Scientists from Imperial College London measured the health boosts that people aged over 60 received from brisk walks in different parts of London.
'When exercising it's best to avoid highly-polluted areas, swapping them for green spaces or even back streets where pollution is lower. "This will ensure you can experience the full benefits of exercise", said chief executive of the British Heart Foundation (BHF) Simon Gillespie, whose organization funded the study.
Physical measurements were taken before and after the walks to show the effects of the exercise on cardiovascular health, including measurements of lung volume exhaled, blood pressure, and the degree to which the blood vessels could expand.
The lecturers point to the improvement of air quality in Berlin during the 2008 Olympics as an example of what can be achieved, but said the challenge is to maintain reductions in pollution in the longer term with measures such as reducing congestion and tackling diesel emissions.
They were unsurprised to find that noise and pollution levels were significantly higher on Oxford Street than in Hyde Park, including higher levels of black carbon, nitrogen dioxide and fine particulate matter (PM2.5) which has a diameter of less than 2.5 micrometers and can enter the lungs and even the bloodstream.
In comparison, when they walked in Hyde Park "all participants, irrespective of their disease status..." By contrast, lung capacity improved only slightly during the Oxford Street walk - and did not last.
To conduct the study, the researchers recruited 119 volunteers over the age of 60 who were either healthy, had stable COPD, or stable ischemic heart disease.
Transient subjection to traffic exhaust in built up locations like New York City's Broadway or Chicago's Michigan Avenue can annul the positive outcomes of a two hour walk which would have benefitted the heart and lungs of these people. Arteries became less stiff in those walking in Hyde Park with a maximum change from baseline of more than 24 per cent in healthy and COPD volunteers, and more than 19 per cent in heart disease patients.
The study added: "These beneficial responses were attenuated after walking on Oxford Street".
In addition, the researchers founsd that for those patients with heart disease, taking medication that improved the cardiovascular system was associated with a stabilising effect, and may prevent them from deteriorating in areas with higher levels of air pollution. The results may or may not be applicable to people living elsewhere.
"Exercise is crucial in reducing the risk of a heart attack or stroke, but it seems risky levels of air pollution could be erasing these benefits in older adults".
Although the team noted that stress could be a contributing factor, with the increase in noise and the number of people on Oxford Street another reason behind the physiological differences observed, the new findings still add to the growing body of evidence on the dangers of urban air pollution.
Still, the findings point to how hard 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.
Professor Fan Chung, who led the research, said, "these findings are important as for many people, such as the elderly or those with chronic disease, very often the only exercise they can do is to walk".
Two studies published by researchers in London this week (5 December) have uncovered health impacts from exposure to air pollution in both unborn babies and the over-60s.
They also suggest older adults walk in green spaces that are away from polluted or high-traffic areas.
"For people living in the inner city it may be hard to find areas where they can go and walk, away from pollution".
"We need to reduce pollution so that everyone can enjoy the benefits of physical activity in any urban environment", he added.