What does vitamin K do to the body? An essential guide to its core functions

January 3, 2026 •

3 min read

Over 70% of older women in the U.S. may take calcium supplements, yet many are unaware that vitamin K is crucial for directing that calcium to the bones and preventing arterial calcification. This guide explores exactly what does vitamin K do to the body, revealing its profound impact on your health beyond simple blood clotting.

Quick Summary

Vitamin K is a fat-soluble nutrient essential for activating proteins involved in several key physiological processes. It is vital for blood clotting, bone mineralization, and preventing soft tissue calcification in arteries. Proper intake supports bone density, cardiovascular health, and overall well-being by regulating calcium and other important functions.

Key Points

Essential for Blood Clotting: Vitamin K activates proteins in the liver (clotting factors II, VII, IX, X) that are necessary for proper blood coagulation and wound healing.
Supports Bone Health: It activates osteocalcin, a protein that binds calcium to the bone matrix, which is vital for building and maintaining strong bones.
Protects Cardiovascular System: Vitamin K activates Matrix Gla Protein (MGP), an inhibitor of arterial calcification that helps keep blood vessels flexible and healthy.
Works Synergistically with Vitamin D: It partners with vitamin D to ensure calcium is deposited in the bones and not in the arteries.
Two Important Forms: Vitamin K1 (from plants) mainly supports liver functions like clotting, while K2 (from fermented and animal foods) primarily benefits bone and cardiovascular health.
Dietary Consistency is Key on Warfarin: Patients on anticoagulants like warfarin must maintain a consistent intake of vitamin K to avoid dangerous interactions.

The Primary Functions of Vitamin K

Vitamin K is a family of fat-soluble vitamins, primarily known for two compounds: vitamin K1 (phylloquinone), found in plant foods, and vitamin K2 (menaquinones), found in animal products and fermented foods. The main function of vitamin K is acting as a cofactor for an enzyme that modifies proteins, allowing them to bind to calcium.

Vitamin K's Crucial Role in Blood Clotting

Vitamin K is vital for blood coagulation. It is necessary for synthesizing specific clotting factors (II, VII, IX, and X) in the liver. This process is critical for stopping bleeding and wound healing.

Protein Activation: Vitamin K activates prothrombin (Factor II) and other clotting factors through gamma-carboxylation.
Prevents Bleeding: Deficiency impairs this, increasing bruising and hemorrhaging risk.
Newborn Prophylaxis: Vitamin K injection at birth prevents potentially fatal bleeding in newborns.

Vitamin K and Bone Health

Vitamin K is essential for bone health by activating osteocalcin, a protein that helps bind calcium to the bone matrix for strength and mineralization. Low vitamin K levels result in inactive osteocalcin, potentially weakening bones.

Osteocalcin Activation: Vitamin K ensures functional osteocalcin for strong bones.
Reduces Fracture Risk: Studies suggest a link between higher vitamin K intake and lower fracture risk.
Synergy with Vitamin D: Vitamins D and K work together; D aids osteocalcin production, and K activates it.

Cardiovascular Health and Vitamin K

Vitamin K supports cardiovascular health by activating Matrix Gla Protein (MGP), which prevents calcium from accumulating in artery walls. Inactive MGP can lead to arterial stiffening and plaque buildup.

Prevents Calcification: Active MGP maintains artery flexibility by preventing calcium deposits.
Reduced Risk: Studies link higher K2 intake to a lower risk of coronary heart disease.
Long-Term Effect: K2 supports arterial health due to its longer half-life.

The Two Forms: Vitamin K1 vs. Vitamin K2

Vitamin K comes in two main forms with different sources and functions:


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Source	Green leafy vegetables (kale, spinach, broccoli), vegetable oils	Fermented foods (natto, certain cheeses), animal products (meat, eggs)
Main Function	Primarily involved in activating liver proteins for blood clotting	Extra-hepatic functions, notably bone health and inhibiting arterial calcification
Bioavailability	Lower bioavailability, quickly cleared by the liver to support clotting	Higher bioavailability, longer half-life, better for extra-hepatic tissues
Dietary Intake	Represents the majority of vitamin K intake in most Western diets	Less common in typical Western diets, but can be converted from K1 or produced by gut bacteria

Dietary Sources and Daily Requirements

Meeting vitamin K needs through diet is important:

Vitamin K1 (Phylloquinone): Found in green leafy vegetables like kale and spinach, and cruciferous vegetables such as broccoli.
Vitamin K2 (Menaquinones): Rich sources include natto, certain cheeses, egg yolks, and organ meats.

Adequate intake for adults is typically 90 mcg/day for women and 120 mcg/day for men, though optimal levels for bone and cardiovascular health may be higher.

The Synergistic Relationship with Vitamin D

Vitamin D and vitamin K work together on calcium metabolism. Vitamin D promotes production of vitamin K-dependent proteins like osteocalcin and MGP, while vitamin K activates them. Some research suggests high-dose vitamin D without adequate K might increase arterial calcification. Combined intake is often recommended.

Potential Risks of Deficiency and Interactions

Vitamin K deficiency is uncommon in healthy adults but can occur with malabsorption disorders or certain medications like long-term antibiotics. Symptoms include easy bruising and bleeding.

Vitamin K interacts significantly with warfarin, an anticoagulant. Warfarin blocks vitamin K recycling. Patients on warfarin need consistent vitamin K intake. Newer anticoagulants do not have this interaction.

Conclusion

Vitamin K is vital for blood clotting, bone strength, and preventing arterial calcification by activating key proteins. A balanced diet with both K1 and K2 sources is recommended. Individuals with certain conditions or on specific medications should consult a healthcare provider regarding vitamin K intake. Understanding what vitamin K does to the body highlights its importance for overall health.

For more detailed health information, consult the National Institutes of Health.

Frequently Asked Questions

The main difference is their primary function and source. Vitamin K1, from plants, is mainly used by the liver for blood clotting, while Vitamin K2, from fermented foods and animal products, has a longer half-life and primarily supports bone and cardiovascular health.

Excellent sources of vitamin K1 include leafy green vegetables such as kale, spinach, and broccoli. For vitamin K2, good sources are fermented foods like natto, certain cheeses, and egg yolks.

Yes, but with strict consistency and under a doctor's supervision. Anticoagulants like warfarin block vitamin K's function. Maintaining a consistent daily intake is crucial to ensure the medication's effectiveness is not altered.

Symptoms of deficiency can include easy bruising, bleeding gums, prolonged bleeding from cuts, blood in the urine or stool, and frequent nosebleeds. Severe deficiency can lead to internal bleeding.

Vitamins D and K work synergistically. Vitamin D enhances the production of vitamin K-dependent proteins (like osteocalcin), and vitamin K is then required to activate these proteins. This combined action ensures calcium is properly utilized in bones and managed in arteries.

No, a clinically significant vitamin K deficiency is rare in healthy adults. It is more common in newborns, or in adults with conditions like severe malnutrition or malabsorption disorders, or those on certain medications.

Yes. Research suggests that an adequate intake of vitamin K2, in particular, may help protect against arterial calcification and stiffness by activating Matrix Gla Protein (MGP), which helps remove calcium from arteries.