Job Strain Has Modest Effect on Heart Disease Risk

September 14, 2012

September 13, 2012 (London, United Kingdom) — Job strain is associated with a small but consistent increased risk of coronary heart disease, according to new research [1]. The study pooled published and unpublished data to generate a cohort of almost 200 000 people, and this "allowed us to investigate the association between CHD and job strain with greater precision than has previously been possible," say Dr Mika Kivimäki (University College London, UK) and colleagues in their paper published online September 13, 2012 in the Lancet.

Kivimäki told heartwire that more than 30 years of research on workplace stress and its link with heart disease have produced mixed results, with some studies finding up to a ninefold increased risk while others found no association. Also, there has been the issue of whether there is a particular subgroup of people who are more adversely affected, he says.

Our finding is that there is an effect of job strain, and although it's fairly modest, it's very robust.

"This study is more than twice the size of the most recent meta-analysis published on this topic; the magnitude is different. Our finding is that there is an effect of job strain, and although it's fairly modest, it's very robust. In addition, we don't see any subgroups that are more vulnerable than any other."

He stressed that it is still not known whether the relationship between job strain and heart disease is causal. But assuming it is, the risk associated with work stress is still "substantially less" than that for other known risk factors for CHD, such as smoking, abdominal obesity, and inactivity, he noted.

A 20% to 30% Increased Risk of Heart Disease Associated With Job Strain

In the collaborative meta-analysis, Kivimäki and colleagues analyzed job strain in employees without CHD at baseline who participated in 13 European national cohorts conducted in Belgium, Denmark, Finland, France, the Netherlands, Sweden, and the UK between 1985 and 2006. All participants completed questionnaires at the start of the studies to assess job demands, excessive workload, the level of time/pressure demands, and freedom to make decisions. Only three of the cohorts had previously published their data, Kivimäki told heartwire .

Of the 197 473 participants, 30 214 (15%) reported job strain. There were 2356 incident CHD events (first nonfatal heart attack or coronary death) during the average 7.5-year course of follow-up.

After adjustment for sex and age, the hazard ratio for job strain vs no job strain was 1.23; this remained the same even after taking into account factors such as lifestyle, age, gender, and socioeconomic status. However, the effect estimate was higher in published (HR 1.43) than in unpublished (1.16) studies, the researchers note.

They then further subdivided job strain into four categories--based on demands and control--and looked at the interplay of these factors. Kivimäki says it looks like the worst kind of job stress "is to have high demands/pressure but little decision authority and so very little say on what goes on at work, and the opportunities to learn are poor."

Accordingly, they found the highest risk of CHD in those who reported high demands and low control (HR 1.28 compared with low demands/high control).

The team also sought to reduce bias owing to reverse causation by exclusion of disease events that occurred in the first three and five years, but this did not seem to have any material effect on their conclusions.

More Sophisticated Analyses of Workplace Stressors Needed

In an accompanying editorial [2], Dr Bo Netterstrøm (Department of Occupational and Environmental Medicine, Copenhagen, Denmark) says the new work is one of the few publications to have analyzed the interaction between demand and control as separate components of job strain.

But Netterstrøm says that the job strain model is now limited, due to societal developments that mean it is only "part of a psychologically damaging work environment and best suited to industrial work." Nevertheless, it "will remain a useful method to assess part of the psychosocial strain in workplaces, especially in the developing world," he adds.

But more sophisticated measures will be needed to better distinguish between different stressors in the workplace in the future, Netterstrøm explains--for example, distinctions between quantitative, cognitive, and emotional demands.

"High work pace is not necessarily a stressor if sufficient time is allowed, and difficult tasks might be a challenge rather than being excessively strenuous if achieved successfully; hence, different types of work will have different strain profiles."

Kivimäki agrees. "Netterstrøm is correct. It is time to look at other workplace exposures. We are now starting to examine things such as job insecurity and the ratio between efforts and reward. If you put a lot of effort into work but receive little reward in terms of satisfaction and salary, that is a bad combination, for example."

The authors and editorialists declare they have no conflicts of interest.