Circadian variation within hemostasis: an underrecognized link between biology and disease?

Biological rhythms are a universal phenomenon in living organisms and serve to help organisms adapt within a circadian cycle to the 24-hour-oscillating environment. The rhythmic modulation of selective pathways thus enables organisms to optimize their ability to store and generate chemical energy, to minimize environmental stresses, and to reproduce by cycles of cell growth and division. Remarkably, the onset of both cardiovascular disorders and venous thromboembolism also undergoes circadian oscillations, which might be closely related to an internal biological clock. A highly repetitive rhythmic cycle seems to modulate platelet and endothelial functions, as well as the concentration and activity of several proteins of the coagulation and fibrinolytic systems. Although it is currently unknown how the global hemostatic efficiency might be affected by these circadian variations, understanding the nature, clinical significance, and pathophysiologic consequences of our hemostatic clock may be helpful for the prevention and treatment of a variety of conditions where either the severity of the illness or therapeutic efficacy exhibit circadian rhythmicity. In this review, clinical and laboratory data describing the effects of these cyclical rhythms on the hemostatic system are discussed.