Researchers in the United Kingdom explored the benefits of walking in people over 60 and compared the impact on their health when walking along contaminated urban streets versus in the open spaces of a park.
Perhaps not surprisingly, people who walk in the park did better. The surprise was that the benefits of walking were insignificant, in terms of increasing heart and respiratory health, when walking through polluted streets.
"When you walk, your airways open … and your blood vessels dilate or open … and these effects can last a few days.When you do this in a contaminated place, these effects are much smaller, so you've lost the benefits of exercise, "said Dr. Fan Chung, professor of respiratory medicine at Imperial College London, who led the study.
"When you exercise in polluted areas, breathe more and get more particles and gases that reach your lungs," he said.
Pollution versus park
Chung's team set out to discover the effects of pollution in people with heart and lung diseases, most of whom are over 60 years old, he said.
For a fair comparison, a healthy control group was included, but for surprise of the researchers, they saw a significant impact of pollution on everyone.
The team recruited 119 adults older than 60 years and divided them into three groups, depending on whether they were healthy or had heart disease or chronic obstructive pulmonary disease, known as COPD.  Participants were randomly assigned to walk for two hours on Oxford Street in London, a major commercial and highway district in the city, or in the open spaces of the 350-acre Hyde Park, just one mile away. A few weeks later, they walked in the other place.
Traffic along Oxford Street is restricted to allow mainly buses and taxis, which usually run on diesel fuel. In general, London violated the air pollution limits for 2017 only five days of the new year.
For all participants, walking in Hyde Park led to improvements in lung capacity and reduced function and stiffness of the arteries, which would otherwise be a risk factor for cardiovascular disease, up to 26 hours later.
However, when people walked down Oxford Street, the researchers found a smaller increase in lung capacity and an increase in arterial stiffness, which could be attributed to exposure to soot from black carbon and ultrafine particles of gas diesel exhaust.
"In a contaminated place, the (positive) effects are much smaller," Chung said.
People with COPD had the worst case at Oxford Street, with narrowing of their airways and stiffening of their arteries. They also reported more coughing, difficulty breathing, sputum and wheezing.
The team emphasized that some of the benefits of walking in the park could be affected by a more pleasant environment and less stress, but they believe that this does not explain the significant difference they saw.
"If people can not find a green place or a park to exercise, I think they should probably exercise indoors," Chung said.
Walking or not walking
"We're not talking about very high levels of pollution that you see in India or China, we're talking about pollution you get on a normal day walking down the main street," Chung said. . "At that level, we are seeing effects that deny the benefits of walking."
Considers that it is more important that people with heart and lung diseases avoid these areas and adds that despite being conducted in London, the study has global relevance.
"This would apply to European cities and cities in North America where pollution levels are more similar, "Chung said.
Asian pollution is one or two orders of magnitude greater, and studies similar to that level of pollution should be conducted, he said.
Research conducted by teams at the University of Cambridge Activity and Diet Research Center found that the benefits of walking and cycling are greater than the negative effects of air pollution, the opposite of this new study  "Our model indicates that in London, the health benefits of active travel always outweigh the risk of contamination," said lead author of the Marko Tainio research when it was published in 2016. "Even in Delhi, one of the world's most polluted cities ", with pollution levels 10 times higher than in London, people would need to spend more than five hours per week before pollution risks outweigh the health benefits."
In response to new findings, Tainio said, "It is also important to note that this study examined the short-term impacts. … These f The findings should be confirmed by long-term empirical studies that examine compensations over months and years. In addition, Professor Chung and his colleagues noted that the health benefits of walking were lessened, not completely, among healthy participants.
"The authors suggest that people avoid walking on crowded streets and walking in parks or green spaces, and we agree that this is good advice for the recreational walk for people who can make that choice," he added. "But for people who travel daily or shop, even in a city as polluted as London, we still encourage people to walk and ride a bike."
"This document highlights the health risks of walking on polluted roads for people over 60 with pre-existing medical conditions," said Ian Colbeck, professor of environmental sciences at the University of Essex. "However, we know from Another investigation that for the vast majority of the population, the benefits of any physical activity far outweigh any damage caused by air pollution, except for the most extreme concentrations of air pollution. It is important that people continue to exercise. "
Professor Stephen Holgate, Special Advisor on Air Quality at the Royal College of Physicians in the United Kingdom, believes that" we can fully rely on this (new) study that pollution is the factor responsible for changes in function pulmonary. "
Holgate, who was not involved in the new research, added that the sample sizes were small but that" the study deliberately selected COPD and ischemic heart disease in at-risk patients, and … in general, the findings increase the evidence of the importance of the effects of pollutants on vulnerable groups and have implications for the general pollution of vehicles (diesel, gasoline, brakes and tires) as sources of pollutants. "
Tainio stressed that exasperating people to exercise could, in turn, reduce pollution levels."
" However, it is important to remember the role that walking and cycling can play to help reduce air pollution and noise by eliminating motorized transport on the streets. "