Like I totally agree with encouraging exercise most places, but let’s be careful to not understate the risks of pollution. The paper states that above 35μg/m^3 of PM2.5 pollution, the protective benefits of exercise were “non-significant” against the increased risk of cancer, and they stopped measuring at 50μg/m^3. It’s reasonable to assume that above 50, it’s a net negative to exercise outdoors.

There are lots of places in the world that exceed 35μg/m^3 PM2.5, and quite a few that exceed 50μg/m^3 PM2.5 regularly - the entire SF Bay Area is over 35 right now. Los Angeles and San Diego are both above 50 right now, as are huge swaths of Eastern Europe, Africa, and Asia... it’s a bit more than just a few handful of cities. Exercising near wildfires can be quite unhealthy too. There are places in the world where exercising outdoors is harmful to your health, but most of that is self-regulating.

The other thing to note from the paper is that even the range of 0 to 10 μg/m^3 of PM2.5 causes a 30% decrease in the benefits of exercise. That’s a pretty big reduction of benefits from exercise for the EPA’s “Good” category of air. It’s still a net positive, so you should still exercise, but just a little pollution has pretty big measurable negative effects.

Active commuting is great, you get exercise, and help reduce pollution at the same time. Even if exercise in polluted areas is beneficial, we also definitely need to keep raising awareness and improving air quality, for the time spent not exercising, for people with athsma and heart disease, for the people who can’t and/or don’t exercise. We should worry about it a little, while we exercise. ;)