Vitamin K1 (Phylloquinone)
Also known as: Phylloquinone, Phytonadione, K1
Phylloquinone is the primary dietary form of Vitamin K, underpinning its essential function in synthesizing biologically active coagulation factors (II, VII, IX, X) and anticoagulant proteins (C, S, Z). It serves as a cofactor for gamma-glutamyl carboxylase (GGCX), an enzyme vital for post-translational carboxylation of specific glutamic acid residues in these proteins. While directly involved in coagulation, its impact on bone mineralization and cardiovascular calcification appears less potent than menaquinones (Vitamin K2 forms), which have higher extrahepatic distribution.
Last reviewed: 2026-04-22 · 4 indexed studies
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Overview
Vitamin K1, or phylloquinone, is a fat-soluble vitamin primarily found in green leafy vegetables. Its most well-known function is its crucial role in blood coagulation, acting as a cofactor for the enzyme gamma-glutamyl carboxylase, which is essential for the activation of several clotting factors. Beyond coagulation, Vitamin K1 is also involved in bone metabolism and vascular health, although its role in these areas is less extensive compared to Vitamin K2 forms.
Mechanism & Function
Phylloquinone (K1) · C₃₁H₄₆O₂ — source: PubChem CID 5284607
Olive-green plant-derived vitamin K oil. Light-sensitive.
- Softgel
- Capsule
- Liquid
Softgel is generally preferred for bioavailability or efficacy.
Mechanism of Action
Vitamin K1 acts as a crucial cofactor for the enzyme gamma-glutamyl carboxylase (GGCX). GGCX catalyzes the post-translational carboxylation of specific glutamic acid residues on various proteins, including prothrombin and other coagulation factors (Factors VII, IX, X), as well as bone proteins like osteocalcin and matrix Gla protein (MGP). This carboxylation is essential for these proteins to bind calcium ions and become biologically active, enabling their roles in blood clotting and bone metabolism.
Physiological Role
Phylloquinone's primary physiological role is in hemostasis, where it is indispensable for the activation of coagulation factors in the liver. It facilitates the carboxylation of these zymogens, allowing them to bind calcium and participate in the coagulation cascade. Additionally, Vitamin K1 supports bone health by activating osteocalcin, though its contribution to extrahepatic carboxylation is generally perceived as less efficient than Vitamin K2 forms.
Primary Pathways
Performance / Health Relevance
While not directly enhancing athletic performance, adequate Vitamin K1 status is critical for overall health, particularly maintaining normal blood clotting, which is fundamental for recovery from injuries and preventing excessive bleeding. Its role in bone health is also relevant for athletes, contributing to skeletal integrity and reducing fracture risk, albeit less directly impactful than Vitamin K2.
Evidence Review
Compare Vitamin K Forms
Full comparison3 vitamin k forms are indexed. Bioavailability, clinical evidence, and best-use cases differ meaningfully between them.
| Form | Evidence |
|---|---|
Vitamin K1 (Phylloquinone)This page Fat-soluble vitamin; absorption is enhanced by dietary fat. Bioavailability from food sources, especially green leafy vegetables, can be variable due to entrapment within chloroplasts. | 65/100 |
| Vitamin K2 (MK-7) MK-7 has excellent bioavailability and a significantly longer half-life (approx. 72 hours) compared to K1 and other K2 forms, leading to more stable serum concentrations and sustained action. | 75/100 |
| Vitamin K2 (MK-4) MK-4 has a relatively short half-life compared to MK-7, requiring more frequent or higher dosing for sustained tissue levels. It is highly bioavailable when consumed with fat. | 70/100 |
Practical Use & Dosage
- Minimum Effective Dose
- 120 mcg/day (men); 90 mcg/day (women) [RDA]
- Optimal Range
- 90-120 mcg/day; up to 1-2 mg/day for specific conditions under medical supervision
- Upper / Caution Level
- No observed adverse effect level (NOAEL) established; generally very safe.
- Timing
- Can be taken with a meal containing fat to enhance absorption.
- Best Format
- Capsule, tablet, or part of a multivitamin; readily available in food.
- Bioavailability
- Fat-soluble vitamin; absorption is enhanced by dietary fat. Bioavailability from food sources, especially green leafy vegetables, can be variable due to entrapment within chloroplasts.
- Absorption Considerations
- Requires bile salts for absorption. Individuals with malabsorption disorders (e.g., cystic fibrosis, celiac disease, bariatric surgery patients) may have impaired absorption.
Safety & Interactions
Side Effects
- •Gastric upset (rare at therapeutic doses)
- •Allergic reactions (extremely rare, usually with IV forms)
Contraindications
- Individuals on anticoagulant therapy (e.g., warfarin)
Drug Interactions
- •Warfarin (major interaction, reduces anticoagulant effect)
- •Broad-spectrum antibiotics (can reduce gut flora production of K2, potentially impacting K1 indirectly)
- •Orlistat (can reduce absorption of fat-soluble vitamins, including K1)
- •Cholestyramine and colestipol (can bind to fat-soluble vitamins and impair absorption)
Who Should Avoid
- •Individuals on oral anticoagulant therapy (e.g., warfarin) without strict medical supervision.
- •Patients with severe liver disease (due to impaired metabolism and clotting factor synthesis, though K1 is still essential).
Monitoring
Patients on warfarin therapy require careful monitoring of INR (International Normalized Ratio) if Vitamin K1 intake changes significantly. For others, routine monitoring is not typically required unless malabsorption is suspected.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is Vitamin K1 (Phylloquinone) typically used or indicated?
Vitamin K1 (Phylloquinone) is most commonly used for: Blood clotting, Bone health. Phylloquinone's primary physiological role is in hemostasis, where it is indispensable for the activation of coagulation factors in the liver. It facilitates the carboxylation of these zymogens, allowing them to bind calcium and participate in the coagulation cascade. Additionally, Vitamin K1 supports bone health by activating osteocalcin, though its contribution to extrahepatic carboxylation is generally perceived as less efficient than Vitamin K2 forms.
How does Vitamin K1 (Phylloquinone) work?
Vitamin K1 acts as a crucial cofactor for the enzyme gamma-glutamyl carboxylase (GGCX). GGCX catalyzes the post-translational carboxylation of specific glutamic acid residues on various proteins, including prothrombin and other coagulation factors (Factors VII, IX, X), as well as bone proteins like osteocalcin and matrix Gla protein (MGP). This carboxylation is essential for these proteins to bind calcium ions and become biologically active, enabling their roles in blood clotting and bone metabolism.
What is the recommended dose of Vitamin K1 (Phylloquinone)?
The optimal range is 90-120 mcg/day; up to 1-2 mg/day for specific conditions under medical supervision. with a minimum effective dose of 120 mcg/day (men); 90 mcg/day (women) [RDA]. Best taken: Can be taken with a meal containing fat to enhance absorption.. Upper / caution level: No observed adverse effect level (NOAEL) established; generally very safe..
What are the side effects of Vitamin K1 (Phylloquinone)?
Reported side effects include: Gastric upset (rare at therapeutic doses); and Allergic reactions (extremely rare, usually with IV forms). Monitoring: Patients on warfarin therapy require careful monitoring of INR (International Normalized Ratio) if Vitamin K1 intake changes significantly. For others, routine monitoring is not typically required unless malabsorption is suspected.
Does Vitamin K1 (Phylloquinone) interact with medications?
Known or theoretical interactions: Warfarin (major interaction, reduces anticoagulant effect); Broad-spectrum antibiotics (can reduce gut flora production of K2, potentially impacting K1 indirectly); Orlistat (can reduce absorption of fat-soluble vitamins, including K1); and Cholestyramine and colestipol (can bind to fat-soluble vitamins and impair absorption). Always check with a clinician before combining with prescription medication.
Who should avoid Vitamin K1 (Phylloquinone)?
Vitamin K1 (Phylloquinone) is generally not recommended for: Individuals on oral anticoagulant therapy (e.g., warfarin) without strict medical supervision.; Patients with severe liver disease (due to impaired metabolism and clotting factor synthesis, though K1 is still essential).; and Individuals on anticoagulant therapy (e.g., warfarin).
How strong is the evidence for Vitamin K1 (Phylloquinone)?
Evidence level: Moderate (overall score 65/100), based on 4 indexed studies on SuppIndex.
Research & References (4)
Vitamin K and bone health in adult humans
This meta-analysis reviewed studies on vitamin K intake and bone health markers or fracture risk in adults. It concluded that while both K1 and K2 are involved in bone metabolism, the evidence for K2's benefit on bone mineral density and fracture risk is stronger and more consistent than for K1.
The vitamin K-dependent carboxylation pathway: advances in understanding and implications for human health
This review provides an in-depth look at the vitamin K cycle and the function of gamma-glutamyl carboxylase (GGCX), emphasizing the critical role of vitamin K as a cofactor for this enzyme in synthesizing active Gla-proteins, essential for coagulation and other physiological processes.
Determinants of vitamin K status in healthy adults
This study investigated dietary intake and circulating levels of vitamin K1 and K2 in healthy adults to identify factors influencing vitamin K status. It demonstrated that dietary intake of phylloquinone is the primary determinant of plasma K1 levels.
Interactions between warfarin and vitamins
This review systematically analyzed the interactions between warfarin and various vitamins, confirming that vitamin K (primarily K1) is the most significant interacting vitamin, as it directly antagonizes warfarin's anticoagulant effect.
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Research Overview
Moderate EvidenceCite this ingredient
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Stable URL
https://thesuppindex.com/ingredients/vitamin-k1-phylloquinone
SuppIndex. (2026). Vitamin K1 (Phylloquinone): Evidence summary, dosage and clinical studies. Retrieved October 23, 2026, from https://thesuppindex.com/ingredients/vitamin-k1-phylloquinone
Based on 4 indexed studies · Evidence level: Moderate.
Goal Ratings
Stack Compatibility
Generally safe with most supplements. Should be carefully managed with fat-soluble vitamins (A, D, E) to ensure balanced absorption, though direct interactions are rare. Magnesium and Calcium can be beneficial for bone health synergy.