The role of working conditions in educational differences in ischemic heart disease mortality

BACKGROUND: The educational gradient in cardiovascular mortality is well established, but still not completely understood. One important mechanism may be working conditions. This study aims to investigate the extent to which job control and heavy physical workload explain educational differences in ischemic heart disease (IHD) mortality while also accounting for risk factors established in childhood and adolescence. METHODS: This register-based cohort study is based on men who completed their mandatory conscription (age 18-20) for the Swedish military in 1969/1970. This includes 37,419 men who also had a registered occupation in 2005. IHD mortality was measured in the cause of death register. Educational differences in IHD mortality, followed between 2006 and 2019, were measured using Cox proportional hazards regression models. Models were first adjusted for socioeconomic, cognitive, health and behavioral factors measured in childhood and during conscription. Models were further adjusted for physical workload and job control in 2005 (measured during mid-50s). These occupational exposures were measured using Job Exposure Matrices (JEM). Percent attenuation in hazard ratios (HR) after adjustment were calculated using the formula ((HR crude-HR adjusted)/(HRcrude-1))*100. RESULTS: Crude models showed a clear educational gradient regarding IHD mortality (HR 2.67, 95% confidence interval 2.08-3.42 for the lowest educated compared to the highest educated). Adjusting for earlier risk factors resulted in a 39-50% reduction in HR estimates. Further adjusting for physical workload and job control resulted in around 75% reductions compared to the crude model. CONCLUSIONS: Physical workload and job control explained around 25% of the increased risk of IHD mortality in those with lower education. Improvement of the physical and psychosocial work environment could lead to a reduction in IHD mortality and smaller educational differences. KEY MESSAGES: • Physical workload and job control played an important role in educational differences in IHD even when accounting for a variety of early life risk factors. • Improving the physical and psychosocial work environment could lead to a lower incidence of IHD deaths and reduced educational inequalities.