Between 1981-1995, 44 studies were published, most of which
found a significant positive relationship between job strain and
CVD or all-cause mortality or job strain and CVD risk factors,
such as hypertension. (Thirty-six of these studies were reviewed
in Schnall, Landsbergis and Baker, 1994, while an additional eight
studies are included in this summary.)
Major early studies had to rely upon available national data bases
in Sweden (49, 50, 54) and the U.S. (59) to link job characteristics
with CVD. More recent studies have tended to focus on CVD risk
factors (primarily elevated blood pressure) in smaller- scale
studies in Sweden (e.g., 109, 114) and the U.S. (10, 75, 99- 101,
116) in which both individual-level exposure and outcome data
were collected.
Estimates of relative risk for men in cohort studies with positive
results have ranged from 1.6 for all-cause mortality among 477
retired Swedish men followed for six years (25), to 1.9 for CVD
mortality among a representative sample of 7219 Swedish male employees
followed for nine years (50), to 6.2 for 79 male Swedish myocardial
infarction (MI) survivors followed for 6-8 years (115). A relative
risk of 2.9 for coronary heart disease (CHD) among 328 women followed
for 10 years, was observed in the Framingham Heart Study (68).
Positive associations were found among cross-sectional, case-
control, and cohort studies. Half of the 44 studies were population-based
which enables generalizability of results. In addition, significant
associations were found with a variety of formulations of the
independent variable (job strain).
Of 12 cohort studies (10 of CVD and two of all-cause mortality),
seven found significant associations (5, 8, 25, 33, 50, 68, 115).
The Alterman et al. (1994) cohort study, while classified as non-confirmatory,
provides results that are nearly significant: OR=1.40 (95% CI
0.92-2.14) for job strain controlling for CVD risk factors. Only
after controlling for occupational status (blue-collar vs white-collar)
does the OR drop to 1.03. Blue-collar status was strongly associated
with job strain. However, while decision latitude was significantly
associated with reduced risk, psychologic demand was also associated
with reduced risk. The methodology of the non-confirmatory Hlatky
et al. (1995) cohort study has been reviewed and criticized [attach
letters to Circulation].
Four studies examined job strain and CVD symptoms while 20 studies
examined job strain and CVD risk factors. While null results were
reported for job strain and serum cholesterol (37, 86, 90, Alterman
et al., 1994), job strain was associated with smoking in three
(32, 81, Johannson, Johnson and Hall, 1991) of seven studies.
In one of these studies, (Alterman et al., 1994), while "job
strain" was not associated with smoking, smoking was associated
with lower demands (p=.058, crude) and lower decision latitude
(p<.001, crude).
Of eight studies of job strain and blood pressure measured in
a clinic setting (3, 19, 37, 75, 79, 86, 90, 116, Alterman et
al., 1994), in which typically only a few casual readings are
taken, only one (37) found a significant association. However,
ambulatory blood pressure monitors give both a more reliable measure
(there is no observer bias and the number of readings is increased)
and a more valid measure of average blood pressure (since blood
pressure is measured during a person's normal daily activities)
than casual measures of blood pressure (89). Of nine job strain
studies utilizing ambulatory blood pressure, five yielded significant
positive results (99, 101, 108, 109, 116), while the remaining
four yielded a mixture of positive and null results (38, 75, 113,
114). These studies, taken as a whole, suggest job strain acts,
in part, to cause CVD through the mechanism of elevated blood
pressure.
Workplace social support has been added to the job strain model
as a third major job characteristic in several studies of CVD
(8, 25, 49, 50, Johannson, Johnson and Hall, 1991; Hall, Johnson
and Tsou, 1993), as well as a number of studies of psychological
strain outcomes (e.g., 60, 71). The combination of job strain
and low social support has been labeled "iso-strain",
or "isolated high strain" work. Only one study (50)
directly examined "iso-strain" as a risk factor. Among
7219 employed Swedish men followed for nine years, "iso-strain"
was associated with CVD morbidity and mortality.
In other studies, the main effect of low social support on CVD
was examined (with positive associations, 25, 49), as well as
the interaction between social support and job strain (8, 25,
49). Social support was as an effect modifier in the Swedish study
of retired men (25) (increased job strain-mortality risk ratios
for those with low social support), in the Swedish factory worker
study (8) (reduced high latitude-mortality risk ratios for those
with high workplace social support), and in a Swedish national
study (49) (increased high demand-low latitude-CVD prevalence
ratios with greater workplace social isolation).
One study (Johannson, Johnson and Hall, 1991) found an association
between smoking and co-worker support, but only for women. However,
no studies of the relation between social support, job strain
and blood pressure have been reported.
References
All numbered references are from: Schnall
PL, Landsbergis PA, Baker D. Job strain and cardiovascular disease.
Annual Review of Public Health; 15:381-411,1994.
Alterman T, Shekelle RB, Vernon SW, Burau KD. Decision latitude,
psychologic demand, job strain and coronary heart disease in the
Western Electric Study. American Journal of Epidemiology 1994;139:620-7.
Braun S, Hollander R. A study of job stress among women and men
in the Federal Republic of Germany. Health Education Research
1987;2:45-51.
Hall EM, Johnson JV, Tsou T-S. Women, occupation, and risk of
cardiovascular morbidity and mortality. Occupational Medicine:
State of the Art Reviews 1993;8:709-19.
Hlatky MA, Lam LC, Lee KL, Clapp-Channing NE, Williams RB, Pryor
DB, Califf RM, Mark DB. Job strain and the prevalence and outcome
of coronary artery disease. Circulation 1995;92:327-333.
Johansson G, Johnson JV, Hall EM. Smoking and sedentary behavior
as related to work organization. Soc Sci Med 1991;32:837-846.
Schnall PL, Landsbergis PA, Baker D. Job strain and cardiovascular
disease. Annual Review of Public Health 1994;15:381-411.
Suadicani P, Hein HO, Gyntelberg F. Are social inequalities as
associated with the risk of ischaemic heart disease a result of
psychosocial working conditions? Atherosclerosis 1993;101:165-75.