Vitamin K1
Phylloquinone (Vitamin K1)
Vitamin K1 (phylloquinone) is the plant-derived form of vitamin K, found naturally in leafy green vegetables and widely used as a dietary supplement to support blood coagulation and bone metabolism. It serves as an essential cofactor for the carboxylation of clotting factors II, VII, IX, and X, making it critical for hemostasis. Clinically, it is also used to reverse anticoagulant overdose and treat vitamin K deficiency bleeding in neonates.
Mechanism of Action
Vitamin K1 acts as a cofactor for the enzyme gamma-glutamyl carboxylase, which catalyzes the carboxylation of glutamic acid residues on vitamin K-dependent proteins, enabling them to bind calcium ions and become functionally active. This process is essential for the activation of coagulation factors and anticoagulant proteins C and S, as well as osteocalcin and matrix Gla protein involved in bone and vascular health. The vitamin K epoxide reductase complex (VKORC1) recycles vitamin K1 after carboxylation, a pathway inhibited by warfarin-class anticoagulants.
Evidence by Health Goal(17 goals)
Dosing Protocols
With a fat-containing meal to enhance absorption
Dietary reference intake for adults is 90-120mcg/day; supplement doses of 100-500mcg are commonly used. Absorption is significantly improved when taken with dietary fat. Doses up to 1000mcg are used in clinical settings for deficiency correction.
As prescribed; used in clinical or emergency settings
Intramuscular or subcutaneous injection used for warfarin reversal or severe deficiency. IV administration is reserved for life-threatening hemorrhage due to rare risk of anaphylactoid reactions and must be given slowly. Not a self-administration route outside of clinical supervision.
Safety & Side Effects
Vitamin K1 has an excellent safety profile at dietary and standard supplemental doses, with no established tolerable upper intake level set by most regulatory agencies due to low toxicity. However, it significantly interacts with warfarin and related anticoagulants, and patients on such medications must maintain consistent intake and consult their physician before supplementing.
Possible Side Effects
- !Generally very well tolerated at physiological supplemental doses
- !Gastrointestinal discomfort including nausea at high doses
- !Rarely, skin irritation or rash with topical or injection formulations
- !Anaphylactoid reaction with rapid intravenous administration (rare, clinical setting only)
- !Transient flushing or hypotension with IV injection if given too quickly
- !Potential reversal of anticoagulant therapy effect when used concurrently with warfarin
Interactions
- -Antagonizes warfarin (and other vitamin K antagonists) - even modest supplementation can reduce anticoagulant efficacy and alter INR; stable intake is critical for patients on anticoagulation therapy
- -Bile acid sequestrants (cholestyramine, colestipol) reduce absorption of fat-soluble vitamin K1 by up to 50%
- -Mineral oil and orlistat impair fat-soluble vitamin absorption, potentially reducing K1 bioavailability
- -Broad-spectrum antibiotics may reduce gut bacterial menaquinone synthesis, potentially increasing K1 requirements
- -Synergistic with vitamin D and calcium supplementation for bone health outcomes - commonly co-administered in osteoporosis protocols
Cost & Where to Buy
Vitamin K1 supplements are widely available OTC at low cost; pricing varies by dose, brand, and whether formulated alone or in combination products such as K1+K2 or multivitamins.
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