The risk of venous thromboembolism and physical activity level, especially high level: a systematic review.

Venous thromboembolism (VTE) is the third most common cause of cardiovascular disease. Connection between high level of physical activity (PA) and the onset of VTE is unknown. We searched the literature on the possible association between PA level, especially high levels, and the risk of VTE. A systematic review was carried out to identify relevant articles on the relation between PA level and VTE. The initial search was conducted together with the Karolinska Institutet University Library in February 2018, with follow-up searches after that. In total, 4383 records were found and then screened for exclusion of duplicates and articles outside the area of interest. In total, 16 articles with data on 3 or more levels of PA were included. Of these, 12 were cohort and 4 were case-control studies. Totally 13 studies aimed at investigating VTE cases primarily, while three studies had other primary outcomes. Of the 16 studies, five found a U-shaped association between PA level and VTE risk, although non-significant in three of them. Two articles described an association between a more intense physical activity and a higher risk of VTE, which was significant in one. Nine studies found associations between increasing PA levels and a decreasing VTE risk. Available literature provides diverging results as to the association between high levels of PA and the risk of venous thromboembolism, but with several studies showing an association. Further research is warranted to clarify the relationship between high level PA and VTE.