So a team of London-based researchers led by Imperial College London set out to investigate the relation between exposure to both air and noise pollution from road traffic during pregnancy and two birth weight outcomes - low birth weight (less than 2500 g) and being born small for gestational age.
Previous BHF research has shown that breathing in high amounts of polluted air is linked to an increased risk of heart attack and stroke.
But after walking on Oxford Street there were only minor improvements in lung capacity, while the measures of arterial stiffness actually got worse which the study associated with "greater exposure to black carbon soot and ultrafine particles from diesel exhaust".
"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", said Simon Gillespie, chief executive at the BHF.
Air pollution from road traffic is having a detrimental impact upon babies' health in London, before they are born, finds a study published by The BMJ today. Researchers said the findings apply to other cities across the United Kingdom and Europe and are calling for policies to improve air quality in urban areas.
The British Heart Foundation says the cardiovascular benefits of a brisk walk along Oxford Street are completely negated by exposure to air pollution for the over 60s.
Commenting on the results, Fan Chung, Professor of Respiratory Medicine and Head of Experimental Studies Medicine at the National Heart & Lung Institute at Imperial College London and senior author of the study, 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".
Blood flow also increased after exercise, with decreases in blood pressure and an increase in heart rate. Healthy volunteers experienced a maximum reduction in arterial stiffness of just 4.6 per cent; COPD patients saw a 16 per cent reduction; and those with heart disease saw an 8.6 per cent reduction. "Our research suggests that we might advise older adults to walk in green spaces, away from built-up areas and pollution from traffic", he added.
Exercising on polluted city streets does more harm than good, research suggests. It is worth noting that stress could account for some of the physiological differences seen between the two settings.
"Combined with evidence from other recent studies, our findings underscore that we can not really tolerate the levels of air pollution that we now find on our busy streets", said Fan Chung, professor at Imperial College in the UK.
"This adds to the growing body of evidence showing the negative cardiovascular and respiratory impacts of even a short, two-hour exposure to motor traffic pollution", said Junfeng Zhang, professor at Duke University in the US. "That should allow everyone to be able to enjoy the health benefits of physical activity in any urban environment".