Study During Beijing Olympics Shows How Pollution Harms the Heart

Inflammation and unhealthy clotting factors decreased in Beijing as pollution levels dropped during the 2008 Olympic Games. In order to maintain that trend, a researcher has some advice: drive less.

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Bad air means bad health, but just how harmful can pollution be to your heart? And exactly how do pollutants weaken the heart? The Beijing Olympics provides a clue.

Researchers reporting in the Journal of the American Medical Association provide the first evidence that even over the span of a few weeks or months, air pollution can affect key markers of heart health, including blood pressure and levels of enzymes and other proteins that track the viability of blood vessels. And they provide a window into how poor air quality can affect blood vessels and body processes that promote disease.

Although many studies have raised the alarm about the connection between pollution and an increased rate of heart attack and stroke, these analyses have suffered from one key weakness: how could the researchers know for sure that the rise in heart problems was primarily driven by pollution and not some other factor?

(MORE: Exposure to Air Pollution in Pregnancy May Boost Chances of Obesity in Kids)

So when the Chinese government committed to cleaning up the air in Beijing prior to the Olympic Games in 2008, scientists saw a unique opportunity to study how such a change might affect key heart health factors. The idea was to track changes in these markers before, during and after the Games.

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Beginning about two months before the Olympics, a team of researchers led by Junfeng (Jim) Zhang, professor of global and environmental health at the University of Southern California, recruited 128 medical students to provide blood samples. The specimens were tested for about 20 well-known markers of heart disease. These included proteins and enzymes related to inflammation, such as C-reactive protein, and substances associated with blood clotting, including fibrinogen and von Willenbrand factor; the scientists also took the participants’ blood pressure and measured their white blood cell counts. The post-Olympic period extended to about a month beyond the Games, when normal traffic patterns and presumably average air pollution levels began to rise again to pre-Games levels.

(MORE: The 10 Most Air-Polluted Cities in the U.S.)

Indeed, during the Olympics, the researchers recorded a 60% drop in sulfur dioxide, a 48% reduction in carbon monoxide and a 43% lower nitrogen dioxide level from the pre-Olympic period to the period spanning the Games. At the same time, they recorded changes in the levels of some of the inflammatory and clotting factors; they tended to drop when air quality was improved during the Games and increase as pollution levels rose again after the Olympics. Heart rates on average came down about 1 beat per minute in the pre-Olympics to during-Olympics period, while systolic blood pressure dropped by about 2mm Hg during the same time.

“This study shows that among healthy young people with no confounding factors such as being sick, [there are] changes that pollution can make day to day,” says Zhang. “Among healthy people, these markers should be pretty stable; blood pressure should not increase daily. But we see these changes, and we know that during the Olympics, air pollution was reduced. So this really affects young people. If we detect these changes in the young, imagine how harmful pollution is to the ones who have compromised hearts, or the elderly who might be more sensitive to pollutants.”

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What particularly surprised Zhang and his colleagues was how revealing the results were regarding the effect of pollution on the heart. While many studies have pointed the finger at inflammation, which can aggravate blood vessels and generate unstable plaque that can rupture, the current study also shows that blood clotting might be another way that bad air can damage the heart. With more pollution, the researchers saw higher levels of clotting factors such as fibrinogen, which can build up and occlude blood vessels, setting the stage for a heart attack.

With a deeper understanding of how pollutants are harming the heart, Zhang says policy makers should have a stronger appreciation for how important clean air regulation is for health. “We should encourage people to drive less,” he says. “In a big city like Beijing, that’s an important public policy message. I hope this study sends out that message.”

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.