Self-assessed job satisfaction and ischaemic heart disease mortality: a 10-year follow-up of urban bus drivers

Several studies have shown that bus driving is a high-risk occupation for ischaemic heart disease (IHD). In order to study contributing factors in the job, all male full-time bus drivers in the three major cities in Denmark were followed for 10 years. It was hypothesized that bus drivers who reported job strain and job dissatisfaction would have an excess risk of subsequent death due to IHD. Of 2465 bus drivers, 2045 (83%) responded to a questionnaire distributed in 1978 on psychosocial well-being and work conditions. The men had their mortality recorded during the years 1978-1988. Information on causes of death was obtained from the Danish Register of Causes of Death. Some 212 respondents died during the follow-up period, 59 from IHD. Relative risk (RR) for death due to IHD and all other causes of death was calculated. As expected, we found a significantly increased risk of IHD in bus drivers working in a high traffic intensity area, RR = 1.6. In contrast to what was expected, men who reported a high degree of job satisfaction had increased risk of IHD. Those who did not look for another job had a highly significant sixfold increased risk of future death from IHD. Also those who reported never experiencing mental exhaustion after work, that their job was very varied, that their job was something special, and those who reported that they would choose the same job again, had an excess risk. Death due to other causes was positively associated with marital status only. We suggest that inconsistencies in the literature on self-assessed job strain and risk of IHD may be partly explained by the fact that studies in general have focused on absence or presence of the psychosocial factor in question. A more differentiated assessment of exposure might prove more useful.