Air pollution is bad for your health and exercise is good—but what happens when the two mix? 

A recent study by a Duke researcher showed that city air pollution cancelled out the positive effects of exercise on the health of adults older than 60, impacting their heart and lungs. Jim Zhang, professor of global and environmental health and co-author of the study, explained that the idea for the research came from observing how older people who live in cities frequently get their exercise by walking. 

“We would encourage people to do that kind of physical activity, but at the same time we worried about people being exposed to traffic-generated air pollution while walking in busy traffic areas,” he said.  

Published Dec. 5 in the journal "The Lancet," this is the first study to find negative effects of air pollution on both healthy individuals and those with pre-existing conditions like chronic obstructive pulmonary disease and pulmonary disease.

The researchers had 119 volunteers older than 60 walk for two hours in the middle of the day at one of two locations in London—a quiet part of Hyde Park or Oxford Street, the latter of which experiences pollution such as black carbon, nitrogen dioxide and fine particulate matter. The participants' lung capacity, blood pressure, blood flow and arterial stiffness were measured before and after the walk.

The volunteers who walked in Hyde Park experienced improved lung capacity in the first hour, and this benefit lasted for more than 24 hours in many of them. However, those who walked along Oxford Street had less of an improvement in lung capacity and no increase later on. 

In addition, the walk in Hyde Park reduced the healthy and COPD volunteers’ arterial stiffness by more than 24 percent and by more than 19 percent in the participants with heart disease. The walk on Oxford Street resulted in a maximum reduction in arterial stiffness of only 4.6 percent in healthy volunteers, 16 percent in COPD volunteers and 8.6 percent in those with heart disease.  

“With walking being the most important form of exercise that everyone, healthy or those with heart or lung disease, needs to do to keep well, it is important that this is done in a pollution-free area in order to reap the benefits of walking,” Fan Chung, head of experimental studies medicine at the National Heart and Lung Institute at Imperial College in London and a co-author of the study, wrote in an email. 

Chung explained that the study focused on older adults because they are often more susceptible to the negative effects of air pollution than those who are young and healthy. Zhang added that though many people believe that air pollution is only a problem in places like China and India, this research shows that it’s also significant in the United Kingdom. He noted the importance of reducing emissions in urban areas by reducing diesel vehicles in favor of electric-powered ones. 

Due to the improvements in lung and vascular functions among those who walked in the park, the researchers also called for increased access to urban green spaces for exercising. 

“If you cannot completely convert all gasoline and diesel to electric, then you really need to get more green spaces,” Zhang said. 

Chung also noted that cities should provide clean parks for people to exercise or make alternative arrangements to still encourage physical activity. If that's not possible, then walking indoors should be made available.

In the future, Chung wrote that he hopes to study whether similar effects of urban pollution also occur in younger people and when individuals are taking part in forms of more intense exercise. 

“In this case, we will also be dealing with increasing amounts of pollution to which the lungs are exposed to,” he wrote. “Then comes the balance between the benefits of exercise versus the direct effects of increased amounts of pollution that the lungs get exposed to.”