Individual and Combined Effects of Job Strain Components on Subsequent Morbidity and Mortality : Epidemiology

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Individual and Combined Effects of Job Strain Components on Subsequent Morbidity and Mortality

Kivimäki, Mika; Nyberg, Solja T.; Pentti, Jaana; Madsen, Ida E. H.; Hanson, Linda L. Magnusson; Rugulies, Reiner; Vahtera, Jussi; Coggon, David; on behalf of the IPD-Work consortium*

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doi: 10.1097/EDE.0000000000001020

To the Editor:

In analyses of longitudinal data from 7 to 14 cohort studies, the Individual Participant Data Meta-analysis in Working Populations (IPD-Work) consortium has demonstrated associations of job strain with an increased risk of coronary heart disease (CHD),1 ischemic stroke,2 type 2 diabetes,3 and depression.4 Moreover, among men who already had cardiometabolic disease, job strain carried a 1.6-fold increased risk of death.5 In contrast, no association was evident with other health outcomes, such as cancer, chronic obstructive pulmonary disease, asthma, Crohn’s disease or ulcerative colitis (eAppendix, p. 2; https://links.lww.com/EDE/B507).

In all those analyses, job strain was defined by the combination of high occupational demands with low control,6 and was selected for investigation because, based on psychological theory,7,8 it was expected a priori to trigger harmful stress responses that might cause or promote chronic disease. Some commentators, however, have challenged this predefined approach and questioned the extent to which the observed associations with cardiometabolic outcomes and depression reflect effects specific to job strain, or whether they might be driven by independent effects of high occupational demands or low job control.9

Here we address that concern by presenting further analyses of the IPD-Work datasets. We report separate risk estimates for each combination of occupational demands and control, taking the combination of “neither high demands nor low control” as the reference. A description of the study populations and assessment of outcomes (i.e., CHD,1 ischemic stroke,2 type 2 diabetes,3 depression4, and, among men with cardiometabolic disease, total mortality)5 has been published previously and is summarized in the eAppendix (p. 1–5; https://links.lww.com/EDE/B507).

The Table shows the results of previous IPD-Work studies on job strain as a binary exposure (part A) and those of the present analysis on job strain components (parts B and C). For each outcome, the summary risk estimates for job strain in the current component-specific analysis (part B) were similar in direction and magnitude to those previously published for the binary job strain variable (part A). In addition, age-, sex-, and socioeconomic status-adjusted hazard ratios for high demands with low control (i.e., job strain) were substantially higher than those for high demands in the absence of low control and low control in the absence of high demands (part B).

T1
TABLE.:
Adjusted hazard ratios for the association of binary job strain variable with morbidity and mortality in previous IPD-Work studies (A) and age-, sex-, and socioeconomic status-adjusted hazard ratios for the associations of job strain components with these outcomes (B and C)

Study-specific analyses for incident CHD, ischemic stroke, type 2 diabetes, and clinical depression showed that 38 (83%) of the 46 hazard ratios for job strain versus neither high demands nor low control favored risk factor status (part C). According to I2-statistics, heterogeneity in the study-specific hazard ratios was 0% for all outcomes (eAppendix, p. 5–10; https://links.lww.com/EDE/B507). Consistency of study-specific findings was poorer for high demands in the absence of low control (24/46 [52%], max I2 = 19%) and low control in the absence of high demands (30/46 [65%], max I2 = 53%). Small sample size precluded study-level comparisons for mortality in men with cardiometabolic disease.

In conclusion, findings of cohort studies from the United Kingdom, France, Belgium, Denmark, Sweden, and Finland indicate that for each of CHD, ischemic stroke, type 2 diabetes, depression and (among men with cardiometabolic disease) mortality, risks are highest in individuals with job strain, whereas any effects of high occupational demands in the absence of low control, and of low job control in the absence of high demands, were weaker. Job strain defined as the combination of high job demands and low control is consistent with more general definitions of psychological stress which suggest that stress occurs when demands from external situations are perceived to be beyond coping capacities.7 As such, our results support the psychological stress theory underpinning our a priori decision to examine job strain as a binary risk factor for morbidity and mortality.

Mika Kivimäki
Department of Epidemiology and Public Health
University College London
London, United Kingdom
Clinicum, Faculty of Medicine
University of Helsinki
Helsinki, Finland
Finnish Institute of Occupational Health
Helsinki, Finland
[email protected]

Solja T. Nyberg
Clinicum, Faculty of Medicine
University of Helsinki
Helsinki, Finland

Jaana Pentti
Clinicum, Faculty of Medicine
University of Helsinki
Helsinki, Finland
Department of Public Health
University of Turku
Turku, Finland

Ida E. H. Madsen
National Research Centre for the Working Environment
Copenhagen, Denmark

Linda L. Magnusson Hanson
Stress Research Institute
Stockholm University
Stockholm, Sweden

Reiner Rugulies
National Research Centre for the Working Environment
Copenhagen, Denmark
Department of Public Health
University of Copenhagen
Copenhagen, Denmark
Department of Psychology
University of Copenhagen
Copenhagen, Denmark

Jussi Vahtera
Department of Public Health
Turku University Hospital
University of Turku
Turku, Finland

David Coggon
MRC Lifecourse Epidemiology Unit
University of Southampton
Southampton, United Kingdom
on behalf of the IPD-Work consortium*

REFERENCES

1. Kivimäki M, Nyberg ST, Batty GD, et al.; IPD-Work Consortium. Job strain as a risk factor for coronary heart disease: a collaborative meta-analysis of individual participant data. Lancet. 2012;380:1491–1497.
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5. Kivimäki M, Pentti J, Ferrie JE, et al.; IPD-Work consortium. Work stress and risk of death in men and women with and without cardiometabolic disease: a multicohort study. Lancet Diabetes Endocrinol. 2018;6:705–713.
6. Karasek R. Job demands, job decision latitude, and mental strain: implications for job redesign. Adm Sci Q. 1979;24: 287–308.
7. Lazarus RS. Psychological Stress and the Coping Process. 1966.New York, NY: McGraw-Hill.
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9. Mikkelsen S, Andersen JH, Ingre M. Re: effort-reward imbalance at work and incident coronary heart disease. Epidemiology. 2018;29:e35.

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