A comprehensive longitudinal study has shown a clear link between long-term exposure to air pollution and an increased risk of developing blood clots in deep veins, known as venous thromboembolism.
The study, which followed over 6,000 U.S. adults across major cities, revealed that exposure to particulate matter, oxides of nitrogen, and nitrogen dioxide significantly heightened the risk, with those in the highest quartile of exposure facing the most severe risks.
Air Pollution and Blood Clot Risks
Exposure to long-term air pollution has been linked to a higher risk of developing blood clots in deep veins, which can block blood flow and cause severe complications, including death if left untreated.
This connection was uncovered in a large, NIH-funded longitudinal study involving 6,651 U.S. adults tracked from 2000 to 2018. Participants lived in or near six major metropolitan areas: New York, Baltimore, Chicago, Los Angeles, Minneapolis, and Winston-Salem, North Carolina.
Over the course of the study, 248 participants (3.7% of the sample) developed deep vein blood clots requiring hospital treatment. The risk of developing these clots increased by 39% to more than double, depending on long-term exposure to three specific types of air pollutants.
Blood clots in deep veins, collectively known as venous thromboembolism (VTE), include deep vein thrombosis, which occurs when a blood clot forms in a deep vein of the legs, arms, or an internal organ, and pulmonary embolism, which occurs when a blood clot breaks off from a deep vein and travels to the lungs.
Pollution Types and Associated Risks
Exposure to air pollution, which can set the stage for inflammation and contribute to blood clotting, has long been associated with cardiovascular and respiratory diseases. While previous research has also suggested a link to VTE, this is the largest, most comprehensive U.S. study to report that association with three different types of air pollutants.
This included exposure to tiny air pollution particles equal to or less than 2.5 micrometers, which can be inhaled from a variety of sources, including smoke from coal-burning power plants, forest fires, and motor vehicle exhaust. Participants with greater overall exposure to this type of air pollution had a 39% increased associated risk for VTE compared to people exposed to lower levels. People with increased exposure to oxides of nitrogen and nitrogen dioxide, pollutants most often found from vehicle exhaust, had a respective 121% to 174% increased risk.
To reach these findings, the researchers analyzed the relationship between patients hospitalized for VTE and levels of air pollution collected through extensive biweekly community-level monitoring — including samples taken from the homes of participants. They then compared those with the highest exposure levels — the top 75% — to those with the lowest exposure — the bottom 25%. They also conducted multiple analyses to control for variables associated with VTE, such as age, exposure to tobacco, and underlying respiratory and other health conditions.
VTE affects up to 900,000 Americans each year. Many cases occur after surgery, but other factors, including age, long periods of inactivity, heart disease, pregnancy, and genetics, can increase risks.
Reference: “Air pollution is associated with increased risk of venous thromboembolism: The Multi-Ethnic Study of Atherosclerosis” by Pamela L Lutsey, Jeffrey R Misialek, Michael T Young, Jesse David Berman, Claire Leiser, Zachary C Pope, Mary Cushman, Aaron R. Folsom and Joel D Kaufman, 12 December 2024, Blood.
DOI: 10.1182/blood.2024026399
The research, which is part of the Multi-Ethnic Study of Atherosclerosis (MESA), was funded by contracts and grants from NIH’s National Heart, Lung, and Blood Institute and National Center for Advancing Translational Sciences, and the Environmental Protection Agency.
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