Particulate Air Pollution, Heart Attacks, and Blood Hyperclotting

A study from Northwestern University’s Feinberg School of Medicine has shown that microscopic air pollution – smaller than one-tenth of the diameter of a human hair — causes hyperclotting of the blood. The study found that lungs inflamed by particulate pollution produce an inflammatory cytokine, interleukin-6, that causes an increased tendency for blood to coagulate or clot. (3) This in turn raises the risk of a fatal heart attack or stroke in people with cardiovascular disease such as coronary artery disease, congestive heart failure or a history of stroke.

Missing Puzzle Piece

It is known from epidemiologic studies that death from, congestive heart failure (1), and ischemic stroke (2), are linked with heavy exposure to particulate matter pollution. The exact mechanism, however, of these deaths was never examined until now.

    “This is a critical missing piece of the puzzle that has eluded scientists for decades,” said Gokhan Mutlu, M.D., lead author of the study and assistant professor of pulmonary and critical care medicine at the Feinberg School, and a physician at Northwestern Memorial Hospital. “Now we know how the inflammation in the lungs caused by air pollutants leads to death from cardiovascular disease.”


Those at risk may be able to help protect themselves by taking low-dose aspirin to keep their blood thin, Dr. Mutlu advised.

The study, published in the Journal of Clinical Investigation issue Oct. 1 2007 issue, used particles of pollution collected by the United States Environmental Protection Agency, mixed into a saline solution and injected the pollution concoction into the lungs of mice. The blood of the mice exposed to the pollution clotted faster than mice not exposed. Researchers saw a 15 times increase in interleukin-6 24 hours after the mice were exposed to the pollution.

Death Risk Increases 30% per 10 Micrograms of Pollution

According to a 2007 report from the American Lung Association, the most “ominous trend” in air pollution is now the increase in particle pollution, principally in the eastern United States. Among the metropolitan areas, Los Angeles has the most year-round particle pollution. Chicago ranks 11; New York, 17 and Washington D.C., 20. All received an “F” or failing grade for their pollution , which was in excess of the EPA annual average limit of 15 micrograms per cubic meter.

Even more ominous: the risk of dying from a heart attack or ischemic stroke jumps a whopping 30 percent with each additional 10 micrograms of pollution.

Highway Danger

Particulate matter pollution at is highest close to expressways or truck routes, and is hard for commuters to avoid. They are exposed to the pollution inside a car, even with the windows rolled up, commuter trains or even just walking outdoors, Mutlu said. The only safe location with lower levels is indoors.

Those with previous blockages in the coronary or carotid arteries are at the highest risk. Exercising raises the risk since it fills the lungs with polluted air. “If you’re sitting down, the amount of air you get into your lungs is about five to six liters per minute, but if you’re running the amount is 20 to 25 liters,” Mutlu noted. “If you’re close to an expressway, you’re actually breathing more particulate matter into your lungs.”

The doctors also warned that heart attacks and strokes occur at relatively low levels of particulate matter pollution. “We haven’t found a safe level yet,” Mutlu said. He hopes the study helps encourages the EPA and local regulators to reduce the limits on particulate matter levels.


      1. Wellenius G.A., Bateson T.F., Mittleman M.A., Schwartz J. 2005. Particulate air pollution and the rate of hospitalization for congestive heart failure among Medicare beneficiaries in Pittsburgh, Pennsylvania. Am. J. Epidemiol. 161:10301036.

2. Wellenius G.A., Schwartz J., Mittleman M.A. 2005. Air pollution and hospital admissions for ischemic and hemorrhagic stroke among Medicare beneficiaries. Stroke. 36:25492553

3. Kishimoto T, Akira S, Narazaki M, Taga T (1995). “Interleukin-6 family of cytokines and gp130”. Blood 86: 1243-1254.

Image: Crystal structure of IL-6 as published in the Protein Data Bank- Creative Commons License