A long-term exposure to air pollution could increase risk of blood clots in deep veins by 39 to over 100 per cent, according to a study that followed over 6,650 adults in the US for 17 years.

Blood clotting conditions in deep veins are collectively known as 'venous thromboembolism', and if left untreated can block flow and cause serious complications.

Researchers, including those from the University of Minnesota, analysed data on patients hospitalised for venous thromboembolism and air pollution, collected through community-level monitoring, such as by taking samples from the participants' homes.

The adults in the study lived in or near six major metropolitan areas, including New York, Chicago and Los Angeles.

Of the group, 3.7 per cent (248 adults) were found to develop blood clots in veins located deep within the body, or deep veins, chances for which were linked to 39 per cent to over 100 per cent increase in risk due to exposure to PM2.5 and oxides of nitrogen. The findings are published in the journal Blood.

While exposure to higher levels of PM2.5 pollution could increase risk of venous thromboembolism by up to 39 per cent, people exposed to higher levels oxides of nitrogen and nitrogen dioxide could experience a 120-174 per cent increase in risk, the researchers found.

Being exposed to air pollution is known to increase risk of inflammation and contribute to blood clotting, which is in turn linked to cardiovascular and respiratory conditions.

The researchers said that this is the largest, most comprehensive study in the US reporting on the link between developing blood clots in deep veins and exposure to different types of air pollutants.

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