The study found no evidence that exposure to road traffic noise was linked to birth weight but the authors said they "cannot rule out that an association might be observed in a study area with a wider range of noise exposures".
For the research, the team recruited 119 volunteers over the age of 60 who were healthy, had stable COPD, or had stable heart disease. Before and after the walks (which averaged 3.1 miles at each setting), the participants underwent various tests that are created to assess the effects of exercise on heart and lung health.
Previous BHF research has shown that long-term exposure to air pollution leads to inflammation in the blood vessels, including those supplying the heart, and promotes the buildup of fatty plaques in the linings of blood vessels, which can eventually lead to a heart attack or stroke. 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).
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.
An analysis of the data found that increases in traffic-related air pollutants were associated with 2% to 6% increased odds of low birth weight and 1% to 3% increased odds of being small for gestational age. Specifically, their lung capacity improved within the first hour - and, in many cases, that improvement continued for more than 24 hours.
Blood flow and heart rate also increased after a walk in the park, blood pressure decreased, and arteries became less stiff.
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.
Oxford Street walkers who were healthy only had a 4.6 percent drop, coronary heart disease subjects saw 16 percent dip and those with ischemic heart disease only experienced a 8.6 percent reduction.
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Pedestrians walk along London's busy Oxford Street. They also noted that patients with heart disease who took medication to improve their cardiovascular health experienced less severe effects following exposure to the pollution.
Scientists from Imperial College London measured the health boosts that people aged over 60 received from brisk walks in different parts of London.
Air pollution is a serious issue, but there are very few cities in the world where it outweighs the benefits of exercise.
It also isn't clear that pollution was the cause of the physiological differences.
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.
Commenting on the findings, Dr Mireille Toledano, from the School of Public Health at Imperial College London and senior author of the research, said: "Our study has shown that a small but significant proportion of babies born underweight in London are directly attributable to exposure to air pollution, particularly to small particles produced by road traffic". "Our study suggests that we might advise these people to walk in green spaces, away from built-up areas and pollution from traffic".
"For people living in the inner city it may be hard to find areas where they can go and walk, away from pollution. That should allow everyone to be able to enjoy the health benefits of physical activity in any urban environment".
The findings can be found published online in The Lancet.