ls Running Outside Toxic?

From the WebMD Archives

By Tom DiChiara

If you're like me, the prospect of running outside on a wooded trail with the wind in your face is considerably more appealing than the idea of chugging away on a treadmill, where the air is stagnant and the scenery is either an episode of Friends you've seen 27 times or your own sweaty reflection in the gym mirror. Even so, many people opt for the treadmill -- or simply skip running altogether -- because they're afraid that exercising outdoors will expose them to air pollutants that can cause lung problems (at the very least) or take years off their life (at the very worst). Are these fears founded, or are they a load of hot air?

The Rumor: Running outside exposes you to air pollution that can be hazardous to your health

There's no denying that breathing in carbon-monoxide-laden air on a regular basis is a superb way to develop inflamed lungs, exacerbate asthma and increase the risk of heart attack, stroke, chronic obstructive pulmonary disease, cancer and (by extension) death. Conventional wisdom holds that the potential for these health problems only increases with outdoor exercise, and as Mayo Clinic's Dr. Edward R. Laskowski points out, there's a physiological reason for that. During periods of aerobic activity, says Laskowski, people inhale more air than they do when they're at rest, breathe it more deeply into their lungs and gulp it mostly through their mouths -- bypassing the nasal passages, which normally filter out the dangerous pollution particulates that cars, trucks and buses spew into the atmosphere.

The Verdict: If you're smart about when and where you exercise, running outside is fine and even counteracts the negative effects of air pollution

While Laskowski makes a pretty compelling argument for why you shouldn’t run outside, he admits that it's not the whole story. "What's not clear with air pollution and exercise is how much exposure is a danger, or how long you have to be exposed," he writes. "Because exercise has clear health benefits, don't give up on exercise entirely, unless your doctor has instructed you to."


The "clear health benefits" of running include fighting oxidative stress (a reduction in the body's ability to ward off toxins) and combatting inflammation of the lungs -- which happen to be two of air pollution's biggest adverse effects on the human body. So does that mean that the net benefits of running in polluted conditions outweigh the risks? Conveniently, a 2012 study conducted by researchers in Sao Paulo, Brazil, and published in Medicine & Science in Sports & Exercise posited that very question -- with the aim being to discern "the effects of long-term aerobic exercise on the pulmonary response to DEP [diesel exhaust particles]."

To do so, they monitored four separate groups of lab mice: a sedentary group that did nothing, an exercise group that trained five times a week, a pollution group that was exposed to diesel exhaust particles but didn't exercise and an exercise/pollution group that trained five times a weekand inhaled DEP. Five weeks later, the researchers performed a battery of tests and found that the levels of oxidative stress had skyrocketed in the sedentary mice exposed to DEP, but hadn't really changed at all for the other three groups -- including the aerobically active group that had been subjected to pollutants. The study's conclusion: "Taken together, our results indicate that the decreased inflammatory status achieved by chronic aerobic exercise has a protective effect on DEP-exposed mice, decreasing the pro-inflammatory effects of chronic exposure to air pollution." In short, running protected the mice from the damaging effects of pollution.

Of course, just because this was the case for a few groups of mice doesn't mean it holds true for humans -- but it is encouraging. Also encouraging is the consensus among doctors that runners should most definitely not give up their outdoor routines.

"The bottom line is that running and cycling are healthy and, over all, good for the heart," Dr. David Newby, a cardiology professor at the University of Edinburgh, emphasized in a New York Times article on the risks of pollution for athletes who exercise outdoors.

Dr. Laskowski concurs, advising runners to "focus on ways to minimize the risks of the air pollution-and-exercise combination." These include monitoring pollution levels, timing your outdoor workouts to avoid running when air quality is at its poorest, steering clear of high-pollution areas and occasionally exercising indoors -- just in case you want to catch up on Friends reruns.


To get the most from your outdoor runs, try these tips:

1. Choose your route wisely. If possible, find a running path in your area that is far away from heavily trafficked roads, where carbon monoxide levels can be through the roof. Wooded trails are ideal, since trees filter out air pollution.

2. Time it right. Avoid running outside when pollution levels are highest, which tends to be in the afternoon. Early morning and at night are optimal.

3. Check your local air-quality forecast before heading out. provides up-to-date readings of the Air Quality Index (AQI) by ZIP code, with ratings that range from "hazardous" to "unsafe for certain groups" to "good." Those with heart or respiratory conditions should be extra careful about running on days where the AQI falls on the low end of the spectrum -- and everybody should probably take a rain check on exercising outdoors when the index reads "hazardous."

WebMD Feature from Turner Broadcasting System
© Turner Broadcasting System, Inc.


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