Scientists are now cautioning us that the path we walk on is as important as the walk. They report that the health benefits of walking exercise can be reduced, cancelled out, or even reversed, if we walk in traffic-polluted air.
They show that the detrimental effect of air pollution on walking at a normal pace occurs not only in people with respiratory and heart conditions, but also in healthy individuals.
Their study also provides insight into the type of pollutants that are responsible for the association between air pollution and an increase in cardiovascular disease risk and death. The findings are published in the scientific journal The Lancet.
Background
Walking is an important daily activity, and is the most affordable, feasible, dependable, and commonly prescribed way to get the amount of exercise recommended for health and well-being.
The association between human exposure to fine particulate matter air pollution and an increased risk of cardiovascular disease and death is well documented.
The Global Burden of Disease study recently estimated that exposure to fine particulate matter air pollution contributed to 4.2 million deaths in 2015, making it the 5th ranked risk factor for global death. Deaths from cardiovascular disease accounted for most of these deaths attributed to environmental fine particulate matter air pollution.
Heavy city traffic air pollution caused by diesel-powered vehicle emissions and tires and brakes of motorcars comprises of fine particulate matter, ultrafine particles, and noxious gases such as nitrogen dioxide. These individual pollutants and their mixture have been associated with early deaths, and adverse respiratory and cardiovascular events.
Even in healthy individuals, other studies have shown that exposure to diesel exhaust causes immediate and transient increases in arterial stiffness and pulmonary inflammation.
Researchers here aimed to assess the respiratory and cardiovascular effects of a short-term traffic pollution exposure during a 2-hour walk on a busy London street, and compared them with those effects in the same individuals during a similar walk in the Hyde Park.
The study and findings
Forty healthy individuals, 40 participants with chronic obstructive pulmonary disease, and 39 participants with ischemic heart disease, all aged 60 years and older, took part in the study.
Following the walk in the park, all participants, regardless of their health status, showed beneficial increased lung function and decreased arterial stiffness, as measured in pulse wave velocity and augmentation index.
By contrast, these benefits were significantly reduced or reversed after walking along the traffic-polluted street. The adverse effect of air-pollution exposure on vascular function during physical activity is clearly evident.
Specifically, among healthy individuals, there was about 5% decrease in pulse wave velocity from 2-26 hours after the walk in the park. This exercise benefit was reversed 26 hours after the traffic-polluted street walk, with an average 7% increase in pulse wave velocity.
The researchers also find that traffic air pollution causes phospholipid oxidation and oxidative stress. They suggest that these pathways accelerate atherogenesis and increase arterial stiffness.
Implications
The findings of this study are in line with previous studies showing an association between traffic air pollutants and cardiovascular disease and death, and support the view that pollutants from fossil fuel combustion are particularly toxic for individuals with cardiovascular or pulmonary conditions.
Running along or near busy highways or cycling during rush hour have also been shown to cause a reduction in lung function in other studies.
This study suggests that health individuals, as well as those with cardiorespiratory conditions, should minimize walking on streets with high levels of traffic pollution, because this reduces or even reverses the cardiorespiratory benefits of the walking exercise.
