J Occup Health 2009; 51: 107–113
Journal of
Occupational Health
Job Stress and Coronary Heart Disease: A Case-control Study using a Chinese Population
Weixian XU1, Yiming ZHAO2, Lijun GUO1, Yanhong GUO1 and Wei GAO1
1Department of Cardiology, Peking University Third Hospital and Key Laboratory of Molecular Cardiovascular Science, Ministry of Education and 2Research Center of Occupational Medicine, Peking University Third Hospital, China
Abstract: Job Stress and Coronary Heart Disease: A Case-control Study using a Chinese Population: Weixian XU, et al. Department of Cardiology, Peking University Third Hospital and Key Laboratory of Molecular Cardiovascular Science, Ministry of Education, China— Objectives: This study was to examine the association between job stress and coronary heart disease (CHD) in a Chinese population. Methods: The 388 participants aged 30 to 70 yr who received coronary angiography for suspected or known ischemic heart disease were enrolled in this series, which included 292 CHD cases and 96 controls. The job stress before CHD onset was measured by the effort-reward imbalance (ERI) model. Results: In the results, compared with the baseline, high ERI, high extrinsic effort or high overcommitment increased the risk of CHD with odds ratios (OR) of 2.8, 2.7 and 2.8 respectively after adjustment for the traditional CHD risk factors, such as age, gender, primary hypertension, diabetes mellitus, hyperlipidemia, smoking, body mass index, CHD family history, educational level, and marital status. The combination of high ERI and high overcommitment led to the highest risk of CHD with adjusted OR 5.5. However, high reward reduced the risk of CHD with an adjusted OR of 0.4 in comparison to low reward. Dose-response relationships were also observed. Conclusions: Job stress evaluated by the ERI model significantly increased the risk of CHD, and it may be an important risk factor independent of the traditional risk factors of CHD in the Chinese population.
(J Occup Health 2009; 51: 107–113)
Key words: Coronary artery disease, Job stress, Risk
Received May 3, 2008; Accepted Nov 14, 2008
Published online in J-STAGE Jan 30, 2009
Correspondence to: W. Gao, Department of Cardiology, Peking University Third Hospital and Key Laboratory of Molecular
Cardiovascular Science, Ministry of Education, No.49, North Garden Road, Beijing 100191, P.R. China
(e-mail: dr_gaowei@medmail.com.cn)
factors
With the development of economic globalization and rising competition, job stress has attracted increasing public concern in the developed countries. The effort-reward imbalance (ERI) model1) is one of the most widely used models for evaluating job stress and includes three scales: extrinsic effort, reward and overcommitment. It has been documented that job stressors evaluated by the ERI model may be important new risk factors for coronary heart disease (CHD)2–10). Peter et al.2) reported job stress was associated with myocardial infarction in the retrospective SHEEP study. In the prospective Whitehall II cohort study, Kuper et al.9) found job stress increased the risk of CHD. Kivimäki et al.10) also reported the same results in a meta-analysis. However, most of the studies were conducted in Western societies. Studies of this issue in Asia are still at the starting stage except in Japan11). Today, due to rapid industrialization China is regarded as the “world’s factory”, and stress at work has become a risk factor which threatens the health of Chinese workers12, 13). CHD is the leading cause of death in the world. Mortality rates of CHD have been halved in many developed countries since the 1980s, but are still rising in most developing countries, including China14). Meanwhile, the knowledge about the association between job stress and CHD in the Chinese population is limited. Jian Li et al. developed the Simplified Chinese Version of the Effort-Reward Imbalance Questionnaire (C-ERIQ) based on the ERI model, and found that C-ERIQ was a reliable and valid instrument for measuring psychosocial stress at work in Chinese working populations15, 16). Xu17) reported job stress was associated with the systolic blood pressure of Chinese working women. However, Asian study has yet examined the association between ERI and CHD. Furthermore, previous studies were limited by assessment of recent job stress at only one point in time and an outcome dependent on the subjective experience
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of CHD symptoms leading to their underestimation or over-estimation18). Therefore, the purpose of the present study is to assess the association between job stress and CHD in a Chinese population.
Methods
Subjects
Four hundred consecutive patients aged 30 to 70 yr with chest pain, who had a full time job for more than 5 yr, underwent coronary angiography for suspected or known ischemic heart disease at Peking University Third Hospital from October 2005 to December 2006. This hospital is the largest comprehensive hospital in the Haidian District of Beijing. It is also an appointed hospital for coronary angiography under medical insurance, and the patients who need coronary angiography in this area attend this hospital. Therefore this sample was representative of coronary angiography patients. Twelve patients were excluded because they had cardiac diseases such as valvular (7 patients), congenital (1 patient), or pericardial diseases (1 patient) or myocardiopathy (3 patients). The final sample size was 388 (the participation rate of the patients was 97%) with various occupations. Their mean age was 55.5 yr old and 75.5% of the population was male. Among the sample, 320 patients underwent coronary angiography for the first time and 68 patients had received it more than once. This study was in accordance with Declaration of Helsinki and all patients provided their informed consent.
Diagnosis of coronary heart disease
The diagnosis of CHD was based on the coronary artery angiography and the clinical manifestation. The assessment of coronary arteries was done by physicians who didn’t take part in the research and were blind to the patients’ job stress levels. Coronary artery luminal stenosis was assessed in accordance with the American Heart Association method19). CHD cases were defined as a 50% or greater luminal stenosis of one or more major coronary arteries, and the patients with normal or less than 50% stenosis of all arteries and without the typical ischemic manifestation were defined as controls.
Procedures
A questionnaire based interview elicited details of job stressors, medical and family history, and lifestyle factors. The interview was done by a research physician face-to-face with every patient. The interviewer was blind to the results of the coronary angiography. First, the patients were requested to list all the full time job titles before the first occurrence of a symptom or an abnormal clinical test suggestive of CHD. Then, the patients described the job stressors in general and completed the ERI questionnaire. If there was more than one job title and job stress level largely varied, the patients were asked to
J Occup Health, Vol. 51, 2009
report the status of the relatively more stressful job title. To reduce potential information bias, the interviewer sat with each patient and explained the questions which the patient did not understand clearly during the time they completed the questionnaire. Finally, the interviewer reviewed the questionnaire and questioned the patients about any inconsistent information to make sure that the information was an accurate reflection of the patient’s job characteristics.
Job stressors
Job stressors were assessed in accordance with Siegrist’s ERI questionnaire (ERI-Q) whose validated Chinese version was developed by Li et al15, 16). The 23-item ERI-Q consists of three scales termed extrinsic effort representing job demands imposed on the employee (6 items), reward which consists of income, respect, job security and career opportunities (11 items), and overcommitment which defines a set of attitudes, behaviors, and emotions reflecting excessive striving in combination with a strong desire for approval and esteem (6 items). The response to each item of the effort scale is scored on 5-point scale, in which the value increases with rising stress level; that is, a value of 1 indicates no respective stressful experience, and a value of 5 indicates a very high stressful experience. Each item of the reward scale is also scored on 5-point scale, in which the value increases with reward level; that is, a value of 1 indicates very low reward, and 5 indicates very high reward. Each item of overcommitment is scored on a 4-point scale (1=full disagreement, 4=full agreement with statement). Cronbach’s coefficients of effort, reward, and overcommitment were 0.67, 0.72, and 0.84, respectively.
The relation between the two scales of extrinsic effort and reward (equally weighted) , that is effort-reward imbalance (ERI), is calculated to quantify the degree of m i s m a t c h b e t w e e n h i g h c o s t a n d l o w g a i n (ERI=11*effort/6*reward) . The subjects were respectively grouped into one of three strata (low, intermediate, or high) for each job stressor based on tertiles defined according to the distribution of scores: 6–11, 12–15, 16 or greater, for extrinsic effort; 30–47, 48–52, 53 or greater, for reward; 8–13, 14–17, 18 or greater for overcommitment; 0.20–0.42, 0.43–0.58, 0.59 or greater, for ERI. Moreover, the combination of high level ERI and high level overcommitment was defined as high ERI*OVC, and the combination of low ERI and low overcommitment as low ERI*OVC, and all other combinations as intermediate ERI*OVC.
Traditional CHD risk factors
Traditional CHD risk factors were also collected. Laboratory data and medical treatments regarding primary hypertension, diabetes mellitus and hyperlipidemia were extracted from medical records. History of hy