It has long been known that pollution has noxious repercussions on our health, but no study stated that it might raise the risk of deep vein thrombosis (DVT) until today.

Deep vein thrombosis is a blood clot that forms in vein in the body. Blood clots occur when blood thickens and clumps together. Most deep vein blood clots occur in the lower leg or thigh. They also can occur in other parts of the body. What makes a blood clot dangerous is that it can travel through the bloodstream to different organs of the body. The loose clot is called an embolus. When it travels to the lungs for example, it blocks blood flow causing pulmonary embolism. It can also cause heart attack or stroke.

According to the Society of Interventional Radiology, about 600,000 new patients are diagnosed as having DVT every year and one in 100 of these people dies.

Harvard researcher Andrea Baccarelli, MD, PhD, and colleagues in Italy analyzed 870 people diagnosed with DVT from 1995 to 2005. They compared their particulate air pollution exposure in the year before their diagnosis to that of 1.210 matched people without DVT.

The researchers found that individuals with DVT tended to have a higher exposure to particulate air pollution than controls. To be more specific, they found that for every 10 micrograms per square meter increase, the risk of developing DVT went up by 70 percent. Men were more likely than women to suffer from exposure to polluted air.

“Given the magnitude of the observed effects and the widespread diffusion of particulate pollutants, our findings introduce a novel and common risk factor into the pathogenesis of deep vein thrombosis, and, at the same time, give further substance to the call for tighter standards and continued efforts aimed at reducing the impact of urban air pollutants on human health,” the researchers concluded.

In an editorial accompanying the study in the May 12 issue of Archives of Internal Medicine, Robert D. Brook, M.D. of the University of Michigan warns that air pollution “has become so omnipresent over the past century as to be commonly perceived as a normal natural entity – ‘the lazy, hazy days of summer’.”

Air pollution from automobiles and industry can contain tiny particles of carbon, nitrates, metals and other materials that have been linked over the years to a variety of health problems.

In a study published in the Journal of Epidemiology and Community Health last month, researchers from Birmingham University studied atmospheric emissions in England for the period 1996-2004 and attributed some 4,000 extra pneumonia deaths each year to engine pollution, which is the same number of people killed during the infamous weeklong London smog of December 1952.

Pollution was also linked to higher rates of some cancers, chronic obstructive pulmonary disease and rheumatic heart disease.

“While we have learned to live within this haze without a second thought, air pollution is neither natural nor benign. Even though the absolute cardiovascular risk posed to one individual at any single time point is small, owing to the ubiquitous and constant nature of exposure, particulate matter ranks as the 13th leading cause of global mortality (approximately 800,000 death annually),” Brook warns in his editorial adding that about 800,000 people die every year because of pollution-related illness.