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Study: Air Pollution Increases Cardiovascular Disease Risk

Smog over Los Angeles.

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Key Takeaways

  • A new study has linked particle air pollution—pollution caused by tiny solid or liquid compounds hovering in the air—to cardiovascular disease risk.
  • Particle pollution appears to cause arterial inflammation that can eventually induce a stroke or heart attack by prompting leukopoiesis, the production of inflammatory cells in the bone marrow.
  • Experts say that the results of the study could potentially prompt a reevaluation of international safety standards for particulate matter intake.

According to a new study conducted by researchers at Massachusetts General Hospital (MGH), air pollution poses a significant threat to human cardiovascular health.

There are different air pollutants, but MGH's study focused on particulate matter (PM). Particles considered inhalable are conglomerates of solids and liquids. These particles can reach up to 10 microns in diameter—a seventh of the diameter of a human hair. Their lethality increases as their size decreases, which makes evasion of the body's respiratory defenses possible.

Particles 2.5 microns or fewer in diameter (PM2.5) have “the ability to not only be inhalable but also be able to cross the alveolar-capillary membrane"—also known as the blood-lung barrier—“to the circulation and impart their detrimental effects on various organs,” co-first study author Shady Abohashem, MD, research fellow in the department of cardiology at MGH, tells Verywell. 

The researchers followed 503 MGH patients who did not have a history of cancer or cardiovascular disease at baseline for a median of 4.1 years.

In 2013, the World Health Organization determined that PM2.5 was a carcinogen. In the new study, the researchers linked PM2.5 inhalation to risk for a “major adverse cardiovascular event” (MACE).

By the end of the study, 40 of the participants (8%) had experienced a MACE such as a stroke or heart attack. Significantly, according to an analysis of data collected from the Environmental Protection Agency-affiliated air quality monitor closest to their respective residential addresses, those 40 participants had a comparatively high PM2.5 intake. The January study was published in the European Heart Journal

The association remained even after the results were adjusted for other risk factors like healthcare access, socioeconomic status, malignancy history, and “other key confounders."

“Importantly, most of the subjects studied in this population had air pollution exposure well below the unhealthy thresholds established by the World Health Organization, suggesting that no level of air pollution can truly be considered safe,” Abohashem says.

What This Means For You

If you are at an increased risk for cardiovascular disease, making lifestyle changes may reduce your chances of having a heart attack or stroke. You should also limit your exposure to air pollution as much as possible. Consider staying indoors on high pollution days and cleaning indoor air with filters.

How PM2.5 Inhalation Causes Cardiovascular Damage

The researchers identified the source of the link by reviewing earlier PET and CT scans. They found that the participants who had a higher PM2.5 intake produced more inflammatory bone marrow cells, including monocytes, in a process known as leukopoiesis.

Shady Abohashem, MD

These findings implicate air pollution exposure as an under-recognized risk factor for cardiovascular disease.

— Shady Abohashem, MD

Once the cells had passed into the bloodstream, they migrated to neighboring tissues and organs, including the arteries. Once in the arteries, they induced inflammation—a confirmed MACE risk factor. 

“The data helps to build a plausible biological pathway that describes circulatory system component damage that can lead to macro-events of health significance,” Edward Avol, MS, division chief of environmental health at the University of Southern California’s Keck School of Medicine, tells Verywell. Avol was not involved in the study. 

"These findings implicate air pollution exposure as an under-recognized risk factor for cardiovascular disease and suggest therapeutic targets beyond strategies to reduce air pollution to lessen the cardiovascular impact of air pollution exposure,” Abohashem says.

These therapies may include the use of anti-inflammatory drugs and the adoption of lifestyle modifications to reduce leukopoietic activity and the arterial inflammation that results. Abohashem also says that people who are at risk for cardiovascular disease should strive to “minimize their exposure to air [pollution] as much as possible.” 

Will Environmental Regulations Change? 

In 2016, the WHO estimated that outdoor air pollution causes 4.2 million premature deaths each year and that indoor air pollution causes 3.8 million premature deaths each year. Most of these deaths occur in low- and middle-income regions such as Southeast Asia and the Western Pacific.

The results of the study are evidence of the harmful effects of exposure to even mild air pollution. Avol says that by positively correlating PM2.5 intake and cardiovascular disease risk, the study “will strengthen the case that air pollution is a human health hazard and needs to be reduced as quickly as possible."

The research findings may prompt regulatory bodies such as the WHO and the Environmental Protection Agency (EPA) to tighten restrictions on industrial emissions or lower the “unhealthy” threshold even further. 

“My personal opinion is that this study will put increased pressure on the need to strengthen the various regulatory standards that are in effect,” Avol says. 

Abohashem is less optimistic. Unto themselves, he says that “these findings do not confirm that the current WHO threshold [of 10µg/m3 per day, which 91% of the world’s population already exceeds] needs modification."

Still, Abohashem allows that the findings do indicate that “our understanding of the health impacts of exposure to fine particulate matter merits ongoing evaluation.” 

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Article Sources
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  1. United States Environmental Protection Agency. Particulate matter (PM) basics. Updated October 1, 2020.

  2. United States Environmental Protection Agency. What are the air quality standards for PM? Updated October 11, 2019.

  3. World Health Organization (WHO). Ambient (outdoor) air pollution. Updated May 2, 2018.

  4. Abohashem S, Osborne M, Dar T, et al. A leucopoietic-arterial axis underlying the link between ambient air pollution and cardiovascular disease in humans. Euro Heart J. January 2021:1-12. doi:10.1093/eurheartj/ehaa982