(May 12, 2008 - Insidermedicine) Exposure to small particles of pollution in the air increases the risk of developing blood clots in the legs and thighs, according to research published in the Archives of Internal Medicine.

Here are some facts about air pollution from the World Health Organization:

•    The primary source of outdoor air pollution is the combustion of fossil fuels, such as oil and coal.

•    Outdoor air pollution is a worldwide problem that is particularly serious in large cities. An estimated 25% of the world population – over a billion people – are exposed to unhealthy levels of air pollution.

•    Outdoor air pollution contributes to the development of several conditions that affect respiration; children are at particularly high risk.

Researchers from the Harvard School of Public Health compared the amount of exposure to small particle air pollution among two groups of individuals living in Lombardy, Italy: nearly 900 individuals with blood clots in the leg or thigh and over 1,200 individuals without this condition. Pollution exposure was estimated using average ratings from monitors that were set up at 53 different sites.

Overall, those with leg and thigh clots tended to have more exposure to small particle air pollution over the previous year than those without the condition. Higher exposure to pollution was also linked with having blood that clotted more quickly, particularly among men. Fast clotting blood is associated with an increased risk for conditions that include heart attack and stroke.

Today's research provides a new incentive to curb air pollution. Newly identified effects of small particle air pollution on human health include a risk for blood clots in the legs and thighs and the tendency for the blood to clot faster, which may have other negative health implications.

For Insidermedicine in Depth, I'm Dr. Susan Sharma.