ArticlesJob strain as a risk factor for coronary heart disease: a collaborative meta-analysis of individual participant data
Introduction
Investigators have examined the role of psychological factors, such as personality type, cognition, and psychological stress, in the cause of coronary heart disease. Of these factors, psychosocial stress is the most commonly investigated.1, 2, 3 Job strain—the combination of high job demands and low control at work—is one of the most widely studied definitions of psychosocial stress.2 Although some studies4, 5, 6 have shown that job strain is associated with a more than doubling in risk of coronary heart disease, findings from a meta-analysis7 of cohort studies suggest that this excess risk is probably modest, at about 40%. Moreover, the importance of job strain as a risk factor for coronary heart disease continues to be debated because of several methodological shortcomings.
The first limitation is publication bias—ie, studies with significant results in the expected direction are more likely to be published and cited in scientific literature than are those with non-significant findings.8 Second, in studies9, 10 of working hours (job demand), evidence shows that people spontaneously reduce their hours in the years before cardiac events, probably as a response to symptoms of advanced underlying disease. This action could result in perceptions of reduced job demands, which might contribute to reverse causation bias—ie, coronary heart disease affects levels of stress, rather than vice-versa. Exclusion from analysis of coronary heart disease events that occur in the first years of follow-up can reduce such bias, but few studies have been sufficiently powered to do this analysis.
We did a collaborative meta-analysis of individual participant data from published and unpublished studies of job strain and coronary heart disease to address the limitations of previous studies and the discordant evidence base.
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Study population
We used data from 13 independent cohort studies started between 1985 and 2006, in Finland, Sweden, Denmark, the Netherlands, Belgium, France, and the UK.11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 All studies were part of the individual-participant-data meta-analysis in working populations (IPD-Work) consortium, which was established at the Four Centres meeting in London, in 2008.24 Details of the study design and participants have been previously published (appendix).
Our analyses were
Results
We excluded from analyses 5124 (3%) of 203 816 participants who had missing data for age, sex, job strain, or incident coronary heart disease events, and 1219 (1%) with a diagnosis of coronary heart disease before the study baseline. Thus, 197 473 participants were included in the analysis (table). Mean age at study entry was 42·3 years (SD 9·8) and half of participants were women. Dependent on the study, between 13% and 22% of participants had job strain (table).
During 1 488 728 person-years
Discussion
The pooling of published and unpublished studies allowed us to investigate the association between coronary heart disease and exposure to job strain with greater precision than has previously been possible. Our findings suggest that job strain is associated with a small, but consistent, increased risk of an incident event of cardiovascular heart disease. Adjustment for lifestyle and conventional risk factors, and for age, sex, and socioeconomic status, did not substantially change the magnitude
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