Vitamin K comprises a group of structurally similar fat soluble vitamins known as phylloquinone (vitamin K1) and menaquinone (vitamin K2). Vitamin K1 is synthesised by green plants and is highly biologically active in humans, while vitamin K2 is synthesised by bacteria. The human body requires vitamin K for the synthesis of specific proteins essential for blood coagulation and calcium binding in bone and other tissues.
Vitamin K, best known for it’s role in the formation of blood coagulant and anti-coagulant factors, also has important functions in protein synthesis and bone metabolism within the body. Research also indicates additional significance for vitamin K in the context of health and disease with reports suggesting a role in reducing the onset / effects of Alzheimers’ disease through it’s ability to inhibit oxidative stress-mediated nerve cell death. Furthermore, it has also been shown that vitamin K may have a role in reducing the onset of diabetes in the elderly.
Reference Intake (RI)
(Please note: RI values for vitamin K have not been published to date. The table below provides reccomended dietary reference values)
9 - 13
VITAMIN K (ug / kg / day)
VITAMIN K (ug / day)
(ug / 100g)
(ug / 100 g)
Deficiency / Toxicity
Impairments to lipid absorption, attributable to conditions such as coeliac disease, cystic fibrosis, or biliary obstruction, and the intake of specific therapies such as the anticoagulant Warfarin (a vitamin K antagonist), and the antibiotics, sulfonamides (inhibition of intestinal microbes), are all risk factors for the development of vitamin K deficiency. Neonates are also at risk of deficiency due to intestinal sterility and are thus administered prophylactic vitamin K at birth. Severe vitamin K deficiency results in impaired blood clotting, often manifest in uncontrolled internal bleeding. A deficiency in vitamin K may also result in weakened bones and the calcification of arteries and other soft tissues.
To date, there is no significant data to suggest that toxicity occurs if vitamin K is over-consumed. However, the isomer, vitamin K3, has been demonstrated as toxic when consumed in excess.