The effects of commuting activity and occupational and leisure time physical activity on risk of myocardial infarction.

BACKGROUND: Risk reduction of myocardial infarction has been shown for leisure time physical activity. The results of studies on occupational physical activity and risk of myocardial infarction are incongruous and studies on commuting activity are scarce. The aim of this study was to investigate how commuting activity, occupational physical activity and leisure time physical activity were associated with risk of future first myocardial infarction.
DESIGN: We used a prospective incident case-referent study design nested in Västerbotten Intervention Program and the Northern Sweden MONICA study.
METHODS: Commuting habits, occupational physical activity, leisure time physical activity and cardiovascular risk factors were assessed at baseline screening and compared in 583 cases (20% women) with a first myocardial infarction and 2098 matched referents.
RESULTS: Regular car commuting was associated with increased risk of myocardial infarction versus commuting by bus, cycling or walking [odds ratio (OR) 1.74; 95% confidence interval (CI), 1.20-2.52] after multivariate adjustment. High versus low leisure time physical activity was associated with reduced risk of myocardial infarction (OR 0.69; 95% CI, 0.50-0.95) after adjustment for occupational physical activity and commuting activity, but the association was not statistically significant after further multivariate adjustment. After multivariate adjustment we observed a reduced risk for myocardial infarction in men with moderate (OR 0.70; 95% CI, 0.50-0.98) or high (OR 0.67; 95% CI, 0.42-1.08) versus low occupational physical activity.
CONCLUSIONS: We found a clear association between car commuting and a first myocardial infarction and a corresponding inverse association with leisure time physical activity, while the impact of occupational physical activity on the risk of myocardial infarction was weaker.