U.S. researchers say urban dwellers exposed to the highest levels of fine particulate air pollution had faster hardening of the arteries, putting them at increased risk of stroke, compared to people in less polluted sections of the same city. The finding adds to a growing body of evidence that residing in polluted urban areas is a risk factor for cardiovascular disease.
Atherosclerosis, or hardening of the arteries, is a leading cause of death around the world. It can cause stroke or death when a blood clot or piece of hardened plaque inside a blocked coronary artery breaks off and travels to the brain, cutting off blood flow.
To investigate the role of air pollution in the development of atherosclerosis, researchers followed a group of almost 5,400 adults in six metropolitan areas. None of the participants was known to have heart disease. They were part of a larger U.S. study called the Multi-Ethnic Study of Atherosclerosis and Air Pollution, or MESA Air.
Between 2000 and 2005, researchers conducted two non-invasive ultrasound examinations on each participant, at intervals of three years, to measure the thickness of the subjects' carotid artery walls. The carotid carries blood to the head, neck and brain. Thickening of an arterial wall is a good indicator of atherosclerosis throughout the body, even in patients with no obvious symptoms of heart disease.
Analyzing the ultrasound results, researchers found a slight, but significant increase in the thickening of carotid artery walls among individuals who resided in high pollution areas compared to those in less polluted urban centers. According to lead researcher Sara Adar, an epidemiologist at the University of Michigan School of Public Health, their findings corroborated earlier studies of the group.
“Based on another study that was done in the same cohort [group] of people, they found that the amount of change that we saw for living in a high-pollution neighborhood versus living in a low pollution neighborhood would correspond to about a two percent increased risk of stroke," said Adar.
Fine particulate air pollution, the kind of black soot belched out by smoke stacks and the tailpipes of buses in many urban areas around the world, is widely believed to cause inflammation and oxidative stress that can contribute to heart disease.
Adar says people already are encouraged to stay indoors on days when pollution is particularly high. But she says doctors should make a point of discussing the hazards of air pollution with their patients:
“So, just as they might ask somebody 'Do you smoke?' or think about if someone is obese, [the question of] how long someone has lived in a highly polluted environment might factor into a physician’s notion of whether or not somebody is at high or low risk for cardiovascular disease or heart disease," she said.
An article linking air pollution to accelerated hardening of the arteries is published in the journal PLoS Medicine.