Vitamin K status and vascular calcification: evidence from observational and clinical studies.

Vascular calcification occurs when calcium accumulates in the intima (associated with atherosclerosis) and/or media layers of the vessel wall. Coronary artery calcification (CAC) reflects the calcium burden within the intima and media of the coronary arteries. In population-based studies, CAC independently predicts cardiovascular disease (CVD) and mortality. A preventive role for vitamin K in vascular calcification has been proposed based on its role in activating matrix Gla protein (MGP), a calcification inhibitor that is expressed in vascular tissue. Although animal and in vitro data support this role of vitamin K, overall data from human studies are inconsistent. The majority of population-based studies have relied on vitamin K intake to measure status. Phylloquinone is the primary dietary form of vitamin K and available supplementation trials, albeit limited, suggest phylloquinone supplementation is relevant to CAC. Yet observational studies have found higher dietary menaquinone, but not phylloquinone, to be associated with less calcification. Vascular calcification is highly prevalent in certain patient populations, especially in those with chronic kidney disease (CKD), and it is plausible vitamin K may contribute to reducing vascular calcification in patients at higher risk. Subclinical vitamin K deficiency has been reported in CKD patients, but studies linking vitamin K status to calcification outcomes in CKD are needed to clarify whether or not improving vitamin K status is associated with improved vascular health in CKD. This review summarizes the available evidence of vitamin K and vascular calcification in population-based studies and clinic-based studies, with a specific focus on CKD patients.