Even at high air pollution, physical activity pays off for MI prevention
Effects of Leisure-Time and Transport-Related Physical Activities on the Risk of Incident and Recurrent Myocardial Infarction and Interaction With Traffic-Related Air Pollution: A Cohort StudyKubesch NJ, Therming Jørgensen J, Hoffmann B, et al. - J Am Heart Assoc. 2018;7:e009554
Introduction and methods
Physical activity reduces the risk of cardiovascular (CV) disease through several mechanisms, including improvements in inflammatory status, hemostatic factors, insulin sensitivity, and blood lipids . Outdoor air pollution, on the other hand, leads to worsening of inflammatory status and oxidative stress, and is therefore a CV risk factor . Physical activity in areas with air pollution may increase exposure to pollutants due to exercise-induced higher minute ventilation, leading to higher deposition of the inhaled particles in the lungs . However, it is not known whether the benefit of physical activity on CV risk is reduced by exposure to air pollution.
This analysis of the Danish Diet, Cancer, and Health cohort , evaluated the effects of physical activity on the risk of incident and recurrent myocardial infarction (MI) in middle-aged men and women, and assessed whether air pollution modifies the association between physical activity and MI.
The Danish Diet, Cancer, and Health cohort included 57,053 individuals with or without a history of MI, aged 50-64 years, between 1993 and 1997. Individuals with a history of cancer and missing data of interest were excluded for this analysis, leaving a study sample of 51,868 participants. Physical activity (sports, cycling, walking, and gardening) was reported in hours per week (h/wk) using a validated questionnaire , and NO2 exposure was estimated for the residential addresses of participants using the Danish AirGIS dispersion modeling system , and classified into low (<14.3 lg/m3), medium (≥14.3–21.0 lg/m3), and high (≥21.0 lg/m3) exposure.
- Of participants without a history of MI at baseline (97.6% of total cohort), 2,936 participants developed incident MI during a mean follow-up of 17.8 years (902,192 person-years), and of those with a history of MI at baseline (2.4%) 324 had a recurrent MI during a mean follow-up of 14.4 years (16,515.88 person-years).
- Of all participants, 54% participated in sports (on average 2.4 h/wk), 68% cycled (on average 3.2 h/wk), 74% gardened (on average 3.0 h/wk), and 93% walked (on average 4.3 h/wk).
- In a fully adjusted model(for occupational physical activity, lifestyle and risk factors), the associations between sports (HR: 0.85; 95%CI: 0.79–0.92) or cycling (HR: 0.91; 95%CI: 0.84–0.98) and incident MI were attenuated, while the association between gardening and MI was strengthened (HR: 0.87; 95%CI: 0.80–0.95).
- Individuals with a history of MI at baseline showed non-significant associations between cycling, walking, gardening, sports participation and recurrent MI.
- Sports participation for 0.5-4 and >4 h/wk reduced the risk for incident MI by 14% and 18%, respectively (HR: 0.86; 95%CI: 0.79-0.93; HR: 0.82; 95%CI: 0.70–0.96), compared with no participation in sports (defined as <0.5 h/wk). Similar results were found for gardening, walking, and cycling.
- The four physical activities combined were associated with reduced risk of recurrent MI with 0.5-4 h/wk (HR: 0.47; 95%CI: 0.24–0.89) and >4 h/wk (HR: 0.42; 95%CI: 0.23–0.78), compared with no physical activity (<0.5 h/wk).
- Living in areas with high NO2 concentrations was positively associated with incident MI (adjHR: 1.17, 95%CI: 1.05-1.30), as compared with areas with low NO2 concentrations. Those with a history of MI showed a higher risk of recurrent MI in areas with high NO2 concentrations (adjHR: 1.39, 95%CI: 1.01-1.93).
- The association between incident or recurrent MI and participation in physical activities was not significantly modified by residential NO2 at baseline, and the preventive effects of physical activity were independent of NO2 after adjustment.
- In areas with medium and high residential NO2 concentrations, inverse associations were seen between sport and incident MI (medium: HR: 0.87, 95%CI: 0.78-0.97, high: HR: 0.79, 95%CI: 0.76-0.95), and between cycling and incident MI at medium NO2 concentration (HR: 0.85, 95%CI: 0.76-0.95). At higher residential NO2 exposure, cycling was inversely associated with recurrent MI (HR: 0.54, 95%CI: 0.34-0.86).
Physical activity, even at moderate levels, reduces the risk of incident and recurrent MI, independently of the exposure to NO2. These results suggest that the long-term benefits of physical activity in primary and secondary MI prevention outweigh the risks associated with exposure to air pollution.