Traffic pollution can be deadly as it increases the risk of deep vein thrombosis

Scientists in the U.S. have confirmed a long held suspicion that traffic pollution can be deadly for some people.

The scientists from Harvard School of Public Health have found that breathing in air pollution from traffic fumes can raise the risk of potentially deadly blood clots forming in the body.

They say the tiny particulates found in exhaust fumes contain chemicals caused by burning fossil fuels which are known to increase the chances of heart disease and stroke but they also have an impact on the development of deep vein thrombosis (DVT) - blood clots in the legs.

The study examined over 2,000 people living in Lombardy, Italy, between 1995 and 2005, and found that the pollution made the blood more sticky and likely to clot and 870 of them developed DVT.

The risk of DVT is known to be increased by long periods of immobility, particularly in the case of passengers on long-haul flights.

But also vulnerable are people who spend long periods sitting at desks without exercising, or walking around - blood clots which form in the legs can travel to the lungs, where they can become lodged, triggering a potentially fatal pulmonary embolism.

By examining pollution readings from the areas where the study participants lived, the researchers found those exposed to higher levels of small particulates in the year before diagnosis were more likely to develop blood clots.

They found for every 10 microgrammes per square metre increase in small particulates, the risk of developing a DVT went up by 70%.

Guidelines regarding air quality guidelines usually advise that small particulate concentrations should not exceed 50 microgrammes.

Dr. Andrea Baccarelli who led the study says the findings introduce a new but common risk factor into the development of DVT and lend support to calls for tighter standards and continued efforts to reduce the impact of urban air pollutants on human health.

The researchers say the link between particle exposure and blood clots was stronger in men than in women, and disappeared among women taking oral contraceptives or hormone therapy.

They also say such hormone therapies are themselves risk factors for deep vein thrombosis, which was also confirmed in the study by the higher prevalence of oral contraceptive and hormone use in the DVT cases compared with the controls.