Long-term exposure to air pollution and the risks of venous thromboembolism: a nationwide population-based retrospective cohort study.

Objectives: To delineate the effects of exposure to air pollution on the risk of venous thromboembolism (VTE).

Background: The association between air pollution and arterial occlusive diseases has been well reported in the literature. VTE is the third most common acute cardiovascular syndrome; however, its relationship with exposure to air pollution has been controversial.

Methods: This study linked data from the Taiwan National Health Insurance Research Database with that from the Taiwan Environmental Protection Administration. Patients who were first admitted for VTE between January 1, 2001, and December 31, 2013, were analyzed. A time-stratified, case-crossover design was employed. Three different exposure periods were defined: exposure for 1 month, one quarter, and 1 year. Four control periods were designated for each exposure period. The association between exposure to air pollutants and the risk of VTE was tested using logistic regression analysis. Subgroup analyses were also performed, stratified by age, sex, type of VTE, the use of hormone therapy, and level of urbanization at the site of residence.

Results: Exposures to particulate matter (PM) smaller than 2.5 µm (PM) and those smaller than 10 µm (PM) were associated with higher risks of VTE, with longer exposures associated with higher risk. The concentration of PM exposure for 1 month was linearly associated with a greater risk of VTE up to 28.0 µg/m, beyond which there was no association. PM exposure for one quarter or 1 year remained significantly associated with higher risks of VTE at higher concentrations. The increased risk in VTE associated with exposure to PM was more prominent in older patients and in patients not under hormone therapy. Similar results were observed for PM exposures.

Conclusions: Exposure to PM, particularly PM, leads to an increased risk of VTE, with possible accumulative effects. With increased PM production in industrializing countries, the effects of PM on VTE occurrence warrant further attention.