Long-term exposure to air pollution appears to be associated with an increased risk of deep vein thrombosis, blood clots in the thigh or legs, according to a report in the May 12 issue of Archives of Internal Medicine, one of the JAMA/Archives journals1.
Exposure to particulate air pollution—very small particles of solid and liquid chemicals that come from burning fossil fuels and other sources—has been linked to the increased risk of developing or dying from heart disease and stroke, according to background information in the article. Recent studies have suggested this relationship may result at least in part from the effects of particulate air pollution on blood clotting.
Andrea Baccarelli, M.D., Ph.D., of the Harvard School of Public Health,
Individuals with deep vein thrombosis tended to have a higher exposure to particulate air pollution than controls. After adjusting for other environmental and health factors, for every increase in particulate matter of 10 micrograms per square meter the previous year, the risk of deep vein thrombosis increased 70 percent. In addition, the blood of patients in both the case and control groups with higher levels of exposure to particulate matter took less time to clot, as measured by a test given in the clinic.
The association between particle exposure and blood clots was stronger in men than in women, and disappeared among women taking oral contraceptives or hormone therapy. “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,” the authors write.
“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,” they conclude.
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’,” writes Robert D. Brook, M.D., of the
“While we have learned to live within this haze without a second thought, air pollution is neither natural nor benign,” he continues. “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 deaths annually).”
Dr. Baccarelli and colleagues have presented evidence of a new category of health risks associated with pollution, he writes. “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,” Dr. Brook concludes.
1. Arch Intern Med. 2008;168:920-927.
2. Arch Intern Med. 2008;168:909-911.