Sooty air makes walking outside trigger worse COPD cough, study finds
Researchers suggest avoiding busy roads, cite need to reduce air pollution
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When levels of black carbon, or soot, in the air are high, walking outside can worsen cough and increase mucus production in people with chronic obstructive pulmonary disease (COPD), a new study shows.
The researchers note that their findings do not change existing recommendations that people with COPD should try to walk and be physically active whenever possible. However, the data suggest that COPD patients may benefit from limiting physical activity in areas with high levels of soot in the air.
High soot levels are often found in heavily trafficked areas where there’s a lot of car emissions, the researchers noted.
“Our findings support the recommendation to walk for people with COPD, provided that busy roads are avoided where black carbon concentrations are high,” Judith Garcia Aymerich, PhD, the study’s senior author at the Barcelona Institute for Global Health, said in a press release detailing the results the researchers found. Key among them was that a longer walking duration on days with high soot concentrations was associated with increased cough and a greater production of sputum, a mixture of mucus and saliva, among people with COPD.
“It is important to provide accessible spaces for safe walking, as well as to reduce black carbon emissions, a ‘super pollutant’ that is harmful both to respiratory health and the climate,” Aymerich said.
The study, “Effects of the interaction between walking activity and air pollution on daily respiratory symptoms in people with COPD,” was published in the journal Thorax.
It’s well-established that physical activity has many health benefits for people with COPD. As such, “regular physical activity is widely recommended as part of their clinical management, most often in the form of walking activity,” the researchers wrote.
Investigating if air pollution counteracts walking benefits
But when people are walking outside, they may be exposed to more air pollution, which can damage the lungs. Theoretically, the negative impacts of air pollution might counteract the benefits of walking, but there isn’t much data on this issue for people with COPD.
To learn more, a team led by institute scientists conducted a multicenter study in which 105 people with COPD from a region in Spain were monitored for two weeklong periods. In each monitoring period, the participants wore activity monitors to track their walking activity.
The participants also completed daily diaries measuring the severity of several COPD symptoms, namely cough, wheezing, shortness of breath, and expectoration (coughing up mucus or phlegm).
The researchers then cross-referenced the walking and symptom data against data on pollution levels in the area where the participants lived. Specifically, the team looked at three types of air pollution: fine particulate matter (PM2.5), soot, and nitrogen dioxide (NO2).
PM2.5 refers to particles less than 2.5 micrometers in diameter that consist of smoke, aerosols, soot, mold spores, dander, and the like. Soot is a key component of PM2.5 generated by incomplete burning of fossil fuels and wildfires. NO2 is another pollutant made when fossil fuels are burned.
Using statistical models, the researchers looked for significant associations between walking, pollution levels, and COPD symptom severity.
Findings still support walking activity for COPD patients
The results showed that patients who walked for longer on days with high amounts of soot in the air tended to report worse cough and expectoration.
These findings align with previous research suggesting that COPD symptoms tend to worsen when patients walk in areas with heavy traffic, given that soot is produced largely by cars.
These data “support walking activity recommendations for people with COPD, while avoiding high-traffic streets where [black carbon] concentrations are elevated,” the researchers wrote. “Our findings underscore the importance of providing accessible, low-traffic spaces to walk safely.”
For PM2.5 and NO2, there was no significant association between pollution exposure, walking duration, and COPD symptom severity. The researchers noted several potential explanations for these negative findings.
During the study, PM2.5 and NO2 levels were generally low, and below those considered potentially damaging, so it’s possible there just wasn’t enough of these pollutants to have a detectable effect. Another possible explanation is that COPD patients may adjust their behaviors — for example, by using an inhaler more often — on days with more pollution.
Our findings underscore the importance of providing accessible, low-traffic spaces to walk safely.
It’s also plausible that beneficial effects from walking might counteract negative impacts from these pollutants, while soot may have a more potent negative effect on lung health for COPD patients.
“These findings may be explained by the fact that black carbon particles tend to be smaller and can penetrate more deeply into the lungs,” Garcia Aymerich said. “In addition, they often carry compounds that increase their toxicity and their impact on respiratory health.”
Overall, the researchers stressed that their study does not contradict the wealth of prior research showing that walking has long-term health benefits for people with COPD. Instead, these findings simply offer guidance for COPD patients to avoid walking in high-traffic or otherwise polluted areas, the team noted.
Additionally, from a public health perspective, the findings underscore the societal need to limit air pollution so as to minimize its negative health consequences, especially for people with underlying conditions like COPD, the researchers noted.
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