Exposure to particulate air pollution and risk of deep vein thrombosis

Background: Particulate air pollution has been linked to heart disease and stroke, possibly resulting from enhanced coagulation and arterial thrombosis. Whether particulate air pollution exposure is related to venous thrombosis is unknown. Methods: We examined the association of exposure to particulate matter of less than 10 μm in aerodynamic diameter (PM₁₀) with deep vein thrombosis (DVT) risk in 870 patients and 1210 controls from the Lombardy region in Italy, who were examined between 1995 and 2005. We estimated exposure to PM₁₀ in the year before DVT diagnosis (cases) or examination (controls) through area-specific mean levels obtained from ambient monitors. Results: Higher mean PM₁₀ level in the year before the examination was associated with shortened prothrombin time (PT) in DVT cases (standardized regression coefficient [β]=-0.12; 95% confidence interval [CI], -0.23 to 0.00) (P=.04) and controls (β=-0.06; 95% CI, -0.11 to 0.00) (P=.04). Each increase of 10 μg/m3 in PM₁₀ was associated with a 70% increase in DVT risk (odds ratio [OR], 1.70; 95% CI, 1.30 to 2.23) (P<.001) in models adjusting for clinical and environmental covariates. The exposure-response relationship was approximately linear over the observed PM₁₀ range. The association between PM₁₀ level and DVT risk was weaker in women (OR, 1.40; 95% CI, 1.02 to 1.92) (P=.02 for the interaction between PM ₁₀ and sex), particularly in those using oral contraceptives or hormone therapy (OR, 0.97; 95% CI, 0.58 to 1.61) (P=.048 for the interaction between PM₁₀ level and hormone use). Conclusions: 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.