Which Vitamin K Causes Blood Clotting: K1 vs. K2

December 24, 2025 •

4 min read

In 1929, the discovery of a nutrient essential for blood coagulation earned it the letter 'K' from the German word for coagulation. All forms of this fat-soluble vitamin are necessary for proper blood clotting, but they each play different, specific roles. This article clarifies which vitamin K causes blood clotting and its role in maintaining a healthy body.

Quick Summary

All forms of vitamin K are vital for normal blood coagulation, but Vitamin K1 primarily influences the clotting factors produced in the liver. Both K1 and K2 are essential cofactors for the proteins required for effective clotting, preventing excessive bleeding. Deficiency impairs this process, leading to increased bleeding tendencies and other health issues.

Key Points

Vitamin K1 is the primary clottor: Phylloquinone (K1), found abundantly in green leafy vegetables, is the main form of vitamin K that the liver uses to produce blood clotting factors.
Vitamin K2 is also involved: Menaquinone (K2), made by gut bacteria and found in fermented foods, also supports coagulation but has broader benefits for bone and cardiovascular health.
Mechanism requires gamma-carboxylation: Both forms of vitamin K act as a co-factor for an enzyme that modifies specific proteins, allowing them to bind calcium and initiate the clotting cascade.
Deficiency causes impaired clotting: A lack of vitamin K leads to the production of inactive clotting proteins, resulting in an inability to form effective clots and causing excessive bleeding.
Consistency is key with warfarin: Individuals on the blood thinner warfarin must maintain a consistent intake of vitamin K, as fluctuations can interfere with the medication's effect.
Both forms are essential: While K1 focuses on liver-based coagulation, a balanced diet including both K1 and K2 is crucial for overall health.

The Core Mechanism of Vitamin K in Coagulation

Vitamin K is a family of compounds crucial for producing the proteins that enable blood clotting. Without it, the body cannot create specific vitamin K-dependent clotting factors, impairing coagulation and leading to excessive bleeding. Vitamin K acts as a co-enzyme for gamma-glutamyl carboxylase, an enzyme that modifies inactive clotting factors, specifically factors II (prothrombin), VII, IX, and X. This modification, called carboxylation, allows these proteins to bind calcium ions, which is essential for initiating the clotting cascade on activated platelets at the site of injury.

The Distinct Roles of Vitamin K1 and K2

Both vitamin K1 and K2 facilitate coagulation, but they differ in sources, absorption, and distribution. The body efficiently recycles vitamin K for liver needs.

Vitamin K1 (Phylloquinone)

Found primarily in green, leafy vegetables and plant oils, K1 is the most common form in the diet. It's mainly transported to the liver, where it drives the synthesis of coagulation factors, making it the principal dietary form for normal blood clotting functions in the liver.

Vitamin K2 (Menaquinone)

K2 refers to menaquinones, produced by gut bacteria or found in fermented foods and animal products. K2 circulates longer and distributes more broadly to extra-hepatic tissues like bones and blood vessel walls. While supporting coagulation, K2 is also vital for bone health and preventing arterial calcification. The idea that K2 causes excessive clotting is unfounded; it contributes to the vitamin K pool for balanced coagulation.

Comparison of Vitamin K1 and K2 for Blood Clotting


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Source	Leafy green vegetables (e.g., kale, spinach) and plant oils.	Fermented foods (e.g., natto), some cheeses, and animal products.
Absorption	Primarily absorbed in the small intestine, but absorption is less efficient.	Often better absorbed, especially when consumed with fat.
Distribution	Primarily targeted for use by the liver to produce clotting factors.	Distributed more broadly to extra-hepatic tissues like bones and arteries.
Primary Role in Coagulation	The principal dietary contributor to the liver's production of clotting factors.	Also supports coagulation but has a more pronounced effect on cardiovascular and bone health.

Potential Risks and Medication Interactions

Dietary vitamin K is generally safe for most healthy individuals. However, those on blood-thinners like warfarin must maintain consistent vitamin K intake. Warfarin blocks vitamin K recycling, preventing active clotting factor production. Fluctuations in intake can affect the medication's effectiveness. Consult a healthcare provider before changing diet or taking supplements if on these medications.

Conclusion

Both K1 and K2 contribute to blood clotting, but K1 from leafy greens is the main form used by the liver for coagulation factors. K2, from fermented and animal foods, also supports clotting but is more known for bone and cardiovascular benefits due to broader distribution and longer half-life. Therefore, both K1 and K2 cause blood clotting, with K1 being dominant for liver function. Consistent intake of both is vital for health.

The Role of Vitamin K in the Clotting Cascade

Blood coagulation is a complex cascade relying on protein activation to form a clot. Vitamin K is essential for this process:

Hepatic Synthesis: The liver creates precursor proteins for clotting factors II, VII, IX, and X.
Vitamin K-Dependent Modification: These precursors are inactive until modified by a vitamin K-dependent enzyme.
Gamma-Carboxylation: The enzyme performs gamma-carboxylation, adding a carboxyl group to specific amino acids.
Calcium Binding: Carboxylated factors bind calcium ions.
Assembly and Activation: Calcium binding allows factors to assemble on activated platelets at the injury site, accelerating the cascade to form fibrin, the clot's protein mesh.

Vitamin K enables the activation of proteins needed for the cascade. For more details on the mechanism, you can refer to the linked source The mechanism of action of vitamin K in the clotting cascade.

Conclusion: Which Vitamin K Causes Blood Clotting?

Both Vitamin K1 and K2 are crucial for blood clotting, with K1 primarily supporting the liver's coagulation needs and K2 offering broader systemic benefits. A balanced diet including sources of both is essential for proper clot formation, preventing excessive bleeding, and overall health.

Food Sources of Vitamin K1 and K2

Include these foods for sufficient intake:

Vitamin K1 Sources

Kale
Spinach
Collard greens
Turnip greens
Broccoli
Brussels sprouts
Cabbage
Vegetable oils

Vitamin K2 Sources

Natto (fermented soybeans)
Egg yolks
Certain cheeses
Beef liver
Chicken

Recommended Dietary Intake

A varied diet usually meets vitamin K needs for healthy adults. However, deficiency can occur in newborns or those with certain conditions. Adequate Intake (AI) recommendations from the NIH are:

Adult Males: 120 mcg per day
Adult Females: 90 mcg per day
Pregnant or Lactating Females: 90 mcg per day

Consult a healthcare provider for specific needs, especially with health conditions or medication affecting vitamin K absorption.

Frequently Asked Questions

Vitamin K1 (phylloquinone) is mainly found in leafy green vegetables and is primarily used by the liver for blood clotting. Vitamin K2 (menaquinone) is produced by gut bacteria and is found in fermented and animal foods, with broader health benefits for bones and heart health.

For healthy individuals, consuming normal dietary amounts of vitamin K does not cause excessive clotting. The body regulates the process carefully. However, individuals on blood-thinning medication like warfarin must be careful with their intake.

Vitamin K is a necessary co-factor for the synthesis and activation of several key coagulation factors, including factors II (prothrombin), VII, IX, and X.

The primary symptom of vitamin K deficiency is excessive bleeding. This can manifest as easy bruising, blood under the nails, nosebleeds, blood in the stool, or internal bleeding.

Warfarin works by blocking the enzyme responsible for recycling vitamin K in the body. This prevents the activation of clotting factors, which is why a consistent vitamin K intake is critical for patients on this medication.

Vitamin K deficiency is rare in healthy adults because the vitamin is widely available in food and produced by gut bacteria. It is more common in newborns, individuals with malabsorption disorders, liver disease, or those on certain medications.

Yes, most healthy individuals can obtain adequate vitamin K from a balanced diet rich in leafy greens for K1 and fermented foods and some animal products for K2.