More on air pollution and venous thromboembolism

We read with interest the letter by Vreugdenhil [ ] who, referring to our systematic review recently published in this Journal on the association between particulate matter (PM) and venous thromboembolism (VTE) [ ], further strengthens the close link existing between exposure to air pollution and risk of developing cardiovascular diseases and cancer. His letter, which provides also possible solutions to the deleterious effects on health of PM, gives us the opportunity to offer some additional considerations. Venous thromboembolism, a life-threatening disorder with an estimated yearly incidence ranging from 0.8 to 2.7 per 1000 individuals [ ], is a multifactorial disease which usually develops from a combination of genetic and environmental risk factors [ ]. The overall worldwide morbidity and mortality associated to thrombosis are very significant, and VTE causes a major burden of disease across all socioeconomic classes and in low-, middle- and high-income countries [ ]. Recent evidences have suggested a positive correlation between VTE and air particulate matter [ ] and such clinical association has a well-documented biological plausibility, which includes PM-induced platelet activation and increased plasma levels of several coagulation factors involved in primary and secondary hemostasis [ , ]. However, a crucial question is: how many VTE cases occurring yearly are due to air pollution exposure? Unfortunately, as evidenced by our recent systematic review [ ], it is not currently possible to give an answer to this question. Nevertheless, although the wide inter-study heterogeneity and the paucity of well-designed prospective trials prevented an accurate quantification of this risk [ ], our impression arising from the qualitative analysis of the published literature data was clearly in favor of the existence of a link between PM and VTE. Notably, following our systematic review, other clinical studies have been published in the last few months, all documenting such an association. For instance, an adverse effect of higher concentrations of ambient air pollution on pulmonary embolism (PE) epidemiology was reported in the frame of a case-crossover study conducted in Spain from 2001 to 2013 and recently published in this Journal [ ]. In addition, another recent retrospective case–control study conducted in Italy documented that the short-term exposure to high levels of air pollution was associated with a 2.5-fold increase in the risk of unprovoked proximal deep vein thrombosis (DVT) [ ].