A local runner explores what the recent air-pollution study, led by a UW professor, could mean to people who like to exercise in the urban outdoors.

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You’ve seen us — crowds of runners, cyclists and walkers, bouncing and shifting in place amid idling cars at stoplights. After all, the area’s running trails, bicycle-friendly roads and high walkability scores have helped Greater Seattle ascend to sixth place in the 2016 “Fittest City” ranking by the American College of Sports Medicine.

On any given day, my friends and I are among the people you see using the trails for recreation or transportation.

We’ve discovered firsthand the downside to our city’s popularity and livability: traffic. Seattle now ranks fourth worst among U.S. cities in traffic congestion, according to TomTom Traffic Index. More vehicles, more waiting.

Tips for reducing your risk

Here are some ways you can protect yourself from the effects of pollution, from UW professor and environmental-health specialist Dr. Joel Kaufman:

• Plan your route away from major roadways.

• Check pollution levels at Airnow.gov, which features an Air Quality Index (AQI) and PM2.5 particulate readings by ZIP code.

• Reduce pollution exposure while driving, by checking your cabin air-filter quality frequently. When you turn on the air conditioner, check that the airflow is not set to pull in dirty air from outside.

• Consult your doctor to learn your risks for heart disease. Insurance often covers heart-related blood tests, and the cost of CT heart scans has dropped to around $100 locally.

And with traffic comes pollution, which, according to a recently released University of Washington study, triggers biological processes that lead to heart disease. Should Seattle-area residents training for century bike rides and marathons be concerned?

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Confidentially: I am! Because among my urban running peers, only a small subset — including me — actually has to mind health metrics like cholesterol and coronary calcium scores. But all of us believe, down to our zero-drop insoles, that exercise helps prevent heart disease. Now, evidence shows that outdoor exercise may contribute to it.

The MESA Air study, led by Dr. Joel Kaufman, a UW professor and environmental-health specialist, showed how long-term air-pollution exposure increases coronary calcium deposits. These deposits block the flow of blood, causing heart attacks and strokes.

Researchers used computed tomography (CT) scans and other tests to measure their subjects’ exposure to soot, nitrogen dioxide and oxide, and microscopic particles called PM2.5. Unfortunately, athletes who train outside are at greater risk from these pollutants because they inhale 10 to 20 percent more air than sedentary people.

Dr. Dan Tripps, chief operating officer and director of exercise and science at Potentrx in Seattle, says it is because athletes shift from nasal breathing, which filters some bad air, to breathing through their mouths. While doing so, they are increasing not only their breathing rate, but the volume of air ingested, and the particles that come with it.

What are the study’s implications for outdoor athletes? Kaufman, a bicycle commuter, believes the benefits of exercise outweigh the risks. He cites major improvements in U.S. air-pollution reduction as one reason outdoor exercise is generally safe, although he adds, “Thus far, we haven’t seen any safe level of pollution.”

While fitness apps encourage athletes to fixate on training metrics and dashboards, Tripps encourages people to focus on their “heart metrics” — blood pressure numbers, cholesterol levels, and (for at-risk individuals) coronary calcium scores. Those concerned about air pollution’s impact on their heart can create a personal dashboard, he says, and use those numbers to monitor their health and performance.