The life span of adults with end-stage renal disease is reduced, and cardiovascular disease (CVD) accounts for approximately half the deaths among those undergoing hemodialysis (HD). Vascular calcification is a key process in the development of atherosclerotic and arteriosclerotic CVD, and contributes significantly to the greater mortality rates and CVD events in HD patients. Recently, there has been growing interest in the vitamin K-dependent matrix Gla protein (MGP) and its role in inhibiting vascular calcification. Animal studies have revealed that the vitamin K-dependent protein MGP may reduce the progression of vascular calcification, possibly by means of improving vascular function. The relationship between MGP and vitamin K lies in the fact that inactive matrix Gla protein requires vitamin K to carboxylate it for its activation. Currently, data in HD patients are scant and equivocal on the effects of vitamin K supplementation on CVD risk outcomes. Therefore, the purpose of this 8-week randomized, placebo-controlled, double-blind clinical trial is to determine whether daily vitamin K supplementation can favorably alter measurements of endothelial function and arterial stiffness in HD patients.