Even in areas with moderate-to-high levels of traffic pollution, regular physical activity reduced the risk of first and recurrent myocardial infarction, according to new research in Journal of the American Heart Association, the Open Access Journal of the American Heart Association/American Stroke Association.

"While exercise is known to reduce cardiovascular disease risk; pollution can increase the risk of cardiovascular disease, including MIs, asthma and chronic obstructive lung disease," said Nadine Kubesch, Ph.D., lead author and researcher at the University of Copenhagen in Denmark. "Currently there is little data on whether poor air quality cancels out the protective benefits of physical activity in preventing MIs."

Researchers in Denmark, Germany and Spain evaluated outdoor physical activity levels (sports, cycling, walking and gardening) and nitrogen dioxide (NO₂ pollutant generated by traffic) exposure in 51,868 adults, age 50-65, comparing self-reported activities and lifestyle factors against MI. Over a 17.7-year period, there were 2,936 first MIs and 324 recurrent MIs.

To estimate average NO₂ exposure, researchers used national traffic pollution monitoring data for each participants' address and found:

• Higher levels of pollution were associated with more MIs, however, the risk was lower among those who were physically active.
• Moderate cycling for four or more hours per week cut risk for recurrent MI by 31 percent; and there was a 58 percent reduction when all four types of physical activity (together totaling four hours per week or more) were combined, regardless of air quality.
• Those who participated in sports had a 15 percent lower rate of initial MIs and there was a 9 percent risk reduction associated with cycling, regardless of air quality
• Compared to participants with low residential NO₂ exposure, those in higher risk areas had a 17 percent increase risk in first MI and 39 percent for recurrent MI.

In participants who developed a first or recurrent MI, the average NO₂  exposure level was 18.9 microgram per cubic meter air (μg/m³) with an overall average of 18.7 μg/m³, which is below the current NO₂ European Union exposure guideline (50 μg/m³ over 24 hours).

"Our study shows that physical activity even during exposure to air pollution, in cities with levels similar to those in Copenhagen, can reduce the risk of MI," Kubesch said. "Our research supports existing evidence that even moderate levels of regular physical activity, such as active commuting, are sufficiently intense to get these health benefits.

Co-authors are Jeanette Therming Jørgensen, M.Sc.; Barbara Hoffmann, M.D.,M.P.H.; Steffen Loft, Ph.D.; Mark J. Nieuwenhuijsen, Ph.D.; Ole Raaschou-Nielsen, Ph.D.; Marie Pedersen, Ph.D.; Ole Hertel, Ph.D.; Kim Overvad, Ph.D.; Anne Tjønneland, M.D., Ph.D.; Eva Prescott, M.D., D.M.Sc.; and Zorana J. Andersen, Ph.D.  The authors report no disclosures.

The Novo Nordisk Foundation, Denmark, funded the study.