Should You Exercise Outside in Air Pollution?
Published September 20, 2021
Science has shown the benefits of exercise or physical activity. But what about exercising outside when there is high air pollution, such as smoke from a wildfire or ozone during a hot and sunny day?
The answer is: it depends. The air pollution level, a person’s health status, and the length and intensity of the exercise are all important to consider. Physical activity has long been identified as important to health and is recommended by the U.S. Department of Health and Human Services (HHS). The 2018 HHS guidelines refer to the EPA’s Air Quality Index (AQI) for information about exercising or doing other physical activity when there is air pollution in the forecast.
EPA researchers are working to improve knowledge about the relationship between exercise and air pollution, which, until recently, has not been an active area of research. In 2010, the Centers for Disease Control and Prevention (CDC) held a workshop to review the state of the science and existing public health guidance on physical activity and outdoor air pollution exposure. The international experts attending the workshop recommended additional research to assist with future public health guidance.
Since then, the study of potential health effects of air pollution during exercise has gained in popularity, especially in the last five years, says Stephanie DeFlorio-Barker, an epidemiologist in EPA’s Office of Research and Development. DeFlorio-Barker and colleagues have conducted a systematic scientific review of the literature published between 2000-2020 on the short-term health effects from exposure to air pollution during outdoor exercise.
In their search, they found 25 studies and selected 16 that met their criteria for studying short-term effects and having four distinct study groups — 1) exercising in clean air, 2) exercising in polluted air, 3) resting in clean air and 4) resting in polluted air. This criteria provided a more consistent and scientifically rigorous comparison of results, DeFlorio-Barker says. The review offered challenges because of the wide differences in how research was conducted, the diversity of study groups and the types of health effects studied, she notes.
“The main question we were trying to answer in the review is: Are there worsening health effects among individuals while exercising in polluted air?” says DeFlorio-Barker.
Nine of the 16 papers reviewed demonstrated that exercising outdoors in air pollution results in short-term (temporary) health effects, with lung function impairments being the most observed. The seven other papers, which looked at different health effects, such as inflammation and blood pressure, found no effects.
The study, which is published in the journal Preventive Medicine, showed that healthy people who did moderate to high intensity exercise outdoors in low or high levels of air pollution experienced less health effects than when doing low-intensity exercise. For people with pre-existing conditions such as respiratory or cardiovascular disease, even low-intensity activities like walking may intensify the negative impacts of air pollution, the study suggests.
“Personally, I expected to see that high intensity exercise resulted in worsening effects due to the increased dose of air pollution, but really we found the opposite,” DeFlorio-Barker says. The findings show the need for further study, she adds.
DeFlorio-Barker is conducting a second scientific review that includes almost 70 additional papers, most published within the last two years. While the first review looked primarily at whether there were health effects during exercise in air pollution, the second review is focused on learning more about possible differences in health effects among active and less active people who exercise in air pollution. The research is expected to help inform public health officials on future guidance to the public.