Using the 2008 Beijing Olympics as their
laboratory, University of Southern California (USC) researchers and colleagues
have found biological evidence that even a short-term reduction in air
pollution exposure improves one's cardiovascular health.
The
results of their study appear this week in the Journal
of the American Medical Association, the most widely circulated medical
journal in the world.
"We
believe this is the first major study to clearly demonstrate that changes in
air pollution exposure affect cardiovascular disease mechanisms in
healthy, young people," said Junfeng (Jim) Zhang, Ph.D., the study's
senior author and professor of environmental and global health at the Keck
School of Medicine of USC.
Beijing,
plagued by chronic air pollution, was awarded the 2008 Summer Olympics after
promising to improve air quality for the duration of the event. Spending $17
billion on environmental cleanup, the government shut down factories and
limited automobile traffic from July 20 to Sept. 17 to encompass the entire
Olympic (Aug. 8-24) and Paralympic (Sept. 6-17) games. Pollution control
measures relaxed after the Paralympics.
"Beijing
is one of the most polluted cities in the world, and the Chinese government had
proposed to reduce pollution levels to
be comparable to other Olympic host cities," Zhang said. "We wanted
to take advantage of such a huge intervention and look at what happens to
people biologically."
Zhang's
team, which included scientists from the University of Rochester, University of
Medicine and Dentistry of New Jersey and Peking University in Beijing,
recruited 125 male and female resident doctors who worked at a central Beijing
hospital, all of whom were never-smokers and disease-free. The participants,
whose average age was 24, visited the clinic six times: twice prior to the air
pollution controls, twice while the pollution controls were in play and twice
after the games had ended.
The
researchers examined biomarkers for systemic
inflammation and blood clotting, as well as heart rate and blood
pressure. During the Olympics, they observed statistically significant
reductions in Von Willebrand factor and soluble CD62P levels, both of which are
associated with blood coagulation, among the study participants. Soluble CD62P
and systolic blood pressure levels also increased significantly after the
Olympics.
These
changes indicate that exposure to higher air pollution levels are associated
with an increased risk for cardiovascular problems. Changes among other
measured indicators that support this association were also observed, although
not statistically significant.
"Changes
in cardiovascular physiology and inflammation contribute to the instability of
atherosclerotic plaques, which can lead to a heart attack or stroke if
ruptured," Zhang said. "The changes in Von Willebrand factor and
soluble CD62P are consistent with their roles in rapid thrombotic
response."
Each
biomarker observed in the study has been related to cardiovascular morbidity or
mortality in clinical studies, but few studies have considered how the
environment affects the markers. In fact, it is only recently that population
studies have linked air pollution exposure to risk for cardiovascular
disease, according to Jonathan Samet, M.D., professor and Flora L. Thornton
Chair of the Keck School's Department of Preventive Medicine. This new study
offers important evidence that air pollution exposure harms the health of the
public, adds Samet, chairman of the Environmental Protection Agency's Clean Air
Scientific Advisory Committee.
"This
study shows how air pollution exposure may
act to increase cardiovascular disease risk, supporting the more general
findings on air pollution and this very important group of diseases," said
Samet, who also is director of the USC Institute for Global Health. "We
need to remember that large numbers of people in cities around the world are
still exposed to high levels of air pollution as they are in Beijing."
The
study underscores the fact that people's health and the environment are
indelibly linked, says Caroline Dilworth, Ph.D., program administrator from the
National Institute of Environmental Health Sciences (NIEHS), which provided
funding for the study.
"When air pollution levels
are lowered, the health benefits can be immediate," Dilworth said.
Other
USC co-authors include post-doctoral research associate Jicheng Gong, Ph.D.,
and Duncan Thomas, Ph.D., a professor of preventive medicine. The study was
jointly funded by the NIEHS, Health Effects Institute, Beijing Municipal Bureau
of Environment Protection and Beijing Council of Science and Technology.
More
information: Rich,
D.Q., Kipen, H.M., Huang, W., Wang, G., Wang., Y., Zhu, P., Ohman-Strickland,
P., Hu, M., Philipp, C., Diehl, S.R., Lu, S., Tong, J., Gong, J., Thomas, D.,
Zhu, T., & Zhang, J. (2012). Association between changes in air pollution
levels during the Beijing Olympics and biomarkers of inflammation and
thrombosis in healthy young adults. Journal of the American Medical
Association, 307(19), 2068-2078. Published online May 15, 2012.
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