Association between particulate air pollution and venous thromboembolism: A systematic literature review

Air pollution is a leading global problem for public health. A number of ambient pollutants have been involved, including carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3) and particulate matter (PM). Although exposure to PM has been linked to a wide array of cardiovascular and respiratory disorders, its effect on venous thrombotic disorders is still uncertain. To elucidate this issue, we have performed a systematic review on the existing literature on the association between PM and venous thromboembolism (VTE), using MEDLINE, EMBASE and Cochrane electronic databases. Of the 158 reviewed studies, 11 of them (3 case-crossover studies, 2 time-series studies, 2 case-control studies, 2 prospective cohort studies, 2 retrospective studies) involving more than 500,000 events fulfilled the inclusion criteria and results are presented here. Because there was substantial heterogeneity in study design, duration of follow-up, statistical measure of effects, clinical outcomes and threshold, we refrained to perform a quantitative analysis of the available data and carried out only a systematic review. Overall, the literature data suggest a link between PM and VTE, but further trials on larger populations of patients with homogeneous study designs and outcomes are warranted.