When health benefits of exercise go up in smoke

Exposure to particulate matter (PM) in air pollutants, such as PM2.5 and PM10, has detrimental effects on cardiovascular (CV) diseases. In the direct pathway, fine particles of PM2.5 are directly transmitted into the blood stream and are deposited on target organs, causing vasoconstriction, endothelial dysfunction, elevated blood pressure, and platelet aggregation. In the indirect pathway, PM activates the pulmonary oxidative stress and systemic inflammatory pathways, which contribute to increasing the risk of CV disease. Physical activity (PA) has well-known cardioprotective effects but engaging in outdoor physical activity in a polluted atmosphere might have detrimental effects on CV health due to the increased inhalation of air pollutants. There is little information on the trade-off between the CV health benefits of physical activity and the potential harmful effects of increased exposure to air pollution during outdoor physical activity.

In the current study from South Korea (1) 1,469,972 young adults aged 20–39 years without a previous history of CV disease underwent two consecutive biennial health examinations (2009-2010 and 2011-2012) and then followed up until 2018. The examination included assessment of physical activity as minutes of metabolic equivalent tasks per week (MET-min/week) based on self-administered questionnaire using a last seven-day recall method. Air pollution exposure was estimated by the annual average cumulative level of PM.

There was a significant effect modification of the association between changes in physical activity and cardiovascular disease risk by the level of exposure to PM2.5 or PM10. Physically active young adults who decreased their physical activity had an increased risk of CVD compared with those who maintained their frequency of physical activity within groups with low-to-moderate levels of exposure to PM2.5 or PM10. In contrast, among young adults exposed to high levels of PM2.5 or PM10, participants who increased their physical activity above 1000 MET-min/week were at an increased risk of CV disease.

Personal comment: Air pollution avoidance by limiting outdoor physical activity can help limit air pollution exposure but may bring adverse health effects due to a sedentary lifestyle. Therefore, for individuals who are exposed to high levels of ambient air pollution, engaging in physical activity while reducing exposure to air pollution by methods such as air filtration systems should be encouraged to prevent the negation of the benefits of physical activity to cardiovascular health. It is important to determine the optimal patterns of physical activity behaviours according to air pollution levels because air pollution is an obstacle to active exercise, despite the clinical importance of physical activity. In the future, the decision to take part in outdoor PA or not may depend on the assessment of external environmental exposures, especially in cities, where novel technologies including smartphones, GPS devices, and small sensors could bring advancements.