Air Pollutants Mediate Effects on Heart Health Through Inflammation and Thrombosis

May 17, 2012

May 16, 2012 (Los Angeles, California) — Changes in air-pollution levels in China during the 2008 Olympic Games resulted in a reduction in biomarkers of inflammation and thrombosis, as well as other measures of cardiovascular physiology, a new study has shown [1]. The Chinese policy of restricting air-pollution emissions during the Olympics allowed researchers to assess the acute effects of air pollution, which resulted in reductions in von Willebrand factor and soluble P-selectin, two markers of platelet adhesion and activation, as well as C-reactive-protein (CRP) levels.

"The common wisdom among many people is that air pollution is bad for your lungs, and also many people know that air pollution can affect the heart as well, but they think it only affects old people with preexisting cardiovascular or other health conditions," senior investigator Dr Junfeng (Jim) Zhang (University of Southern California, Los Angeles) told heartwire . "It might not be a concern for the young and healthy. But in this study, we really show that air pollution can clearly affect a young and healthy heart. It really tells us that everybody is affected by pollution."

In addition, Zhang said the study, which tested the effects of pollution on 125 healthy medical residents, highlights how sensitive the human body is to pollution changes. The physiological changes in response to shifts in air pollution can be detected within a very short period of time, and this means that even short-term interventions, such as those performed in Beijing, can bring immediate health benefits to healthy people, he said.

The results of the study are published in the May 16, 2012 issue of the Journal of the American Medical Association.

A Quasi-Experimental Study of Air Pollution

To date, data from epidemiological studies have linked air-pollution levels with cardiovascular morbidity and mortality. In addition to the limitations of epidemiological evidence, Zhang said the underlying biological mechanisms linking air pollution to cardiovascular disease events are unknown. The present study was designed to determine whether the "logical pathways," such as systemic inflammation and thrombosis, would help explain the association between pollution and cardiovascular morbidity and mortality.

In 2008, as a condition for hosting the Olympic and Paralympic Games, the Chinese government agreed to a series of aggressive pollution-control measures to temporarily improve air quality in Beijing. The move saw the operation of industrial and commercial combustible facilities in Beijing substantially limited and the use of alternate-day driving to remove approximately 1.5 million cars from the roads each day. The measures were implemented one month prior to the Olympics and ran until the completion of the Paralympic Games.

"If you want to have an experimental study in the laboratory, you're going to have a high-pollution condition and a low-pollution condition, but this is very limited, usually to small-scale animal studies," said Zhang. "In the real world, it's really very rare to come up with an opportunity like the Beijing Olympics afforded us, with the massive controls the Chinese government implemented to improve the air quality."

With these instituted air-pollution-control measures, the mean concentration of sulfur dioxide decreased 60%, carbon monoxide 48%, nitrogen dioxide 43%, elemental carbon 36%, PM2.5 27%, organic carbon 22%, and sulfate 13% from the pre-Olympic period to measurements taken during the Olympics. The pollutant concentrations tended to increase again once the control measures were removed, with the exception of ozone and sulfate.

The researchers measured soluble P-selectin (sCD62P), soluble CD40 ligand (sCD40L), and von Willebrand factor, all of which are validated markers of platelet activation and endothelial dysfunction, and CRP and fibrinogen concentrations. There were significant decreases in sCD2P and von Willebrand factor and a nonsignificant reduction in sCD40L, heart rate, and systolic and diastolic blood pressure from the before- to the during-Olympic period. CRP, measured as a fraction of the above-detection-limit value (>0.3 mg/L), was reduced from 55% during the pre-Olympic period to 46% during the Olympics.

Biomarker Concentrations by Period and Between-Period Changes, Adjusted for Temperature and Relative Humidity

Biomarker Before During After Change from before Olympics to during Olympics (%) p Change from during Olympics to after Olympics (%) p
sCD62P, ng/mL 6.29 4.16 5.36 -34.0 <0.001 33.7 <0.001
sCD40L, ng/mL 1.86 1.76 1.92 -5.7 0.03 9.1 0.17
Von Willebrand factor (%) 106.4 92.6 79.5 -13.1 <0.001 -14.2 0.19
Heart rate, min 66.5 65.4 66.1 -1.7 0.04 1.1 0.54
Fibrinogen, mg/dL 250 250 261 0.1 0.90 4.3 0.21
Systolic blood pressure, mm Hg 102.5 100.9 110.5 -1.8 0.10 10.7 0.01
Diastolic blood pressure 60.2 60.1 60.1 -0.3 0.86 0.1 0.99
White blood cell count, µL 5290 5400 5210 2.2 0.34 -3.9 0.44

"The inflammatory markers were very much expected because animal studies in laboratory have shown that inflammation is a principal pathway for air-pollution–induced adverse health effects," said Zhang. "We were nicely surprised by the blood clotting markers."

To heartwire , Zhang said that the strict air-pollution controls implemented by the Chinese government included many different actions, but 80% of the improvement in air quality is likely attributable to traffic control. Cities in developing countries are experiencing a rapid growth in the number of cars on the streets, and while the primary concern in these cities is gridlock, efforts that would encourage carpooling and the use of public transportation could have large, widespread health benefits. "I know it's not easy to drive less, but it would be good for everybody's health," said Zhang.

In an editorial accompanying the study [2], Drs Francesca Dominici and Murray Mittleman (Harvard School of Public Healthy, Boston, MA) state that the study provides new data and evidence of pollution in "one of the most rapidly developing and polluted cities in the world, with a complex political and economic landscape." Of the 800 000 deaths and 4.6 million lost years of healthy life caused by pollution, two-thirds occurred in Asia. In fact, average annual PM2.5 concentration in Beijing is nearly eight times higher than the proposed annual US ambient-air-quality standard of 15 µg/m3. "China's dilemma, like many countries with emerging industries, is how to reconcile rapid economic growth with environment protection," write the editorialists.

This study was jointly funded by grants from the National Institute of Environmental Health Sciences, the Health Effects Institute, the Beijing Environment Protection Bureau, and the Beijing Council of Science and Technology. The authors reported that they have no conflicts of interest.

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