New Kaiser Permanente study quantifies the impact of small particle pollution on cardiovascular diseases
By Sue Rochman
There is strong evidence that persistent exposure to the small particles that make up the all-too-familiar haze of air pollution carries an increased risk of dying from cardiovascular disease, a new meta-analysis from Kaiser Permanente researchers shows.
“The general consensus has been that long-term exposure to air pollution has cardiovascular effects,” said Stacey Alexeeff, PhD, a research scientist and biostatistician at the Kaiser Permanente Northern California Division of Research who led the study. “What we did in this study is figure out which cardiovascular effects we know most about, the effects we have the most evidence to support, and the types of cardiovascular disease we should be most concerned about.”
The paper, published online in the Journal of the American Heart Association, is the first to quantify and compare the effects of long-term exposure — defined as a year or more — to fine particulate matter (PM2.5) pollutants on risk of having a first heart attack or stroke or dying from coronary artery disease or stroke. The meta-analysis of results reported in 69 previous papers found long-term exposure to air containing these fine particles increased the risk of death from coronary heart disease by 23% and from stroke by 24%. Long-term exposure to these air pollutants increased the risk of a first stroke by 13% and a first heart attack by 8%.
“This meta-analysis parses out the impact of air pollution on specific cardiovascular disease outcomes in a way that hasn’t been done before,” said the study’s senior author Stephen Sidney, MD, MPH, a research scientist at the Division of Research. “It reinforces the need to direct policy efforts to improve air quality in order to reduce the societal burden of heart disease, stroke, and the 108,000 deaths in the U.S. each year which are directly attributable to air pollution.”
Long-term air pollution exposure is an important modifiable risk factor for cardiovascular disease that needs to be taken seriously.”
— Stacey Alexeeff, PhD, research scientist
Particle pollution is measured in microns; about 25,000 microns equal an inch. A PM2.5 particle is 2.5 microns or less in size, or about 30 times smaller than the width of a piece of hair. These minute particles are released in exhaust from cars, trucks, and other vehicles; from burning wood, heating oil, and coal; and by factories, power plants, and forest fires.
Scientists have identified the reasons why breathing in these small particles can affect the blood vessels and heart. “The key mechanisms are thought to be oxidative stress and inflammation,” said Alexeeff. Oxidative stress occurs when an imbalance develops inside cells and tissue between the production and elimination of oxygen reactive species, the unstable molecules known as free radicals that can damage a cell’s DNA, RNA, and proteins. The overload of free radicals can cause a type of chronic inflammation that leads plaque to build up in the arteries. If a piece of this plaque breaks off, it can cause a blood clot, resulting in a heart attack or stroke.
The new analysis accentuates the significance of the research showing Black, Latinx, and low socioeconomic neighborhoods are exposed to higher concentrations of small particle air pollution. “This is primarily because these groups are more likely to live in high-traffic areas or in close proximity to factories, power plants, and refineries that release high levels of this type of pollution,” said Sidney, who co-authored a policy statement published recently by the American Heart Association on ways to mitigate the effects of air pollution. “This structural racism must be addressed to reduce risk for cardiovascular disease in these communities.”
Alexeeff said it would be important for future studies to determine which specific particles are the greatest drivers of the increased risk of cardiovascular disease. “These particles come from different sources, and the mix of components in the air varies by regions,” she explained. “It would be important to know not only overall concentrations, but which specific particles cause the most harm.”
When talking about long-term exposure, Alexeeff said, “what we are really talking about is where people live. People can’t just move to a cleaner area. The level of increased risk we found means that long-term air pollution exposure is an important modifiable risk factor for cardiovascular disease that needs to be taken seriously.”
This study was funded by the National Institute of Environmental Health Sciences.
Co-authors include Noelle S. Liao, MPH, Xi Liu, MPH, and Stephen K. Van Den Eeden, PhD, of the Division of Research.
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About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit divisionofresearch.kaiserpermanente.org or follow us @KPDOR.