Air pollution may cause deadly blood clots in legs

[Karl]

ScienceNOW – 12 May 2008

Already linked to heart and lung problems, smog could pose a bigger threat to our well-being than previously thought. Researchers report today that air pollution may cause potentially deadly blood clots in the legs. Experts say the finding highlights the need for stricter regulations to keep pollutants in check.

People breathing high levels of air pollution from coal-burning factories, car and truck exhaust, and other sources are more likely to suffer a heart attack or stroke (ScienceNOW, 11 March 2002). Researchers think these health problems result from microscopic flecks in the pollution called particulate matter that, when inhaled into the lungs, can make their way into the bloodstream and induce clots. If that's the case, the pollution particles could also cause deep vein thrombosis, a potentially fatal condition triggered by blood clots in veins of the legs that strikes 2 million Americans each year. But nobody had ever looked for a link between the two.

A team led by Joel Schwartz, an environmental epidemiologist at Harvard University, used air monitors to zero in on particulate matter's role in triggering deep vein thrombosis. The scientists tested 870 patients in Italy's Lombardy region who had been diagnosed with the condition between 1995 and 2005. Air monitors showed that during the year before their diagnosis, the patients lived in areas with higher levels of particulate matter than did control subjects who did not develop clots. The higher the level of exposure, the greater the risk of deep vein thrombosis. The heightened risk remained even after taking into account factors that could increase the susceptibility to developing deep vein thrombosis, such as age, education, area of residence, and weight. Subjects breathing in the average level of particulate matter detected in this study had a 10 times higher risk of developing deep vein thrombosis than did those with the lowest exposure, the researchers report in the Archives of Internal Medicine. The blood from patients with average exposure levels also clotted faster, suggesting that the pollution particles somehow trigger coagulation.

Researchers don't know how the pollution particles cause blood clots. But Schwartz says one possibility is that after they are inhaled into the body, the particles induce inflammation on the insides of veins and arteries, which then leads to clot formation. Robert Brook, a cardiologist at the University of Michigan, Ann Arbor, who was not involved in the research, notes that some western cities, such as Mexico City and areas of Los Angeles, reach the average particulate-matter level in the study, whereas urban areas in the Middle East and Asia, such as Beijing, China, exceed it. "The whole burden of air pollution may be much greater than we've previously thought," he says. If inflammation induced by pollution particles is an underlying cause of deep vein thrombosis, Brook adds, the health impact of pollution could be even higher. Particulate matter could trigger or worsen a variety of other conditions in which inflammation plays a role, he says, including high blood pressure, diabetes, and even neurological disorders such as Alzheimer's disease. Clive Pope, an environmental epidemiologist at Brigham Young University in Provo, Utah, sees a silver lining in the pollution cloud. The findings suggest that more stringent air pollutant regulations could help reduce the risk of deep vein thrombosis, he says.

Source: Beware the Air -- Mitchell 2008 (512): 4 -- ScienceNOW