Vitamin K: Functions, Mechanisms, Dosage, and Safety

Vitamin K: Functions, Mechanisms, Dosage, and Safety (Evidence-Based Guide)

Vitamin K is a fat-soluble vitamin essential for blood coagulation, bone metabolism, and vascular health. It exists in multiple forms with distinct physiological roles.

What is vitamin K?

Vitamin K includes:

Vitamin K1 (phylloquinone) → found in leafy greens
Vitamin K2 (menaquinones, MK-4, MK-7) → found in fermented foods and animal products

👉 K2 is more involved in calcium regulation outside the liver.

Mechanisms of action

Vitamin K functions as a cofactor for enzymes involved in:

Activation of clotting factors (II, VII, IX, X)
Activation of osteocalcin (bone protein)
Regulation of matrix Gla-protein (vascular calcification)

👉 These processes are essential for proper calcium distribution.

Evidence and clinical relevance

Blood coagulation

Vitamin K is essential for normal blood clotting. Deficiency increases bleeding risk.

Bone health

Vitamin K2 may support bone mineralization by activating osteocalcin.

👉 Evidence:

Moderate evidence for improved bone markers
Some studies suggest reduced fracture risk

Cardiovascular health

Vitamin K may help prevent arterial calcification.

👉 Evidence:

Observational data supports association
Clinical evidence is still evolving

Dietary sources

Leafy greens (K1): spinach, kale
Fermented foods (K2): natto, cheese
Animal products: eggs, liver

Dosage and intake

Recommended intake (AI):

Men: ~120 mcg/day
Women: ~90 mcg/day

Supplementation

Vitamin K1: general dietary support
Vitamin K2 (MK-7): 90–200 mcg/day commonly used

👉 Often combined with vitamin D for calcium metabolism.

Safety and side effects

Vitamin K is generally well tolerated.

👉 Side effects:

Rare at normal doses
High doses may interfere with anticoagulant therapy

Interactions

Anticoagulants (CRITICAL)

Warfarin and similar medications
Vitamin K reduces their effectiveness

👉 Requires strict medical supervision

Other interactions

Antibiotics (may reduce vitamin K production)
Fat malabsorption conditions

Deficiency

Rare but may occur in:

Fat malabsorption
Long-term antibiotic use
Newborns

👉 Symptoms:

Easy bruising
Bleeding

Limitations of supplementation

Benefits depend on baseline intake
Evidence stronger for deficiency correction than general use

Conclusion

Vitamin K plays a central role in coagulation, bone health, and calcium regulation. Supplementation may be beneficial in specific contexts, particularly when intake is insufficient or when combined with vitamin D.

Related guides:

Clinical Note

This content is for informational purposes only and does not constitute medical advice.

Nutritional supplements are not a substitute for professional medical evaluation. Consultation with a healthcare professional is recommended when using vitamin K alongside medications, especially anticoagulants.