A new study has found that living near a busy road is associated with peripheral artery disease and high blood pressure in those already at high risk for heart disease, adding to the growing body of research that highlights the dangers of traffic-related air pollution.
A separate study published in The BMJ suggested that pregnant mothers exposed to higher levels of air pollution are more likely to have a baby born at lower birth weights.
Professor Fan Chung, from Imperial College London, who led the research reported in The Lancet journal, 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".
"Babies born with low birth weight or who are small for their gestational age, are at increased risk of dying within their first month, as well as diseases in later life, such as cardiovascular disease".
Although traffic-related air pollution is common worldwide and know to be the source of many health problems, little is known about its impact on vascular health, particularly among people with cardiovascular disease.
The project was again led by researchers from Imperial College London alongside Duke University.
All the participants, recruited through London's Royal Brompton Hospital, were either healthy or had a stable lung condition or non-progressing heart disease.
Participants spent two hours walking along traffic-heavy Oxford Street, which is one the most polluted spots in the United Kingdom, or in Hyde Park.
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The team took physical measurements from the participants before and after the walks and collected data on pollution levels to measure participants' exposure.
But for those in the Oxford Street group there was only a tiny increase in lung capacity, and arterial stiffness got 7 per cent worse.
Analysis revealed that participants benefitted from walking in the park, with lung capacity improving within the first hour and a significant lasting increase for more than 24 hours in many cases.
Blood flow and heart rate also increased after a walk in the park, blood pressure decreased, and arteries became less stiff.
The researchers found levels of pollution - including fine particulate matter, black carbon and nitrogen dioxide - were significantly higher on Oxford Street compared to Hyde Park. "We suggest that, where possible, older adults walk in parks or other green spaces away from busy roads".
"Combined with evidence from other recent studies, our findings underscore that we can't really tolerate the levels of air pollution that we now find on our busy streets", said Fan Chung, professor of respiratory medicine and head of experimental studies medicine at Imperial College's National Heart and Lung Institute.
London Mayor Sadiq Khan claims he is taking "tough measures" to combat air pollution in the capital, such as writing to BMW, Mercedes-Benz and Volkswagen asking them to contribute to the fund set up to tackle the capital's air pollution crisis.
The study was funded by the British Heart Foundation.