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.
"These factors basically predict blood-clotting potential," Zhang said. "The higher their levels, the greater the possible risk of heart attack and stroke."
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
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