TUESDAY, May 15 (HealthDay News) -- With the 2012 Olympics set to begin in London this summer, a new study on air quality during the 2008 Beijing Olympics delivers an important public health message: Reducing air pollution levels could lower the risk of heart trouble for many.
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Four years ago, an international team of researchers took advantage of changes in air quality surrounding the 2008 Olympics, to see what health effects those changes might bring. The Chinese government had agreed to limit the use of motor vehicles and the operating hours of power plants in an effort to lower air pollution levels during the games. Once the international sporting event, and the accompanying restrictions, had ended, air pollution levels rebounded.
In the months before, during and after the 2008 Olympics, the researchers took measurements from 125 medical residents in Beijing, tracking their blood pressure and various biomarkers associated with heart disease. They found that rising air pollution levels drove up blood pressure and blood-clotting factors in the otherwise healthy medical residents.
"Studies have shown an association between air pollution and strokes or heart attacks," said study author Junfeng (Jim) Zhang, a professor of environmental and global health at the University of Southern California. "[But] they have not really looked into what we have addressed, which is how air pollution affects the heart."
"If pollution continues, and the burdens of blood-clotting factors are kept at elevated levels, I think there will be adverse consequences long-term," including increases in heart attacks, strokes and cardiovascular deaths, Zhang added.
The study was published May 16 in the Journal of the American Medical Association.
The researchers followed the medical residents, whose average age was 24, at a hospital in central Beijing. The participants were healthy and were not smokers, reducing the chance that they might experience illness unrelated to pollution during the study, Zhang said.
The team measured heart rate, blood pressure and blood levels of biomarkers for each participant twice in the beginning of the summer before the games, twice during the two months spanning the Olympics, and twice in the fall after the games.
During those months, the researchers also monitored the daily level of air pollutants, including particulate matter, ozone and carbon, in samples taken from the hospital campus where the residents worked.
Two of the three biomarkers for blood clotting that the researchers measured, called von Willebrand factor and CD62P, decreased in the two months of the Olympic games. And the levels of one of them, CD62P, went back up after the Olympics.
The researchers also found a post-Olympics increase in the participants' systolic blood pressure -- the top number in a blood pressure measurement -- which has also been associated with heart disease and stroke.
"It was a surprise to see big changes in the two blood-clotting markers because we thought inflammatory markers might be more important," Zhang said.
The researchers did not see a statistically significant change in indicators of inflammation, like white blood cell count and C-reactive protein. However, Zhang said he suspects that if the researchers had included a couple hundred more people, they would have seen changes in inflammatory markers.
It is not clear from the study which of the pollutants might be driving the changes in the blood-clotting factors and blood pressure; the levels of nearly all of the pollutants that the team measured dropped during the Olympics and went back up in its aftermath.
"It has proven difficult to figure out which is most toxic," explained Michael Jerrett, a professor of environmental health sciences at University of California, Berkeley.
Instead, researchers tend to think a mix of pollutants that includes particulate matter, carbon and nitrogen dioxide are the most dangerous. "If we were to reduce carbon dioxide, we are going to get benefits in terms of reduced levels of other pollutants that are strongly associated with health effects," Jerrett explained.
"Showing that you can achieve these major [pollution] reductions if you are willing to put these controls in place is an important finding in and of itself," Jerrett added.
Previous research has found that decreases in particulate matter in the United States during the 1980s and 1990s were responsible for 15 percent of the increase in life expectancy during this period.
A lot of the pollution-control measures undertaken by the United States and other wealthy industrialized countries for the past 30 years were "low-hanging fruits, and measures now are quite costly," Jerrett added. "People making these decisions want to have certain evidence, and I think this study adds to the body of evidence of the potential health benefits."
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SOURCES: Junfeng (Jim) Zhang, Ph.D., professor, environmental and global health, Keck School of Medicine, University of Southern California, Los Angeles; Michael Jerrett, Ph.D., chair, professor, environmental health sciences, School of Public Health, University of California, Berkeley; May 16, 2012, Journal of the American Medical Association