phylloquinone

Phylloquinone, commonly called vitamin K1, is a fat-soluble vitamin that acts as a cofactor for the enzyme gamma-glutamyl carboxylase. This enzyme carboxylates specific glutamate residues in vitamin K–dependent proteins to form gamma-carboxyglutamate, enabling calcium binding. In humans, phylloquinone is essential for the gamma-carboxylation of coagulation factors II (prothrombin), VII, IX, and X, as well as the anticoagulant proteins C and S.

Dietary sources include green leafy vegetables such as spinach, kale, and broccoli, as well as some vegetable oils. Phylloquinone is absorbed with dietary fats in the small intestine, requiring bile for emulsification. After absorption it enters the lymphatic system as part of chylomicrons, is delivered to the liver, and then disseminated to tissues throughout the body.

In addition to its role in coagulation, phylloquinone supports bone metabolism and vascular health through gamma-carboxylation of specific bone-related proteins. The body stores phylloquinone in small amounts in the liver and adipose tissue, and it is continually recycled via the vitamin K cycle.

Intake guidelines vary by jurisdiction; in adults, an adequate intake is about 120 micrograms per day for men and 90 micrograms per day for women. Deficiency is rare but can occur with fat malabsorption, cholestasis, or long-term antibiotic use, leading to easy bruising and bleeding. High doses of phylloquinone are not associated with toxicity in healthy individuals.