Air Pollution Triggers Blood Clots - US Study
Author: Julie Steenhuysen
Large population studies have shown pollution from the
exhaust of trucks, buses and coal-burning factories increases
the risk of fatal heart attacks and strokes.
But researchers have not understood how these microscopic
particles actually kill people.
"We now know how the inflammation in the lungs caused by
air pollutants leads to death from cardiovascular disease,"
said Dr. Gokhan Mutlu of Northwestern University in Chicago,
who studied the effects of air pollution in mice.
Lungs inflamed by pollution secrete interleukin-6, an
immune system compound that sparks inflammation and has been
shown to make blood more likely to clot.
The research appears in the Journal of Clinical
Investigation. It follows a study last week in the New England
Journal of Medicine that found breathing diesel fumes
interfered with heart attack survivors' ability to break down
Mutlu got a clue about the clotting issue two years ago
when he was studying the effects of air pollution on heart
failure in mice. Mice who had been exposed to pollution bled
"They were forming blood clots," he said in a telephone
In the latest study, he and colleagues exposed mice to
particles of air pollution collected by the US Environmental
Protection Agency. These were mixed with a saline solution and
injected into the lungs of mice.
Mice exposed to pollution showed a 15-fold increase in
interleukin-6 just 24 hours later. That time frame is important
because some studies have shown a spike in air pollution can
boost heart attacks with 24 hours.
Mutlu and colleague Dr. Scott Budinger said they were able
to prevent this clotting by suppressing immune cells in the
lungs called macrophages that attack foreign substances and
Mice with suppressed immune responses did not show
increased blood clotting. "This suggested that interleukin-6
was the driving force," Mutlu said.
He said most people understand that high levels of air
pollution can make lung diseases such as asthma worse.
"The same thing is not known for patients with coronary
artery disease or congestive heart failure," Mutlu said. "I
think we need to increase the awareness of this link among
The researchers now plan to study whether aspirin can
counteract the clotting effect in mice. Low-dose aspirin helps
thin the blood and is already recommended for people with heart