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Air Pollution Ups Risk of Deep Vein Thrombosis

Long-term exposure to very small particles of liquid and solid chemicals in the air have been shown to be associated with an increased likelihood of developing deep vein thrombosis, a condition that can become deadly when left untreated. The danger of deep vein thrombosis, which is characterized by blood clots in the veins of the thigh and leg, comes when a clot dislodges from the leg and travels to the lungs, where embolism can cause sudden death.

The particulate matter in the air comes from the burning of fossil fuels and other means of air pollution associated with modern-day living and particles smaller than 10 micrometers are linked to the development of deep vein thrombosis, as well as to the risk of cardiovascular disease and death. The longer the exposure or more intense the pollution, the higher the likelihood of developing the condition.

A Harvard School of Public Health team of researchers in Boston used data from Lombardy, Italy, to assess the link between deep vein thrombosis and common air pollution. The team reviewed records dating from 1995 to 2005 covering 870 patients with deep vein thrombosis and a control group of 1,210 who had been examined for deep vein thrombosis but who didn’t have the condition.

In addition to medical records and personal data, the group incorporated data from 53 different air-quality monitoring sites throughout the Lombardy region to assess exposure levels during the year before diagnosis or exam.

The research team, led by Harvard’s Andrea Baccarelli, MD, PhD, found that every increase of 10 micrograms per square meter of particulate air pollution generated an increase in the risk of developing deep vein thrombosis by 70%.

An additional finding of the study was that exposure to particulate air pollution led to faster clotting time in the study participants’ blood. Clotting time was tested during visits to healthcare facilities. The men in the study seemed to be the most adversely affected by the air pollution, as measured by both the incidence of deep vein thrombosis and accelerated clotting time.

Women in the study enjoyed less risk of developing either condition unless they were undergoing hormone therapy or taking oral contraceptives, both of which are known to affect clotting. When using either hormone treatment, the risk of the women developing deep vein thrombosis and of accelerated clotting closely matched that of the men.

People in general have come to accept air pollution as an annoying but expected by-product of modern life but the true health consequences are still being discovered. Exposure to particulate matter in the air is the number 13 cause of death globally, killing almost 800,000 people each year.

The findings of the Harvard study can be found in the May 12 issue of JAMA and Archives Journals. Funding for the study was provided by the Environmental Protection Agency’s Particulate Matter Center, the National Institute of Environmental Health Sciences, the MIUR Internationalization Program, the CARIPLO Foundation, and the Lombardy region.

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