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Pollution A Risk Factor In Blood Clots, Study Finds

Loretta Fong, Bloomberg and Reuters – Updated on May 14, 2008

Hongkongers were warned yesterday to be alert to the risk of developing blood clots in their legs after research showed that air pollution could be a factor in the potentially fatal condition.

A Hong Kong University blood expert said that while the findings were not conclusive, they could be an indicator that the city should take notice of.

A Harvard University study, published in the Archives of Internal Medicine on Monday, is the first research into air pollution’s effects on clotting in the veins.

It suggested that long-term exposure to air pollution heavy in small particles might cause blood clots in the legs, similar to the condition known as deep vein thrombosis that affects air travellers.

Researchers examined 870 patients in Italy who had been diagnosed with deep vein thrombosis (DVT) in their legs from September 1995 to 2005, and compared their risk to another 1,210 people in a control group, who did not have DVT. The findings showed that for every increase in particulate matter of 10 micrograms per square metre in the previous year, the risk of deep vein thrombosis also went up 70 per cent.

Deep vein thrombosis forms in the vessels that carry blood back to the heart. Clots can break off and travel to the lungs, blocking blood flow there, possibly leading to lung damage or death.

Andrea Baccarelli, the study’s lead author and associate professor of environmental health at Harvard’s school of public health in Boston, said that doctors might wish to consider pollution as a new risk factor for clots.

James Chim Chor-sang, an associate professor in the department of medicine (haematology) at Hong Kong University, said the finding could be an indicator.

“Air pollution is a worldwide problem, as well as here in Hong Kong, so people should take notice of it,” he said.

But he added that it was too early to tell whether long-term exposure to particulate air pollution meant a higher risk of DVT.

“I believe another study should be done to confirm the association between the two,” he said.

“In the case of Hong Kong, it is also hard to say now as we are short of data on the number of people with DVT.”

He also noted that the incidence of DVT among Asians was 40 to 50 per cent less than people in western countries.

The green group Friends of the Earth said air pollution was already known as a risk factor in other conditions such as heart disease and lung ailments, and the government should work harder to control vehicle emissions.

Director Edwin Lau Che-feng said the most threatening particulate matter was roadside pollutants caused by heavy diesel vehicles, buses, container trucks and trucks.

“When you walk in the street, you can see black smoke coming out from the car pipes,” he said. “And since the streets in Hong Kong are packed, people such as street hawkers suffer a lot.”

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