Background: Regular physical activity is inversely associated with risk of coronary heart disease, but the precise mechanisms remain unclear. Active commuting is an environmental friendly way to achieve the recommended 30 min of daily physical activity. The aim of this study was to explore the relative contribution of markers from different potential mediating pathways on the association between active commuting and risk of myocardial infarction (MI) in a general population.
Design: Prospective incident nested case-control study.
Methods: Commuting habits, traditional risk factors and biomarkers were assessed at baseline and compared in 204 MI cases and 327 matched controls.
Results: Car commuting was significantly associated with MI risk, even after adjusting for potential confounders (odds ratio: 1.77, 95% confidence interval: 1.05-2.99). When potential mediators were included in the model, the risk was substantially attenuated. Among the traditional risk factors, apolipoprotein B/apolipoprotein A-1 ratio seemed to be the largest mediator (26.0%), followed by body mass index (18.7%). The inflammatory and haemostatic markers similarly dampened the effect, with tissue plasminogen activator/plasminogen activator inhibitor-1 complex and IL-6 explaining 33.6 and 27.6% of MI risk, respectively. Combined, the potential mediators investigated seemed to explain 40.1% of MI risk related to car commuting.
Conclusion: Overall, the traditional, inflammatory and haemostatic markers seemed to explain a substantial proportion of the reduction in MI risk related to active commuting in this study population. The predominant effect of the inflammatory and haemostatic markers supports the hypothesis that regular physical activity may work through additional biological mechanisms to reduce coronary risk beyond traditional risk factors. However, these findings need to be confirmed in larger studies.