Pollution likely has similar effects on people of all ages, the study's authors add.
Prof Stephen Holgate from Southampton University and special adviser to the Royal College of Physicians on air quality, said: "The observation that air pollution encountered on a high street in London removes any health protection produced by exercise outdoors is yet another demonstration that pollution is eroding the health of ordinary people".
The participants were randomly assigned to walk around either Oxford Street or Hyde Park. 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.
Blood flow increased, blood pressure fell and arteries became 24 per cent less stiff.
Air pollution levels were monitored before and during their walk, and each participant's lung capacity and arterial stiffness was measured before and after.
After analyzing all the data, the researchers found that all the participants benefitted from their stroll in Hyde Park.
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The study found everyone in the park group benefited, with lung capacity improving within an hour and persisting for 24 hours.
This effect was drastically reduced when walking along Oxford Street, however, with a maximum change in arterial stiffness of just 4.6% for healthy volunteers, 16% for those with COPD and 8.6% for heart disease. Many of us might think everything will be fine if we are healthy in other parts of our life, like eating well and exercising regularly. That benefit disappeared - or even reversed itself - after walking on Oxford Street.
The latest study, funded by the British Heart Foundation, is the first to show the negative effects of air pollution on healthy people, people with a chronic lung condition linked with smoking called Chronic Obstructive Pulmonary Disease (COPD), and those with coronary heart disease - which affects the supply of blood to the heart. The study also had people take only two short walks.
On the other hand, those on Oxford Street experienced a smaller increase, and their results did not last for the rest of the day.
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.
"For many people, such as the elderly or those with chronic disease, the only exercise they very often can do is to walk", added Fan Chung, Professor at the Imperial College London.
'For people living in the inner city it may be hard to find areas where they can walk, away from pollution ... we really need to reduce pollution by controlling traffic'. "But for those living in inner cities, this may be hard to do, and there may be a cost associated with it as they have to travel further away from where they live or work".
"We know from other research that for the vast majority of the population the benefits of any physical activity far outweigh any harm caused by air pollution except for the most extreme air pollution concentrations", he said.