techniques were used to measure fasting glucose and total cho-
646
Int Heart J November 2015
CHOU, ET AL
lesterol. Three well-trained technicians were assigned to measure blood pressure using the AHA guideline 37) with a noninvasive electronic device, the Omron HEM-7230. Coffee, tea, and tobacco use were forbidden for 30 minutes before a measurement. Each patient was seated with his or her back supported and hands placed on a desk for support. The cuff bladder was fastened on the upper arm at the level of the heart and both feet were flat on the floor for at least 5 minutes in a quiet room. At least two measurements of blood pressure were taken each time, separated by at least 1 minute. The average of the two measurements was used as the study variable. Statistical analysis: All variables were recorded as the mean ± standard deviation or percentage. The χ2 test and one-way ANOVA were used to test the differences in characteristics between male and female participants. The Spearman correlation coefficients were determined to explore the associations between selected covariates and baPWV. Multiple linear regression analysis was used to identify the job-related factors significantly associated with arteriosclerosis. Model 1 included only job-related factors in the model. Model 2 further included age, gender, education, and medical profession in the model. Model 3 further adjusted for smoking, BMI, heart rate, systolic blood pressure, diastolic blood pressure, fasting sugar, as well as total cholesterol in addition to the variables adjusted in Model 2. All statistical analyses were performed using SPSS version 17 software, with the level of significance set at P < 0.05.
Results Characteristics of participants: The socio-demographic fac-
tors, job-related psychosocial factors, cardiovascular risk factors, mental health, and pulse wave velocity of the participants by totals and gender are summarized in Table I. The participants were predominantly female (85.2%). The mean age of all the subjects was 40.5 years and males were 4 years older than females. Most nurse professionals were female and physicians were male. There were no significant gender differences with respect to education, sleep duration per day, proportion of extra work hours and shift work, severity of mental health, and values of fasting glucose and cholesterol. Females had significantly lower social support (45.8% versus 25.9%, P < 0.001). At the same time, females had a significantly lower frequency of current smoking, lower body mass index, and systolic and diastolic blood pressure than males. Moreover, the value of baPWV was lower in females (P < 0.001). Factors associated with arteriosclerosis (baPWV): Table II shows the correlation coefficients between study factors and baPWV. The results demonstrate that baPWV was strongly associated with gender, age, profession, work hours, work type, and all the traditional cardiovascular risk factors except smoking. There was a weak association between baPWV and mental health. Unexpectedly, we noted that baPWV was not significantly associated with job demand, job control, social support, and heart rate. Work-related hazards and arteriosclerosis (baPWV): The associations between work-related factors and arteriosclerosis are shown in Table III. When all the work-related hazards were examined simultaneously, the results showed that the study participants whose daily sleep duration was less than 6 hours had a significantly higher baPWV, as compared to those who
slept 6-8 hours. Furthermore, those with work hours less than 40 hours per week were also significantly associated with a higher baPWV compared to 41-49 hours of work per week. There was a U-shaped relationship of baPWV with both sleep duration and work hours per week (Model 1). In Model 2, after adjusting for age, gender, education, and profession, only those who had a sleep duration of less than 6 hours every day showed a significantly higher baPWV. In the full model (Model 3), that was also adjusted for cardiovascular risk factors, the results revealed that participants who had a sleep duration of less than 6 hours per day experienced only a marginal, but significant effect as compared to those who slept 6-8 hours (β = 0.3, 95% CI 0.0-0.6, P = 0.025). Those with a weekly work time of more than 60 hours were also at an increased risk of arteriosclerosis as compared with those who work 41-49 hours per week (β = 0.8, 95% CI 0.2-1.5, P = 0.012). Surprisingly, shift work, job control, job demands, social support, and depression all showed no significant association with baPWV in the regression models. The full model can explain about half of the variance of baPWV (r2= 0.491; adjusted r2= 0.466).
Discussion This is the first study to explore the relationship between work-related conditions and arteriosclerosis in Taiwanese medical employees. The main findings showed that after adjusting for all co-variables, only short sleep duration (< 6 hours/day) and long work hours (> 60 hours/week) were associated with a higher risk of arteriosclerosis evaluated by baPWV. These associations had non-linear (U-shaped) relationships and with only marginal effect. Other work-related hazards (including high job demand, low job control, low social support, doing shift work or night work, and depression) had no correlation to arteriosclerosis. Only two studies using Japanese subjects have addressed the same relationship between work-related hazards and arteriosclerosis as this study. The first was a cross-sectional study conducted on 396 young Japanese male workers. After full adjustment of cardiovascular risk factors and control of psychological responses, job strain demonstrated a negative association to baPWV, which is inconsistent with previous results.20) The other study was a large-scale screening conducted on 4,266 subjects (80% male) who worked for local governments. The results showed that high job strain was only associated with high baPWV in women, and high job demand was not related to either of the genders.21) The same results were also seen in the CARDIA study 19) in Americans, which indicated low job control, high job demands, and job strain were not associated with coronary calcium score (a subclinical atherosclerosis). One case-control study that examined the relationship between occupational hazards and acute coronary heart disease in male Taiwanese found that longer work hours (> 60 hours/ week) and shorter sleep duration (< 6 hours/day), but not job demands, job control, and shift work, result in a significant increase in the incidence of acute myocardial infarction (odd ratio 2.7 and 3.3, separately).38) These findings were compatible with the results of the present study. The above evidence raises the possibility that work time and sleep duration may be more suitable occupational variables, especially for Asian and modern societies,
Vol 56 No 6
647
PSYCHOSOCIAL HAZARDS AND ARTERIOSCLEROSIS Table I. Characteristic of Study Participants (n = 576) Variable Age, years Education (%) High school or less College University or above Profession (%) Physician Nurse Medical technician Administrator Sleep duration (hours/day) (%) 8 Work hours (hours/week) (%) ≦ 40 41-49 50-59 ≧ 60 Work type (%) Day work Night work Shift work Job demand (%) Low Median High Job control (%) High Median Low Job support (%) Low High Current/or ex- smoking (%) No Yes Body mass index, kg/m2 Heart rate, beats/minute SBP, mmHg DBP, mmHg Fasting glucose, mg/dL Total cholesterol, mg/dL Mental Health baPWV, m/second
Female (n = 491)
Gender Male (n = 85)
40.1 ± 8.4
39.47 ± 8.1
43.4 ± 9.4
13.9 29.0 57.1
12.8 30.1 57.0
20.0 22.4 57.6
2.8 40.3 15.3 41.7
1.0 46.8 12.6 39.5
12.9 2.4 30.6 54.1
43.1 53.6 3.3
43.0 53.6 3.5
43.5 54.1 2.4
43.2 38.4 13.2 5.2
43.4 38.3 13.2 5.1
42.4 38.3 12.9 5.9
58.2 2.3 39.6
56.2 2.6 41.1
69.4 0.0 30.6
19.3 31.8 49.0
18.5 30.5 50.9
37.6 38.8 23.5
34.4 38.7 26.9
32.6 39.5 27.9
44.7 34.1 21.2
42.9 57.1
45.8 54.2
25.9 74.1
94.1 5.9 22.7 ± 3.6 82.4 ± 14.1 125.9 ± 16.7 79.4 ± 11.3 72.2 ± 46.1 149.9 ± 88.2 12.5 ± 8.7 11.4 ± 2.2
98.2 1.8 22.4 ± 3.5 82.6 ± 13.4 124.2 ± 16.3 78.7 ± 11.3 71.6 ± 46.0 148.5 ± 87.2 12.7 ± 8.9 11.2 ± 2.0
70.6 29.4 24.8 ± 3.5 81.0 ± 18.1 135.5 ± 16.1 83.6 ± 10.2 76.0 ± 46.4 158.4 ± 93.9 11.1 ± 7.7 12.7 ± 2.9
Total
P < 0.001 0.122
< 0.001
0.869
0.990
< 0.040
0.078
0.088
0.001 < 0.001 < 0.001 0.331 < 0.001 < 0.001 0.409 0.337 0.111 < 0.001
SBP indicates systolic blood pressure; DBP, diastolic blood pressure; and baPWV, brachial-ankle pulse wave velocity.
than traditional stress models of work load and decisional latitude to evaluate the early vascular damage of atherosclerosis. However, this inference and its possible biological mechanism need more research for clarification. Long work hours are associated with stress, dissatisfaction, an unhealthy lifestyle, and adverse health outcomes such as hypertension, sleep disorders, musculoskeletal problems, psychological problems, and unhealthy lifestyles.8,39,40) Moreover, overtime work increases the risk of cardiovascular disease. Vertinan, et al conducted a meta-analysis that included 12 trials with a total of 22,518 participants. They concluded that the relative risk of coronary heart disease for long work hours is between 1.80 and 1.59 (minimally to maximally adjusted analysis). Furthermore, the results of longitudinal follow-up studies
show employees with long work hours possess about a 40% increased risk of developing coronary heart disease.41) This study showed overtime work is associated with a higher risk of arteriosclerosis. Indeed, overtime work is very common in East Asian countries, including Taiwan. The Japanese word “Karoshi,” which means death from overwork, was first reported in Japan in 1969.42) Over the subsequent decades, the Japanese government has taken the initiative to bring down the number of work hours to improve the health of employees and their quality of life. Japanese people worked an average of 1,745.2 hours a year in 2012. At the same time, the annual working time of employees in Taiwan was 2,140.8 hours, which is much longer than those in Western countries such as the United States, Canada, England, and Germany, whose em-
648
Int Heart J November 2015
CHOU, ET AL
ployees worked between 1396.6 and 1789.9 hours.43,44) Thus, in Taiwan and other East Asian countries such as Singapore and Hong Kong, the issue of overtime being a threat to the Table II. Correlation Coefficients Between baPWV and Covariates (n = 576) Variable
Correlation coefficients
Gender Age, years Education Profession Sleep duration (hours/day) Work hours (hours/week) Work type Job control Job demand Job support Mental health Smoking status Body mass index, kg/m2 Heart rate, beats/minute SBP, mmHg DBP, mmHg Fasting glucose, mg/dL Total cholesterol, mg/dL
0.249 0.543 -0.035 0.251 0.047 -0.134 -0.133 -0.006 -0.063 -0.050 -0.082 0.038 0.266 0.006 0.564 0.487 0.345 0.169
P < 0.001 < 0.001 0.404 < 0.001 0.264 0.001 0.001 0.877 0.133 0.231 0.049 0.367 < 0.001 0.881 < 0.001 < 0.001 < 0.001 < 0.001
SBP indicates systolic blood pressure; DBP, diastolic blood pressure; and baPWV, brachial-ankle pulse wave velocity.
workers’ health can never be overemphasized and is not yet resolved. Sleep duration is another risk for CVD. Previous studies elucidate that both short and long sleep durations are associated with increases in the incidence of and mortality from cardiovascular disease.12,13) A large Japanese prospective cohort study that included 12) a total of 98,634 participants with a mean follow-up of 14.3 years demonstrated that, as compared with 7 hours of sleep, sleep durations of 4 hours or less are associated with increased mortality from coronary artery disease, as well as all causes of mortality in both genders. The hazard ratios were 2.32 (95% CI, 1.19-4.50) for coronary artery disease in women, and were 1.29 (1.02-1.64) and 1.28 (1.03-1.60) for all causes of mortality in men and women, respectively. On the other hand, sleep durations of 10 hours or longer were associated with 1.5- to 2-fold increases in mortality from total and ischemic stroke, total cardiovascular disease, and all causes for women and men, compared with 7 hours of sleep. Previous research from the Whitehall II cohort study and Japanese cohort studies all yielded a U-shaped relationship between sleep duration and mortality from cardiovascular disease, with the lowest one at 7 hours of sleep.12,45,46) The present findings also showed that sleep times of less than 6 hours or longer than 8 hours tended to increase the risk of arteriosclerosis when compared with sleep of 6-8 hours, although the difference was not statistically significant for sleep times greater than 8 hours.
Table III. Multiple Linear Regression Analysis of Job Related Factors in Association With baPWV (n = 576) ba-PWV Sleep duration (hours/day) 8 Work hours (hours/week) ≦ 40 41-49 50-59 ≧ 60 Work type Day work Night work Shift work Control High Median Low Demand Low Median High Job support High Low Depression No Yes r2 Adjusted r2
Model 1 β (95%CI)
Model 2 β (95%CI)
Model 3 β (95%CI)
0.7 (0.3~1.1)*** 0 0.1 (-1.1~0.9)
0.4 (0.1~0.8)* 0 0.3 (-0.6~1.2)
0.3 (0.0~0.6)* 0 0.5 (-0.3~1.2)
0.4 (0.1~0.9)* 0 -0.2 (-0.8~0.4) 0.7 (-0.2~1.5)
0.3 (-0.1~0.7) 0 -0.1 (-0.6~0.5) 0.5 (-0.2~1.3)
0.1 (-0.2~0.4) 0 -0.0 (-0.5~0.4) 0.8 (0.2~1.5)*
0 -0.5 (-1.7~0.7) -0.3 (-0.7~0.1)
0 0.3 (-0.8~1.4) 0.2 (-0.2~0.5)
0 -0.0 (-0.9~0.9) 0.1 (-0.2~0.4)
0 0.2 (-0.3~0.6) 0.1 (-0.4~0.6)
0 0.2 (-0.2~0.6) 0.2 (-0.3~0.6)
0 0.2 (-0.2~0.5) 0.2 (-0.2~0.6)
0 0.1 (-0.4~0.6) -0.2 (-0.7~0.4)
0 -0.0 (-0.5~0.4) -0.0 (-0.5~0.4)
0 -0.1 (0.5~0.3) -0.2 (-0.5~0.2)
0 -0.1 (-0.4~0.3)
0 -0.0 (-0.4~0.3)
0 -0.0 (-0.3~0.3)
0 -0.1 (-0.5~0.2) 0.052 0.030
0 -0.2 (-0.6~0.3) 0.272 0.245
0 -0.1 (-0.5~0.2) 0.491 0.0466
* P < 0.05, ***P < 0.001. Model 1: only include the selected job-related factors in the model without further adjustment for other variables, Model 2: further adjusted by age, gender, education, profession, Model 3: adjusted by variables in model 2 as well as smoking status, body mass index, heart rate, systolic blood pressure, diastolic blood pressure, fasting glucose, and total cholesterol.
Vol 56 No 6
PSYCHOSOCIAL HAZARDS AND ARTERIOSCLEROSIS
Using baPWV to assess arteriosclerosis with an autonomic machine is considered a simple and reliable method. Yamashina, et al reported that baPWV was not only closely correlated to the invasive method of aortic PWV (r = 0.87), but also has high reproducibility with Pearson’s correlation coefficient of inter-observer (r = 0.97) and intra-observer (r = 0.87) variability.24) In our study, the value of baPWV had a strong association with age, gender, body mass index, systolic and diastolic blood pressures, fasting glucose, and cholesterol. These results were consistent with previous reports 25-28) and support the evidence that baPWV is a reliable predictor of arteriosclerosis, even in Taiwanese subjects. To the best of our knowledge, this study is the first report to explore the relationship of work-related psychosocial hazards and arteriosclerosis evaluated by baPWV in Taiwan. Furthermore, this may be the first report on the linkage of job stress and pre-clinical cardiovascular disease in medical employees in the world. We have comprehensively adjusted all the traditional cardiovascular risk factors and mental health parameters to avoid possible confounders. This adjustment can improve the validity of the results. In addition, we also examined most of the work-related hazards including job demands, job control, social support, shift work, mental health, sleep duration, and work hours at the same time in our analysis. Several limitations should be addressed in this research. First, although the measurement of baPWV is a simple technique with good reliability and reproducibility, its calculation of path length comes from a height-based formula rather than actually measuring the brachial to ankle distance. Also, this formula is derived from the anthropometric data of the Japanese population. Thus, systemic errors due to the baPWV tool may be produced. However, the height of Taiwanese is similar to that of Japanese. This characteristic can mitigate the level of error found when Western countries use baPWV. Second, the subjects of this study were sampled from medical employees; the results should not be extrapolated to other occupational workers. Third, although the sample size was modest and females were predominant (85.2%), we only showed the results that amalgamate both genders. However, our final results (Table III) were adjusted for the gender factor to decrease this effect. Finally, the inherent shortcoming of a cross-sectional survey may weaken the causal relationship between work-related hazards and arteriosclerosis. Therefore, further longitudinal study is needed to confirm these relationships. Conclusion: This study demonstrates that only short sleep duration and long work hours increase the risk of arteriosclerosis measured by baPWV. Other occupational hazards including high work load, low job control, low social support, doing shift work, and depression were not correlated to early atherosclerosis. These findings should make it easier for the employer or government to stipulate rational work hours in order to avoid the development of cardiovascular disease among their employees. Further longitudinal studies are warranted to elucidate the relationship between work-related hazards and arteriosclerosis.
Disclosure All authors have no relationships that present potential conflict of interest to report and none have received any finan-
649
cial support.
References
1. Lloyd-Jones DM, Hong Y, Labarthe D, et al. Defining and setting national goals for cardiovascular health promotion and disease reduction: the American Heart Association’s Strategic Impact Goal through 2020 and beyond. Circulation 2010; 121: 586-613. (Review) 2. Go AS, Mozaffarian D, Roger VL, et al. Heart disease and stroke statistics--2013 update: a report from the American Heart Association. Circulation 2013; 127: e6-e245. (Review) 3. Ford ES, Ajani UA, Croft JB, et al. Explaining the decrease in U.S. deaths from coronary disease, 1980–2000. N Engl J Med 2007; 356: 2388-98. 4. Yusuf S, Hawken S, Ounpuu S, et al. Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case-control study. Lancet 2004; 364: 937-52. 5. Karasek RA Jr. Job demands, job decision latitude, and mental strain: Implications for job redesign. Adm Sci Q 1979; 24: 285308. 6. Kivimäki M, Nyberg ST, Batty GD, et al. Job strain as a risk factor for coronary heart disease: a collaborative meta-analysis of individual participant data. Lancet 2012; 380: 1491-7. 7. Kang MY, Park H, Seo JC, et al. Long working hours and cardiovascular disease: a meta-analysis of epidemiologic studies. J Occup Environ Med 2012; 54: 532-7. 8. Kang MY, Cho SH, Yoo MS, Kim T, Hong YC. Long working hours may increase risk of coronary heart disease. Am J Ind Med 2014; 57: 1227-34. 9. Jeong I, Rhie J, Kim I, et al. Working hours and cardiovascular disease in Korean workers: a case-control study. J Occup Health 2014; 55: 385-91. 10. Knutsson A, Hallquist J, Reuterwall C, Theorell T, Akerstedt T. Shiftwork and myocardial infarction: a case-control study. Occup Environ Med 1999; 56: 46-50. 11. Charles LE, Fekedulegn D, Burchfiel CM, et al. Associations of work hours with carotid intima-media thickness and ankle-brachial index: the Multi-Ethnic Study of Atherosclerosis (MESA). Occup Environ Med 2012; 69: 713-20. 12. Ikehara S, Iso H, Date C, et al. Association of sleep duration with mortality from cardiovascular disease and other causes for Japanese men and women: the JACC study. Sleep 2009; 32: 295-301. 13. Sabanayagam C, Shankar A. Sleep duration and cardiovascular disease: results from the National Health Interview Survey. Sleep 2010; 33: 1037-42. 14. Dietz LJ, Matthews KA. Depressive symptoms and subclinical markers of cardiovascular disease in adolescents. J Adolesc Health 2011; 48: 579-84. 15. Backé EM, Seidler A, Latza U, Rossnagel K, Schumann B. The role of psychosocial stress at work for the development of cardiovascular diseases: a systematic review. Int Arch Occup Environ Health 2012; 85: 67-79. (Review) 16. Stary HC, Chandler AB, Dinsmore RE, et al. A definition of advanced types of atherosclerotic lesions and a histological classification of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association. Circulation 1995; 92: 1355-74. (Review) 17. Fujishiro K, Diez Roux AV, Landsbergis P, et al. Associations of occupation, job control and job demands with intima-media thickness: the Multi-Ethnic Study of Atherosclerosis (MESA). Occup Environ Med 2011; 68: 319-26. 18. Rosvall M, Ostergren PO, Hedblad B, Isacsson SO, Janzon L, Berglund G. Work-related psychosocial factors and carotid atherosclerosis. Int J Epidemiol 2002; 31: 1169-78. 19. Greenlund KJ, Kiefe CI, Giles WH, Liu K. Associations of job strain and occupation with subclinical atherosclerosis: The CAR-
650
CHOU, ET AL
DIA Study. Ann Epidemiol 2010; 20: 323-31. 20. Nomura K, Nakao M, Karita K, Nishikitani M, Yano E. Association between work-related psychological stress and arterial stiffness measured by brachial-ankle pulse-wave velocity in young Japanese males from an information service company. Scand J Work Environ Health 2005; 31: 352-9. 21. Utsugi M, Saijo Y, Yoshioka E, et al. Relationship between two alternative occupational stress models and arterial stiffness: a crosssectional study among Japanese workers. Int Arch Occup Environ Health 2009; 82: 175-83. 22. Blacher J, Guerin AP, Pannier B, Marchais SJ, Safar ME, London GM. Impact of aortic stiffness on survival in end-stage renal disease. Circulation 1999; 99: 2434-9. 23. Mitchell GF, Hwang SJ, Vasan RS, et al. Arterial stiffness and cardiovascular events: the Framingham Heart Study. Circulation 2010; 121: 505-11. 24. Yamashina A, Tomiyama H, Takeda K, et al. Validity, reproducibility, and clinical significance of noninvasive brachial-ankle pulse wave velocity measurement. Hypertens Res 2002; 25: 359-64. 25. Tomiyama H, Yamashina A, Arai T, et al. Influences of age and gender on results of noninvasive brachial–ankle pulse wave velocity measurement-- a survey of 12517 subjects. Atherosclerosis 2003; 166: 303-9. 26. Fujiwara Y, Chaves P, Takahashi R, et al. Relationships between brachial-ankle pulse wave velocity and conventional atherosclerotic risk factors in community-dwelling people. Prev Med 2004; 39: 1135-42. 27. Hung CS, Lin JW, Hsu CN, et al. Using brachial-ankle pulse wave velocity to associate arterial stiffness with cardiovascular risks. Nutr Metab Cardiovasc Dis 2009; 19: 241-6. 28. Choi KM, Lee KW, Seo JA, et al. Relationship between brachialankle pulse wave velocity and cardiovascular risk factors of the metabolic syndrome. Diabetes Res Clin Pract 2004; 66: 57-61. 29. Imanishi R, Seto S, Toda G, et al. High brachial-ankle pulse wave velocity is an independent predictor of the presence of coronary artery disease in men. Hypertens Res 2004; 27: 71-8. 30. Vlachopoulos C, Aznaouridis K, Terentes-Printzios D, Ioakeimidis N, Stefanadis C. Prediction of cardiovascular events and all-cause mortality with brachial-ankle elasticity index: a systematic review and meta-analysis. Hypertension 2012; 60: 556-62. (Review) 31. Kitahara T, Ono K, Tsuchida A, et al. Impact of brachial-ankle pulse wave velocity and ankle-brachial blood pressure index on mortality in hemodialysis patients. Am J Kidney Dis 2005; 46: 688-96. 32. Yeh WY, Cheng Y, Chen CJ, Hu PY, Kristensen TS. Psychometric properties of the Chinese version of Copenhagen burnout inventory among employees in two companies in Taiwan. Int J Behav Med 2007; 14: 126-33.
Int Heart J November 2015
33. Yeh WY, Cheng YW, Chen MJ, Chiu AW. Development and validation of an occupational burnout inventory. Taiwan J Public Health 2008; 27: 349-64. 34. Chou LP, Li CY, Hu SC. Job stress and burnout in hospital employees: comparisons of different medical professions in a regional hospital in Taiwan. BMJ Open 2014; 4: e004185. 35. Lee Y, Yang MJ, Lai TJ, Chiu NM, Chau TT. Development of the Taiwanese Depression Questionnaire. Chang Gung Med J 2000; 23: 688-94. 36. Lee Y, Lin PY, Hsu ST, Cing-Chi Y, Yang LC, Wen JK. Comparing the use of the Taiwanese Depression Questionnaire and Beck Depression Inventory for screening depression in patients with chronic pain. Chang Gung Med J 2008; 31: 369-77. 37. Pickering TG, Hall JE, Appel LJ, et al. Recommendations for blood pressure measurement in humans: an AHA scientific statement from the Council on High Blood Pressure Research Professional and Public Education Subcommittee. J Clin Hypertens 2005; 7: 102-9. 38. Cheng Y, Du CL, Hwang JJ, Chen IS, Chen MF, Su TC. Working hours, sleep duration and the risk of acute coronary heart disease: a case-control study of middle-aged men in Taiwan. Int J Cardiol 2014; 171: 419-22. 39. Sparks K, Cooper C, Fried Y, Shirom A. The effects of hours of work on health: a meta-analytic review. J Occup Organ Psychol 1997; 70: 391-408. 40. Overtime and Extended Work Shifts: Recent Findings on Illnesses, Injuries and Health Behaviors. DHHS (NIOSH) 2004-143. Available at: http://www.cdc.gov/niosh/docs/2004-143/pdfs/2004-143. pdf. Accessed August 18, 2015. 41. Virtanen M, Heikkilä K, Jokela M, et al. Long working hours and coronary heart disease: a systematic review and meta-analysis. Am J Epidemiol 2012; 176: 586-96. (Review) 42. Nishiyama K, Johnson JV. Karoshi--death from overwork: occupational health consequences of Japanese production management. Int J Health Serv 1997; 27: 625-41. (Review) 43. Average Annual Hours Actually Worked Per Person in Employment. Available at: http://statdb.mol.gov.tw/html/nat/Table%206-1. pdf. Accessed August 18, 2015. 44. OECD. Average annual hours actually worked per worker. Available at: http://stats.oecd.org/ index.aspx?DataSetCode=ANHRS. Accessed August 18, 2015. 45. Ferrie JE, Shipley MJ, Cappuccio FP, et al. A prospective study of change in sleep duration: associations with mortality in the Whitehall II cohort. Sleep 2007; 30: 1659-66. 46. Tamakoshi A, Ohno Y. Self-reported sleep duration as a predictor of all-cause mortality: results from the JACC study, Japan. Sleep 2004; 27: 51-4.
