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Walking on polluted streets cancels some of the activity's positive health effects, study finds

Oxford Street
REUTERS/Peter Nicholls
The researchers note that stress from the increased noise and activity of Oxford Street may have had an effect on the study’s results.

Walking is a highly recommended form of exercise, particularly for older people, but doing it on polluted, traffic-congested streets can cancel out its beneficial effects on the heart and lungs, according to a British-American study published Tuesday in The Lancet.

And it isn’t just individuals with pre-existing heart and lung conditions who experience those negative effects. They also occur among healthy people, the study found.

Pollution likely has similar effects on people of all ages, the study’s authors add.

They call on governments “to impose policies and measures that can reduce traffic pollution so that every individual can enjoy the health benefits of physical activity.”

They also call for more green spaces in urban environments.

Two London walks

For the study, researchers at Imperial College London and Duke University recruited 199 volunteers aged 60 and older. Two-thirds of the volunteers had been diagnosed with either heart disease or chronic obstructive pulmonary disease (COPD), while the others were healthy (no pre-existing heart or lung condition).

The volunteers were asked to take two-hour walks at midday in two London settings: a busy section of Oxford Street (which regularly exceeds international air quality limits) and a relatively quiet, traffic-free area of Hyde Park. Before and after the walks (which averaged 3.1 miles at each setting), the participants underwent various tests that are designed to assess the effects of exercise on heart and lung health. These included measurements of blood pressure, lung capacity, blood flow and stiffness of the arteries.

Noise and air pollution in both of the settings were also measured at the times of the walks. Not surprisingly, the Oxford Street setting had significantly higher levels of both, including greater amounts of black carbon, nitrogen dioxide and fine particulate matter.

Key findings

After analyzing all the data, the researchers found that all the participants benefitted from their stroll in Hyde Park. Specifically, their lung capacity improved within the first hour — and, in many cases, that improvement continued for more than 24 hours. By contrast, lung capacity improved only slightly during the Oxford Street walk — and did not last.

Significant differences in arterial stiffness were also observed. Walking in Hyde Park reduced arterial stiffness by a maximum of more than 24 percent in the healthy and COPD volunteers and by more than 19 percent in the patients with heart disease. But the maximum change resulting from the Oxford Street walk was 16 percent for people with COPD, 8.6 percent for those with heart disease and a meager 4.6 percent for the healthy volunteers.

In the healthy volunteers, the reduction in arterial stiffness resulting from the walk in Hyde Park persisted for up to 26 hours. That benefit disappeared — or even reversed itself — after walking on Oxford Street. 

Interestingly, the study found that the volunteers with heart disease who were being treated with medication were less negatively affected by the pollution.

Limitations and implications

The study has several limitations. It involved, for example, a small number of participants, all of who were from the London area. The results may or may not be applicable to people living elsewhere. The study also had people take only two short walks. It can’t tell us, therefore, what the long-term benefits (or non-benefits) of exercise are in relation to pollution.

The researchers also note that stress from the increased noise and activity of Oxford Street may have had an effect on the study’s results.

Still, the findings point to how difficult it is for many people to personally improve their health when the built environments of our communities do not support — or even undermine — those efforts.

“For many people, such as the elderly or those with chronic disease, the only exercise they very often can do is walk,” said Kian Fan Chung, the study’s senior author and a professor of respiratory medicine at Imperial College London, in a released statement. “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, and there may be a cost associated with it as they have to travel further away from where they live or work.”

“We need to reduce pollution so that everyone can enjoy the benefits of physical activity in any urban environment,” he added.

FMI: You’ll find the study on The Lancet’s website.

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Comments (2)

Or, someone could subsidize a

Or, someone could subsidize a gym membership for those frail elderly, getting them to walk (and do other exercise) off those awful urban streets. Same for the non-frail, non-elderly.

Or, one could ban all automobiles, which is the preferred outcome I perceive in this absurdly small study.

Too small

Offhand, this nonprofessional daily urban walker thinks the study is too limited, and involves too small a sample, to draw conclusions that have real validity. At best, it "suggests," but that's "at best." Overall, I'd say it doesn't prove anything.