SummaryNaturally occurring forms of

Summary
Naturally occurring forms of vitamin K include phylloquinone (vitamin K1) and a family of molecules called menaquinones (MKs or vitamin K2). (More information)
With limited vitamin K storage capacity, the body recycles vitamin K in the vitamin K oxidation-reduction cycle in order to reuse it multiple times. (More information)
Vitamin K is the essential cofactor for the carboxylation of glutamic acid residues in many vitamin K-dependent proteins (VKDPs) that are involved in blood coagulation, bone metabolism, prevention of vessel mineralization, and regulation of various cellular functions. (More information)
Vitamin K deficiency increases the risk of excessive bleeding (hemorrhage). An injection of vitamin K is recommended to protect all newborns from life-threatening bleeding within the skull. (More information)
The adequate intake (AI) level for vitamin K is set at 90 μg/day for women and 120 μg/day for men. (More information)
Vitamin K deficiency may impair the activity of VKDPs and increase the risk of osteoporosis and fractures. Yet, observational studies have failed to isolate vitamin K intakes from overall healthful diets, thus warranting cautious interpretation of positive associations between vitamin K intakes and markers of bone health. Overall, intervention trials have been inconclusive regarding the role of supplemental vitamin K in further reducing bone loss in otherwise calcium- and vitamin D-replete adults. (More information)
Abnormal mineralization of blood vessels increases with age and is a major risk factor for cardiovascular disease. Vitamin K inadequacy may inactivate several VKDPs that inhibit the formation of calcium precipitates in vessels. The effect of supplemental vitamin K in the prevention of vessel calcification and cardiovascular events still needs to be evaluated in randomized controlled trials. (More information)
Phylloquinone is found at high concentrations in green leafy vegetables and certain plant oils, while most menaquinones are usually found in animal livers and fermented foods. (More information)
Several drugs, including vitamin K antagonists (e.g., warfarin), are known to interfere with vitamin K absorption and metabolism. (More information)