Long-term air pollution exposure may worsen the risk of dangerous blood clots in deep veins

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Chronic exposure to common air pollutants may lead to a significantly higher risk of blood clots forming in the veins deep in your body, according to a long-term, observational study that followed more than 6,600 adults across six major U.S. cities.

Those in areas with the highest amount of exposure to outside air pollution—such as motor vehicle exhaust or smoke from forest fires and coal-fired power plants—face the most severe risk of developing venous thromboembolism (VTE), the study shows.  

VTE is estimated to affect up to 900,000 Americans, according to the CDC. Left untreated, these blood clots in deeper veins of the body, including the lungs and leg or arm muscles, can block blood flow and cause serious complications, even death.

While earlier studies indicate a connection between air pollution and venous thromboembolism, this is the most comprehensive, in-depth study in the U.S. to investigate VTE with three types of air pollutants, the researchers say. 

The study adds to mounting evidence that any level of air pollution, which has long been associated with atherosclerotic cardiovascular (ASCVD) and respiratory diseases, is bad for your health, even during pregnancy and early childhood.

“Importantly, air pollution is ubiquitous, so even modest associations can result in a large number of [health] events,” said Dr. Pamela Lutsey, a professor of epidemiology and community health at the University of Minnesota. “What is striking is that these pollutants are very common in the air most of us breathe, and they may be increasing our risk without us realizing it.”

“Even when we looked at people with no evidence of lung disease or smoking, we still saw an association between air pollution and VTE risk.”

Results of the study, published Thursday [Dec. 12, 2024) in the American Society of Hematology’s Blood Journal, show:

Notably, 348 study participants (3.7%) developed blood clots in deep veins that required hospital care, the researchers say.

The findings suggest that air pollution is independently associated with VTE, and not just increasing VTE risk through its role in respiratory disease, Lutsey says. Air pollution may  increase inflammation in the body, she says, and also increase levels of clotting (coagulation) factors in the blood.

“Often when I think about air pollution, I think about a very small increased risk,” Lutsey said. “The strength of associations was stronger than I had honestly expected.”

Nearly twofold risk of developing VTE with highest PM2.5 exposure

VTE is an umbrella term for blood clots that develop in the deeper veins of your body. It consists of:

Chronic thromboembolic pulmonary hypertension, among other complications, may also occur after a PE with a large clot. It stops blood from reaching the lungs and can be fatal.

This latest research is part of the Multi-Ethnic Study of Atherosclerosis (MESA), which recruited participants in 2000-2002. They ranged in age from 45 to 84 years old and came from four groups: white, Black, Hispanic, and of Chinese ancestry. Half were female. All lived in or near New York, Baltimore, Chicago, Los Angeles, Minneapolis, and Winston-Salem, North Carolina.

Throughout the study, researchers updated air pollution metrics in each community every two weeks. They also followed participants, assessing their exposures, over an average of nearly 17 years between 2000 and 2018.

The researchers then compared those with the highest exposure to air pollutants—the top 75%—to those with the lowest—the bottom 25%. They found people in the top percentile had:

Among other limitations, the results of the study may not be transferable to the entire U.S. because it included only six communities, although they were diverse, the researchers say. Also, they identified VTE incidents using hospital discharge codes, misclassifications may have occurred and outpatient cases missed. 

Reducing air pollution worldwide would improve public health, the researchers say.

“This study supports the case for global efforts of pollution reduction to curtail pollution-related adverse health outcomes, which we demonstrate includes risk of VTE.”

Reference

Lutsey PL, Misialek JR, Young MT, et al. Air pollution is associated with increased risk of venous thromboembolism: The multi-ethnic study of Atherosclerosis. Blood Journal. Published online December 12, 2024. doi:10.1182/blood.2024026399