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 microm 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 [beta] = -0.12; 95% confidence interval [CI], -0.23 to 0.00) (P = .04) and controls (beta = -0.06; 95% CI, -0.11 to 0.00) (P = .04). Each increase of 10 microg/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 PM10 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.