The highest risk of cardiovascular events is in the morning, which may be associated with circadian changes in hemostasis. There is a 10% circadian variability in von Willebrand factor (vWF). Circadian periodicity has been noted for both the number of platelets and their aggregability. The highest number of platelets was in the afternoon, while most studies observed an increase in platelet aggregation in the morning. Platelet activity has also been linked with physical activity after waking up. The highest values of coagulation system markers such as fragment 1+2, factor VIIa, and fi - brinogen have been recorded in the late morning. Also, coagulation inhibitors such as protein C, antithrombin III, and a tissue factor pathway inhibitor are most active at this time of day. The levels of plasminogen and its activators (alpha 2-antiplasmin, urokinase-like plasminogen activator) do not undergo circadian periodicity, in contrast to changes in tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 levels (PAI-1). The most intensive activity of the fi brinolytic system inhibitor PAI-1 has been noted in the morning. The 24-h changes in the hemostatic system observed in healthy subjects often did not occur in individuals with health problems. The results of various studies suggest that circadian changes in the hemostatic system increase the incidence of cardiovascular events in the morning. This review considers the circadian rhythms of individual components involved in hemostasis (endothelium, platelets, coagulation, and fi brinolysis).

Keywords: Hemostasis, Blood Platelets, Circadian Rhythm