IS THE EFFECT OF JOB STRAIN ON MYOCARDIAL-INFARCTION RISK DUE TO INTERACTION BETWEEN HIGH PSYCHOLOGICAL DEMANDS AND LOW DECISION LATITUDE -RESULTS FROM STOCKHOLM-HEART-EPIDEMIOLOGY-PROGRAM (SHEEP)

The objectives are to examine if the excess risk of myocardial infarct ion from exposure to job strain is due to interaction between high dem ands and low control and to analyse what role such an interaction has regarding socioeconomic differences ir. risk of myocardial infarction. The material is a population-based case-referent study having inciden t first events of myocardial infarction as outcome (SHEEP: Stockholm H eart Epidemiology Program). The analysis is restricted to males 45-64 yr of age with a more detailed analysis confined to those still workin g at inclusion. In total, 1047 cases and 1450 referents were included in the analysis. Exposure categories of job strain were formed from se lf reported questionnaire information. The results show that high dema nds and low decision latitude interact with a synergy index of 7.5 (95 % C.I.: 1.8-30.6) providing empirical support for the core mechanism o f the job strain model. Manual workers are more susceptible when expos ed to job strain and its components and this increased susceptibility explains about 25-50% or the relative excess risk among manual workers . Low decision latitude may also,as a causal link, explain about 30% o f the socioeconomic difference in risk of myocardial infarction. The d istinction between the interaction and the causal link mechanisms iden tifies new etiologic questions and intervention alternatives. The spec ific causes of the increased susceptibility among manual workers to jo b strain and its components seem to be an interesting and important re search question. (C) 1998 Elsevier Science Ltd. All rights reserved.