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. The researchers found that levels of pollution - including fine particulate matter, black carbon and nitrogen dioxide - were significantly higher on Oxford Street compared to the park. Average day and night-time road traffic noise levels were also estimated.
Fumes from vehicles in London is linked with a rise of up to six per cent in the odds of a low birth weight and a rise of up to three per cent in the risk of being small for the baby's gestational age, Imperial College London found.
"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", said senior author Fan Chung, "Our research suggests that we might advise older adults to walk in green spaces, away from built-up areas and pollution from traffic".
The project was also supported by the UK Natural Environment Research Council, the Medical Research Council, the Economic and Social Research Council, the Department of Environment, Food and Rural Affairs, and the Department of Health.
The findings show that short-term exposure to traffic exhaust on a busy street can cancel out the positive effects a two-hour stroll would otherwise have on older adults' heart and lungs.
Led by researchers from Duke University, the research is the first large-scale analysis of the effects of airborne traffic-related pollution on both vascular and coronary disease.
All the participants, recruited through London's Royal Brompton Hospital, were either healthy or had a stable lung condition or non-progressing heart disease.
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For the test, 119 healthy volunteers walked for two hours in Hyde Park and a busy part of Oxford Street.
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.
Air pollution levels were monitored before and during their walk, and each participant's lung capacity and arterial stiffness was measured before and after. In contrast, volunteers who walked on Oxford Street had a "worrying increase" in artery stiffness following exercise.
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.
They also found volunteers taking heart drugs such as statins were less affected by the air pollution, suggesting the drugs might protect against the damage.
Other studies have also found associations between traffic-related exposure and atherosclerosis, a hardening and narrowing of the arteries, which can contribute to the risk of heart attack and stroke, as well as type 2 diabetes and inflammation.