Published February 20, 2020

Ozone pollution contributes to smog in Los Angeles.Extensive scientific evidence on the health impacts from exposure to ozone has been used to support the regulation of ozone under the Clean Air Act for nearly half a decade. While the major research focus has been on ozone’s detrimental effects on the lungs, a large 2016 study has suggested ozone exposure may have impacts on the cardiovascular system as well¹.

EPA-funded research has found a potential relationship between long-term exposures to ground level ozone and the changes over time in the health of arteries that feed both the brain (carotid arteries in the neck) and heart (coronary arteries).  

Researchers used results from ultrasound measurements of participants’ carotid arteries and special x-ray tests called computerized tomography (CT) scans of the coronary arteries over time to determine their health. In addition, they estimated long-term exposure to outside ozone concentrations where the participants lived using sophisticated and novel measurement and statistical methods. The average duration of exposure was 6.5 years and for some participants over 10 years. In a paper published in 2019, researchers found a strong correlation between increasing  ozone concentrations and carotid artery injury as measured by thickening of the carotid artery and the build-up of plaque in the artery’s wall. When the walls of carotid arteries thicken, or plaque builds up, the risk for stroke increases. They found an increase in carotid artery thickness of 5.6 micrometers with a 3 parts per billion increase in the mean annual ozone concentration²_.

The study revealed significant physical changes to carotid arteries related to the ozone exposure but not to coronary arteries of the heart.  

“It was surprising because we were not expecting to see a strong association between ozone and vascular findings,” says Joel Kaufman, professor at the University of Washington in Seattle and lead investigator for MESA AIR Next Stage, the name of the research project.    

Further research is needed, he adds, but the study provides a major contribution to filling the gap in knowledge on the effects of elevated ozone over time. 

“The study provides additional evidence to support the biological plausibility that oxidant gases like ozone could be related to cardiovascular and vascular health,” Kaufman says.

“The fact that we saw these changes in the carotid artery [from ozone exposure] instead of the coronary artery suggests that the underlying mechanisms by which ozone might cause cardiovascular disease are different than PM (particulate matter) and oxides of nitrogen,” he says.

1. Am J Respir Crit Care Med. 2016 May 15;193(10):1134-42. doi: 10.1164/rccm.201508-1633OC. Long-Term Ozone Exposure and Mortality in a Large Prospective Study. Turner MC, Jerrett M, Pope CA 3rd, Krewski D, Gapstur SM, Diver WR, Beckerman BS, Marshall JD, Su J, Crouse DL, Burnett RT
2. Wang, M., Sampson, P. D., Sheppard, L. E., Stein, J. H., Vedal, S., & Kaufman, J. D. (2019). Long-Term Exposure to Ambient Ozone and Progression of Subclinical Arterial Disease: The Multi-Ethnic Study of Atherosclerosis and Air Pollution. Environmental Health Perspectives, 127(5), 057001. doi:10.1289/ehp3325