Vitamin K2
Fat-soluble vitamin that contributes to normal blood clotting and maintenance of normal bones.
Also known as Menaquinone, MK-7, MK-4, K2
Common doses
90-200 mcg
Best timing
Morning
Food
Take with food
Interactions
1 known
Vitamin K2 (menaquinone) is a fat-soluble vitamin that activates proteins responsible for directing calcium to the right places in the body. While Vitamin K1 (phylloquinone) is primarily involved in blood clotting, K2 has distinct roles in bone health and cardiovascular protection.
The key insight about K2 is its relationship with calcium and Vitamin D. Vitamin D increases calcium absorption, but K2 determines where that calcium goes. Without adequate K2, calcium may accumulate in arteries and soft tissues rather than bones. This is the 'calcium paradox': adequate calcium intake with insufficient K2 could theoretically worsen arterial calcification while failing to strengthen bones.
K2 exists in several sub-forms. MK-4 is found in animal products and has a short half-life (hours). MK-7 (from fermented foods like natto) has a much longer half-life (days), making it the preferred supplement form.
Key benefits
Calcium direction
K2 activates osteocalcin (which deposits calcium in bones) and matrix GLA protein (which prevents calcium from depositing in arteries).
Bone health
Vitamin K contributes to the maintenance of normal bones. K2 specifically activates osteocalcin, which is required for calcium incorporation into bone matrix.
Cardiovascular health
K2 activates matrix GLA protein, the most potent inhibitor of arterial calcification. The Rotterdam Study found K2 intake was inversely associated with aortic calcification.
Dental health
K2 activates osteocalcin in dental tissue, supporting the maintenance of healthy teeth.
Available forms
MK-7 (Menaquinone-7)
Preferred supplement form. Long half-life (72 hours). Derived from natto fermentation. 100-200 mcg daily is typical.
MK-4 (Menaquinone-4)
Found in animal products. Short half-life (6-8 hours). Requires higher doses or multiple daily doses. Used in some Japanese osteoporosis studies at 45 mg/day.
Food sources
- Natto (fermented soybeans, highest source)
- Hard cheeses (Gouda, Brie)
- Egg yolks (pastured)
- Liver (goose, chicken)
- Dark chicken meat
- Butter (grass-fed)
Signs of deficiency
- Easy bruising
- Poor bone density
- Arterial calcification
- Dental cavities despite good hygiene
- Slow wound healing
Upper intake limit
No established upper limit (NIH). K2 has no known toxicity even at high doses. Note: K2 should be avoided or used with medical supervision in people on warfarin or other vitamin K-dependent anticoagulants.
Research summary
Good evidence for bone health (especially MK-7 at 100-200 mcg). Promising evidence for cardiovascular protection from observational studies (Rotterdam Study, Prospect-EPIC). The D3+K2 pairing is well-supported mechanistically. K2 should not be confused with K1; they have different roles in the body.
Known interactions (1)
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This information is for educational purposes only. It is not medical advice and does not diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional.