Television viewing and venous thrombo-embolism: a systematic review and meta-analysis

Arterial thrombotic disease (atherosclerotic cardiovascular disease, CVD) and venous thrombo-embolism (VTE; comprising of deep vein thrombosis and pulmonary embolism) are two closely related diseases, which share common risk factors (obesity and smoking) and pathophysiological pathways (such as coagulation, platelet activation, and dyslipidaemia).1 Both disease states are associated with substantial morbidity, premature mortality, and high healthcare costs. It is well established that physical activity has an inverse and dose–response relationship with atherosclerotic CVD.2 Conversely, physical inactivity or prolonged sedentary behaviour is consistently associated with an increased risk of vascular diseases including atherosclerotic CVD.3 Though the evidence on the relationship between physical activity and VTE risk has mostly been inconsistent,4,5 a recent pooled analysis of 14 population-based prospective studies showed that regular physical activity was also associated with a reduced risk of VTE compared with physical inactivity.6 Physical activity and physical inactivity are not the same risk factor, but the evidence suggests that physical inactivity may also be associated with an increased risk of VTE. Television (TV) viewing is a major component of leisure sedentary time (physical inactivity) and there is documented evidence on its relationship with atherosclerotic CVD.7 Given the overall evidence, it is plausible that prolonged TV viewing may be associated with an increased VTE risk. However, the evidence so far has been inconsistent. Whereas some studies have reported an increased risk of VTE with prolonged TV viewing,8,9 others have reported no significant evidence of an association.10 Given the sparse and divergent evidence, there is a need for aggregation of the previous evidence, which will provide more power (in a larger sample of participants) to re-evaluate the association. In this context, using a systematic review and meta-analysis of all published observational cohort studies conducted on the topic, we sought to evaluate the nature and magnitude of the prospective association between TV viewing and VTE risk.