The risk of acute myocardial infarction - Interactions of types of physical activity

Background: Leisure time physical activity has previously been shown to be protective against cardiovascular disease. We estimated the influence of exercise, occupational physical activity, and household work with regard to risk of acute myocardial infarction (MI). Special interest was focused on potential interaction among these aspects of physical activity. Method: We analyzed data from a large population-based case-control study conducted in Stockholm, Sweden, 1992-1994. Cases comprised 1204 men and 550 women, age 45-70 years, who experienced their first MI during the study period. The controls, 1538 men and 777 women, were randomly selected from the study base, matched on sex, age, and hospital catchment area. The results were adjusted for several potential confounding factors. Results: Exercise, walking or standing at work, and doing demanding household work were all associated with decreased risk of acute MI; the estimated relative risks (RRs) ranged from 0.31 to 0.90 when all cases (fatal and nonfatal) were considered. In contrast, lifting or carrying at work, and an occupational workload perceived to be strenuous, were related to an increased risk of MI (RRs ranging from 1.10-1.57). We observed a synergistic benefit from exercise and walking or standing at work, and from household work and walking or standing at work. Conclusion: Aerobic physical activities such as exercise or walking at work seemed to reduce the risk of MI, whereas anaerobic activities such as heavy lifting at work were related to increased risk of MI.