VK1

VK1, or vitamin K1, is also known as phylloquinone. It is a fat-soluble vitamin essential for blood coagulation and is principally found in green leafy vegetables and some vegetable oils.

Its function arises from a naphthoquinone ring with a long phytyl side chain; in the body, VK1 acts as a cofactor for gamma-glutamyl carboxylase, enabling carboxylation of glutamate residues on coagulation factors II, VII, IX, and X, which allows calcium binding in the clotting cascade. VK1 also participates in bone metabolism.

Absorption requires dietary fat and bile; after intestinal uptake it is transported in chylomicrons to the liver and then distributed via lipoproteins.

Common dietary sources include spinach, kale, broccoli, and other greens, as well as certain oils. In most adults, adequate intake is around 120 mcg/day for men and 90 mcg/day for women (values vary by region).

Deficiency is rare but can occur with malabsorption, liver disease, or prolonged antibiotic use; in newborns, vitamin K prophylaxis is standard to prevent hemorrhagic disease.

Interactions with anticoagulants such as warfarin require consistent VK1 intake to avoid INR fluctuations; high-dose VK1 supplements are not typically necessary and very large doses of the synthetic form menadione (VK3) can be harmful.

Origin: Vitamin K was discovered in the 1930s; VK1 is the plant form, distinct from VK2 (menaquinone) and VK3 (menadione).