In the last few decades, many public health studies have highlighted the necessity of studying unhealthy behaviours such as smoking, drinking, poor diet and sedentary lifestyles [1, 2]. Scholars have observed that smoking, binge drinking, less exercise and poor diet contribute significantly to the high level of morbidity and mortality witnessed in both developed and developing countries [1, 3, 4]. Some risk factors, such as work stress, associated with unhealthy behaviours have not been studied extensively in the past [1, 5]. Even though moderate work stress can motivate people to become more productive, excessive or unmanageable stress may increase their risks of unhealthy behaviours . Research has even shown that when people are not satisfied with their work or do not receive the desired rewards for their efforts, they are more likely to experience work stress .
Two models for work stress evaluation
Two models that are widely used in many epidemiological studies to evaluate the level of work stress include Karasek’s Job Demand-Control (JDC) model and Siegrist’s Effort-Reward Imbalance (ERI) model [8–14]. The JDC model measures the magnitude of work-related stress from job demand and job control dimensions . The model postulates that the most stressed people are those with high job demands combined with low work control [9, 10]. However, at the core of the ERI model, there is the principle of the work contract and social reciprocity . This model predicts that the combination of high efforts and low rewards would significantly increase negative emotions and a high level of work stress .
Reasons for studying the association between work stress and health behaviours in Korea and Japan
Previous research has indicated that health behaviours, including smoking, alcohol consumption, diet and exercise, are likely to be associated with chronic and cardiovascular diseases . In addition, most of the existing studies have focused on European and North American countries, and only a few have examined the association between job stress and health behaviours in East Asian countries [1, 5].
A paper based on two Finnish cohort studies utilised the ERI model to examine the relationship between work stress and smoking and found that highly stressed people were more likely to smoke . Another US study, using the job strain model, produced a similar result and concluded that high strain jobs were positively associated with smoking intensity . In terms of drinking, Siegrist and Rödel, in their meta-analysis of 18 articles, investigated the association between work-related stress and alcohol consumption . They indicated that most of the existing articles have used the JDC model to evaluate work stress, while few articles have used the ERI model . Although a variety of cross-sectional studies failed to determine the association between work-related stress and heavy episodic drinking, some European studies found that work-related stress contributed to chronic heavy drinking and alcohol addiction [18–20].
Middle-aged and older workers in the Asian region are particularly vulnerable to work-related stress [21, 22]. Because of this and lack of relevant policies and welfare systems guaranteeing the rights of employees in Asia, it is predicted that work-related stress might have a more serious impact on employees in East Asian countries than in Western countries [21, 22]. Two developed countries with similar economic development patterns, Japan and Korea, have witnessed an increased rate of work-related deaths in the last three decades [7, 23].
In Korea and Japan, evidence from the analysis of the relationships between work-related stress and health behaviours is limited [24–27]. Kawakami and Haratani pointed out that compared to some European countries, Japanese people felt less satisfied with their jobs, thereby making them more vulnerable to work-related stress . In a Korean cohort study, job security was negatively associated with smoking status among people aged 20-59 . Similarly, in a cross-sectional study conducted in Japan, a considerable number of nurses with high job strains depended on heavy smoking .
Additionally, Japan and South Korea have some similarities when exploring the association between work stress and healthy behaviour; however, no literature has compared the two countries simultaneously. Several Japanese and Korean studies found that a gender difference might exist in the association between work stress and various health outcomes [2, 24, 25, 28]. Lack of intrinsic work rewards and uncertainty about the future contributed to unhealthy behaviours more seriously in males than in females [28, 29]. Moreover, existing evidence suggests that the role of work stress on health behaviours in Japan is similar to that in Korea. According to different cohort and cross-sectional studies, work stress was negatively associated with vegetable intake and positively associated with high calorie intake [30–32]. The results from two Japanese occupational cohort studies showed that high job strain and ER ratio were modestly related to physical inactivity [33, 34]. Previous studies also found that age, gender, education level, marital status, occupational grade, socioeconomic status and working time might be covariates that need to be controlled for when studying the relationship between work-related stress and health behaviours in Korea and Japan [2, 25, 26, 35].
Research gaps in work stress and health behaviours
In summary, past Japanese and Korean work-stress research focused on the relationship between work-related stress and individual health behaviours in some specific occupations, but they had yet to look at several health behaviours in the same analysis in general population samples . Thus, this paper focuses on the association between work stress and two unhealthy behaviours, smoking and heavy alcohol consumption, in Korea and Japan by using two well-known ageing datasets, JSTAR and KLoSA [6, 36]. To focus on a potentially more vulnerable population, the target population of this research is middle-aged and older workers aged 45 years and older in Korea and Japan . To provide a comparative evaluation of work stress in these two potentially different socioeconomic and sociocultural contexts, this study uses the ERI model to assess work-related stress. The short form of ERI used in the KLoSA and JSTAR datasets, previously used and partially validated by Siegrist et al, will be used to measure the ERI model [9, 37, 38]. The Methodology section will provide further details of the variables used in the analysis.
Aims, Objectives and Hypotheses
This study aims to apply the ERI model to evaluate work-related stress and explore its association with the prevalence of smoking and drinking in Korea and Japan among working participants aged 45 years or more. Most importantly, this research aims to examine whether work stress is positively associated with smoking and higher levels of drinking after adjustment for a wide range of available covariates. The study has three objectives: (1) to examine the association between ERI and health behaviours in KLoSA and JSTAR, (2) to investigate the potential interactions between ERI and gender, and (3) to compare results from Korea and Japan and to identify any potential differences in findings.