Job strain and ischaemic disease: does the inclusion of older employees in the cohort dilute the association? The WOLF Stockholm Study.
OBJECTIVE
Evidence on the association between job strain and ischaemic disease is mixed. This study examined whether including older age individuals in a cohort used to assess job strain attenuates findings towards the null.


METHODS
A prospective cohort study with baseline screening in 1992-5. A follow-up for ischaemic disease until 2003 was based on linkages to national registries. Ischaemic disease was corroborated by objective criteria (hospitalisation as a result of acute myocardial infarction, unstable angina or ischaemic stroke; or death from ischaemic heart disease, cardiac arrest or ischaemic stroke).


METHODS
3160 male employees aged 19-65 years without pre-existing or current ischaemic disease.


RESULTS
93 cases of incident ischaemic disease were recorded. In the 19-55 year age group, the participants with job strain had a 1.76 (95% CI 1.05 to 2.95) times higher age-adjusted risk of incident ischaemic disease than those free of strain. Further adjustment for conventional cardiovascular risk factors had little effect on this association, but the impact of job strain was reduced by 70% to non-significant after the inclusion of employees older than 55 years in the cohort (hazard ratio 1.22, 95% CI 0.75 to 1.96).


CONCLUSIONS
Including older employees in a cohort may dilute the effect of job strain on cardiovascular disease and is a potential reason for inconsistent findings in previous studies.
Kivimäki
M
M
International Institute for Society and Health, Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London WC1E 6BT, UK. m.kivimaki@ucl.ac.uk
Theorell
T
T
Westerlund
H
H
Vahtera
J
J
Alfredsson
L
L
D000328:Adult; D017677:Age Distribution; D004522:Educational Status; D004812:Epidemiologic Methods; D015444:Exercise / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000453:epidemiology / Q000523:psychology*; D009784:Occupational Diseases / Q000523:psychology*; D012907:Smoking / Q000453:epidemiology; D012923:Social Class; D013315:Stress, Psychological / Q000150:complications*; D013548:Sweden