New research on people living in Italy, suggests that long term exposure to air pollution is linked to an increased risk of deep vein thrombosis and blood clots in the legs or thighs, adding to previous research findings linking particulate air pollution and increased risk of death from cardiovascular diseases.
The study is published in the May 12th issue of the Archives of Internal Medicine and is the work of Dr Andrea Baccarelli, from the Harvard School of Public Health in Boston, US, and colleagues from other research centres in Italy and the US.
Air pollution comprises small particles and fine droplets of chemical matter produced from burning fossil fuels and other sources. Previous research has linked increasing concentrations of particulate air pollution with increased risk of heart disease and stroke, and scientists have suggested this could be due to the particles causing blood coagulation and arterial thrombosis, wrote the authors in their background information.
Baccarelli and colleagues obtained data on 870 deep vein thrombosis (DVT) patients from the Lombardy region of Italy who had been diagnosed between 1995 and 2005 and matched them to 1,210 controls who did not have DVT.
Then they assessed the patients’ exposure to particulate air pollution in the year before their diagnosis, and for controls, the year before their examination. They used measured mean levels of particles smaller than 10 micrometers in diameter (PM10) obtained from pollution monitors located in 53 different sites within the nine geographic areas where the patients and controls lived.
The results showed that:
- Individuals with DVT tended to have a higher exposure to PM10 air pollution particles than controls.
- There was a significant link between higher mean PM10 particle levels and shortened prothrombin time (PT, a measure of blood clotting tendency) in DVT cases .
- After adjusting for other environmental and health factors, for every increase in PM10 concentration of 10 micrograms per cubic metre in the year before diagnosis, the risk of DVT increased by 70 per cent.
- The link between PM10 level and DVT risk was stronger in men than women, and went away among women on oral contraceptives or on hormone therapy.
On the effect of hormone therapy and contraceptives, the authors wrote that “Such hormone therapies are independent risk factors for deep vein thrombosis, which is also confirmed in this study by the higher prevalence of oral contraceptive and hormone use in the cases compared with the controls.”
They concluded that:
“Long-term exposure to particulate air pollution is associated with altered coagulation function and DVT risk. Other risk factors for DVT may modulate the effect of particulate air pollution.”
They said their findings “introduce a novel and common risk factor into the pathogenesis of deep vein thrombosis,” and add weight to the case for tighter controls to reduce urban air pollution.
In an accompanying editorial titled “Blood Clot Risk Could Increase Estimates of Death Toll from Pollution”, Dr Robert D Brook of the University of Michigan, Ann Arbor, wrote 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.”
But he adds that, “While we have learned to live within this haze without a second thought, air pollution is neither natural nor benign.”
Although at any one point in time the absolute risk to one person’s cardiovascular health posed by particulate air pollution is minute, it is the constant, ubiquitous nature of the exposure that places it at 13th place among the world’s biggest killers, accounting for around 800,000 deaths a year, wrote Brook, who added that this study sheds light on a new risk posed by air pollution.
“If future studies corroborate their findings and address some of the limitations, it may be proven that the actual totality of the health burden posed by air pollution, already known to be tremendous, may be even greater than ever anticipated”, he concludes.
“Exposure to Particulate Air Pollution and Risk of Deep Vein Thrombosis.”
Andrea Baccarelli; Ida Martinelli; Antonella Zanobetti; Paolo Grillo; Li-Fang Hou; Pier A. Bertazzi; Pier Mannuccio Mannucci; Joel Schwartz
Arch Intern Med. 2008;168(9):920-927.
Vol. 168 No. 9, May 12, 2008
Sources: Journal abstract and JAMA press release.
Written by: Catharine Paddock, PhD