A walk is always healthy — or is it? A new study suggests that walking in a polluted environment can strip away the health benefits of exercise.
"Be active" appears to be the motto that many studies promote nowadays. Exercise has been shown to boost memory, promote gut health, and protect against heart disease, to name a few benefits recently uncovered by researchers.
Still, the effort it takes to get up and go about your physical activity routine may all come to nothing if you live in a big city and find yourself habitually exposed to exhaust fumes and other air pollution factors, a new study suggests.
Researchers from Imperial College London in the United Kingdom and Duke University in Durham, NC, set out to study the effects of pollution on physically active adults aged 60 years and older. Their investigation showed that even a short-term exposure to polluted air can cancel the hard-earned benefits of exercise.
This was also the first time that researchers had looked at the effects of pollution on healthy older adults, as well as on individuals diagnosed with chronic obstructive pulmonary disease (COPD) or coronary heart disease.
According to study co-author Prof. Junfeng Zhang, of Duke University, the new study "adds to the growing body of evidence showing the negative cardiovascular and respiratory impacts of even a short, 2-hour exposure to motor traffic pollution." The results, he adds, "[Highlight] the need for stricter air quality limits and better traffic-control measures in our cities."
Prof. Zhang and colleagues recently published their findings in The Lancet.
A walk in the park for heart and lung health
For the purpose of the study, the researchers recruited 119 participants over 60 years of age, of whom 40 were healthy, 40 had a pre-existing diagnosis of COPD, and 39 had ischemic heart disease.
The participants were asked to take a 2-hour walk at midday either in a quiet part of Hyde Park in London, U.K., or along the busy Oxford Street — one of the most polluted spots of the British capital.
Both before and after the walk, the participants underwent tests measuring the effects on heart and lung health, taking into account elements such as lung capacity, blood flow and pressure, and arterial stiffness.
The researchers found that — regardless of their initial state of health — the participants who had gone for a walk in Hyde Park experienced a marked improvement of lung capacity within the first hour.
This benefit was prolonged for more than 24 hours in the case of many of the park-going participants.
At the same time, the volunteers who were asked to walk along Oxford Street experienced a limited lung capacity increase to begin with, which was not maintained throughout the hours following the walk.
A walk in Hyde Park was also seen to counteract arterial stiffness, reducing it by over 24 percent in healthy participants and participants with COPD, and by over 19 percent in individuals with heart disease.
Those who walked along the busy London street did not experience significant improvements in this regard, with healthy participants reaching only a 4.6 percent reduction in arterial stiffness.
Participants with COPD experienced a 16 percent reduction, and those with a heart disease diagnosis exhibited a reduction in arterial stiffness of only 8.6 percent.
However, the team did acknowledge some limitations to the study, noting that the stress levels experienced on the busy street of a capital city — produced by exposure to loud noise and lively crowds — might have influenced the results.
They also noticed that the participants taking drugs for cardiovascular symptoms were affected less by exposure to air pollution. In the study paper, the researchers write that "our data suggest that cardioprotective drugs taken by participants with ischemic heart disease are beneficial when walking in polluted areas."
No tolerance for current levels of air pollution
Despite any drawbacks in the study design, the researchers express concern following their findings.
They say that most worryingly, older adults or those diagnosed with chronic heart or lung diseases might have few options when it comes to exercise. In their case, walking may be the most readily available physical activity, so the environment to which they are exposed is extremely important.
"For many people, such as the elderly or those with chronic disease, the only exercise they very often can do is to walk. Our study suggests that we might advise these people to walk in green spaces, away from built-up areas and pollution from traffic. But for those living in inner cities, this may be difficult to do [...]"
Study co-author Prof. Kian Fan Chung, National Heart & Lung Institute, Imperial College London
The researchers call for a "zero tolerance" policy when it comes to high pollution levels, and they suggest that more stringent measures should be taken in this respect.
Prof. Fan Chung says, "Combined with evidence from other recent studies, our findings underscore that we can't really tolerate the levels of air pollution that we currently find on our busy streets."
He adds that he and his colleagues "call for greater access to urban green spaces for people to exercise," following the significant heart and lung health improvements seen in those who spent time walking in the quiet, fresh environment of the London park.