What is Vitamin K1 (phylloquinone)?

Vitamin K1, also called phylloquinone or phytonadione, is a fat-soluble vitamin. It is essential for normal blood coagulation and supports bone-related protein activation.

What are the main benefits of Vitamin K1?

Vitamin K1 helps the body make clotting factors needed to prevent excessive bleeding. It also supports bone metabolism by activating proteins involved in bone mineralization.

What foods are high in Vitamin K1?

Vitamin K1 is found mainly in green leafy vegetables such as kale, spinach, and broccoli. It is also present in some vegetable oils.

How much Vitamin K1 should I take?

Typical supplemental amounts vary by individual needs; many products provide doses in the microgram range. If you use anticoagulants or have a medical condition affecting absorption, consult a clinician before supplementing.

Can Vitamin K1 interact with blood thinners like warfarin?

Yes. Vitamin K1 can affect the action of warfarin and related anticoagulants, so consistent intake and medical guidance are important when using these medications.

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Vitamin B

Vitamin B1 (Thiamine)

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Vitamin K1

Strong study situation·10/10

A higher score indicates better study conditions, but not necessarily effectiveness.

Vitamin K1 (phylloquinone) is a fat-soluble vitamin essential for blood clotting and bone health.

Cardiovascular Support Essential Nutrient Bone Health

dose range

90–1000 µg

Once daily with a meal containing fat

Consumption

Take with food to enhance absorption due to fat solubility.

Fat-soluble: take with fat.

Best time

Best taken with meals that contain fat (e.g., at breakfast or lunch).

Description

Vitamin K1, also known as phylloquinone or phytonadione, is primarily found in green leafy vegetables and is vital for normal blood coagulation and bone metabolism. Its supplementation is important in individuals with dietary deficiency or specific clinical needs.

benefits

Main effects with level of evidence

Strong

Note on evidence

Vitamin K1 is well established as essential for coagulation; its role in bone health is supported by moderate evidence, and there is limited evidence for cardiovascular protection.

Supports Normal Blood Clotting

Strong

Essential cofactor for the synthesis of key blood clotting factors (e.g., prothrombin); deficiency increases bleeding risk, and supplementation restores normal coagulation in those deficient.

Particularly relevant for: People with Vitamin K deficiency · Those on restricted diets · Individuals at risk of bleeding

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet 2 · American Journal of Clinical Nutrition (Vitamin K and coagulation)

Contributes to Bone Health

Moderate

Activates osteocalcin, a protein involved in bone mineralization; some studies report improvement in bone density and reduced fracture risk, particularly in postmenopausal women.

Particularly relevant for: Older adults · Postmenopausal women · Individuals at risk for osteoporosis

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet 3 · Osteoporosis International (Vitamin K and bone health meta-analysis)

May Support Cardiovascular Health

Limited

May help prevent arterial calcification by activating proteins that inhibit calcium buildup in blood vessels; higher intake is associated with lower risk of cardiovascular disease in observational studies.

Particularly relevant for: Older adults · Those at risk of cardiovascular disease

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet 4 · Journal of Nutrition (Vitamin K1 and cardiovascular health cohort study)

Safety & Information

Important safety information & known risks

For educational purposes only • not medical advice

Vitamin K1 is generally safe at dietary and supplemental levels, but high doses can interfere with certain medications or pose risks in rare conditions.

warning notices

Adverse reactions are rare with oral use; allergic reactions and injection site reactions are more likely with parenteral administration.
High doses can counteract the effects of anticoagulant drugs, increasing the risk of clotting.
Very high doses are contraindicated in those with hypersensitivity or rare clotting disorders.
Avoid use with warfarin or similar anticoagulants unless monitored by a physician, as Vitamin K1 can reduce their effectiveness.
Do not use if you have a known hypersensitivity to Vitamin K1 or related compounds.
Use with caution in individuals with clotting disorders without medical supervision.

Known interactions with medications

warfarin and other coumarin anticoagulants
some antibiotics

Contraindications / special precautions

Hypersensitivity to Vitamin K1 or excipients
Conditions with increased clotting risk without medical supervision

interactions

Important interactions between active ingredient ↔ supplement / medication / food

Vitamin K1 interacts primarily with anticoagulant medications and some antibiotics, potentially affecting drug effectiveness or Vitamin K status.

Vitamin K1 supplementation reduces the effectiveness of warfarin and similar anticoagulants.

drug · warfarin

MonitorStrong

Why

Vitamin K1 counteracts the anticoagulant effect of warfarin by promoting synthesis of clotting factors.

recommendation

Avoid high Vitamin K1 intake and monitor INR closely when using both; consult your healthcare provider.

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet 2 · American Journal of Clinical Nutrition (Vitamin K and coagulation)

Some antibiotics may decrease Vitamin K1 synthesis and absorption, increasing deficiency risk.

drug · broad-spectrum antibiotics

MonitorModerate

Why

Broad-spectrum antibiotics reduce Vitamin K-producing gut bacteria, lowering Vitamin K1 availability.

recommendation

Monitor for signs of bleeding or deficiency during prolonged antibiotic use.

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet

mechanisms of action

Brief explanations of how it works

Cofactor for Clotting Factor Synthesis

Vitamin K1 acts as a coenzyme for gamma-glutamyl carboxylase, needed for activation of clotting factors II, VII, IX, and X in the liver.

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet 2 · American Journal of Clinical Nutrition (Vitamin K and coagulation)

Activation of Osteocalcin for Bone Formation

Vitamin K1 carboxylates osteocalcin, enabling effective calcium binding and incorporation into bone matrix.

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet 3 · Osteoporosis International (Vitamin K and bone health meta-analysis)

Inhibition of Vascular Calcification

Activates matrix Gla protein, helping prevent pathological calcium deposition in arterial walls.

1 · NIH Office of Dietary Supplements – Vitamin K Fact Sheet 4 · Journal of Nutrition (Vitamin K1 and cardiovascular health cohort study)

Sources & References

Primary literature and reviews on which these statements are based

5 sources

NIH Office of Dietary Supplements – Vitamin K Fact Sheet

American Journal of Clinical Nutrition (Vitamin K and coagulation)

Osteoporosis International (Vitamin K and bone health meta-analysis)

Journal of Nutrition (Vitamin K1 and cardiovascular health cohort study)

WebMD – Vitamin K1

Last updated: February 13, 2026

This information is for educational purposes only and does not replace medical advice.