Vitamin K2
Menaquinone
The underappreciated partner to Vitamin D3, K2 activates proteins that direct calcium to bones and teeth while preventing dangerous arterial calcification.
What is Vitamin K2?
Vitamin K2 (menaquinone) is a fat-soluble vitamin that activates calcium-binding proteins responsible for directing calcium into bones and teeth while preventing its accumulation in arteries and soft tissues.
Known Health Benefits
How It Works
Vitamin K2 functions as an essential cofactor for the enzyme gamma-glutamyl carboxylase, which adds carboxyl groups to specific glutamic acid residues in vitamin K-dependent proteins (VKDPs), converting them from inactive to active forms. The two most important VKDPs for K2 are osteocalcin and matrix Gla protein (MGP). Osteocalcin, once carboxylated, binds calcium and integrates it into the hydroxyapatite crystal lattice of bone, promoting mineralization. Matrix Gla protein is the most potent known inhibitor of arterial calcification — when activated by K2, MGP binds calcium in arterial walls and prevents vascular calcification. This dual mechanism explains K2's unique ability to simultaneously support bone density and cardiovascular health. MK-7 (from natto fermentation) has a longer half-life (~72 hours) than MK-4 (~1–2 hours), providing stable 24-hour carboxylation of VKDPs at lower doses. MK-4 achieves higher tissue concentrations in specific organs including bone and brain. K2 does not affect clotting factors (K1's primary role) at physiological doses.
What Research Says
The Rotterdam Heart Study (Geleijnse et al., J Nutr 2004) followed 4807 subjects over 7 years and found that high dietary K2 intake (≥32 mcg/day) was associated with a 50% reduction in coronary heart disease mortality, 25% reduction in all-cause mortality, and 52% reduction in severe aortic calcification — K1 showed no such associations. A 3-year RCT by Knapen et al. (Thrombosis and Haemostasis, 2015) showed that 180 mcg/day MK-7 significantly improved arterial stiffness (carotid-femoral pulse wave velocity) and reversed age-related vascular stiffening in healthy postmenopausal women. For bone health, a Japanese RCT (Iwamoto et al., 2009) found MK-4 at 45 mg/day reduced fracture risk in postmenopausal women. A meta-analysis by Huang et al. (Osteoporosis International, 2015) confirmed that K2 supplementation significantly reduced fracture incidence. The K2 + D3 synergy is well-established: D3 upregulates osteocalcin and MGP production, while K2 activates them.
Active Compounds
MK-4, MK-7 (menaquinones)
Forms & Bioavailability
MK-7 has a much longer half-life (approximately 72 hours) compared to MK-4 (1–2 hours), allowing once-daily dosing at lower amounts. Both forms are fat-soluble and should be taken with a fat-containing meal for optimal absorption.
Dosage Guidance
| Use Case | Dosage |
|---|---|
| General health with D3 | 100–200 mcg MK-7/day |
| Cardiovascular protection | 180–360 mcg MK-7/day |
| Bone health (osteoporosis risk) | 200 mcg MK-7 or 45 mg MK-4/day |
Always consult a healthcare provider for personalized dosing.
Natural Food Sources
- Natto (Japanese fermented soybeans) — richest source
- Hard and aged cheeses (Gouda, Brie)
- Egg yolks (pasture-raised)
- Chicken liver and dark meat
- Butter (grass-fed)
- Sauerkraut
Potential Side Effects
Generally very safe; GI discomfort rare
Who Should Avoid It
- Warfarin or coumarin anticoagulant therapy (K2 antagonizes warfarin mechanism)
- Post-organ transplant on anticoagulants
- Known hypersensitivity to menaquinones
- Caution with novel oral anticoagulants (NOACs) — discuss with physician
Pregnancy & Lactation
Vitamin K2 is considered safe during pregnancy and lactation. Adequate K2 supports fetal bone development and may help prevent neonatal vitamin K deficiency. The typical supplement dose of 100–200 mcg MK-7 is not expected to interfere with neonatal vitamin K injection protocols.
Known Drug Interactions
MAJOR interaction with warfarin and other blood thinners — must monitor INR
Evidence Classification
Supported by cohort studies, case-control studies, or multiple observational studies with consistent findings.
Frequently Asked Questions
What is the difference between vitamin K1 and K2?
K1 (phylloquinone) is primarily involved in blood clotting and is abundant in green leafy vegetables. K2 (menaquinone) directs calcium to bones and away from arteries. K1 does not provide K2's cardiovascular or bone benefits. They are distinct vitamins with different roles despite sharing the 'vitamin K' name.
Should I take vitamin K2 with vitamin D?
Yes. Vitamin D increases calcium absorption and stimulates production of osteocalcin and matrix Gla protein. However, these proteins remain inactive without K2 to carboxylate them. Without K2, increased calcium absorption from D3 may contribute to arterial calcification rather than bone strength.
Is MK-7 better than MK-4?
MK-7 has a much longer half-life (72 hours vs 1–2 hours) and is effective at low doses (100–200 mcg). MK-4 requires much higher doses (15–45 mg) but achieves higher concentrations in specific tissues. MK-7 is more practical for daily supplementation; MK-4 is used in Japanese clinical protocols for osteoporosis.
Can I take vitamin K2 if I'm on blood thinners?
If you take warfarin, do NOT take K2 without physician supervision — it directly counteracts warfarin's mechanism. For newer anticoagulants (DOACs like rivaroxaban or apixaban), the interaction is less direct, but you should still consult your doctor before starting K2.
How much K2 do I need per day?
For general health alongside vitamin D3, 100–200 mcg MK-7 daily is well-supported. For cardiovascular protection, 180–360 mcg MK-7 is used in clinical studies. The Rotterdam Study associated intakes above 32 mcg/day with significant cardiovascular benefit.
References
- Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. Geleijnse JM, Vermeer C, Grobbee DE, et al.. Journal of Nutrition (2004)View study
- Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. Knapen MHJ, Braam LAJLM, Drummen NE, et al.. Thrombosis and Haemostasis (2015)View study
- Vitamin K2 supplementation and fracture incidence: a meta-analysis. Huang ZB, Wan SL, Lu YJ, et al.. Osteoporosis International (2015)
- A review of the role of vitamin K in bone and cardiovascular health. Maresz K. Integrative Medicine: A Clinician's Journal (2015)
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This entry is for educational purposes only. It is not medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement regimen, especially if you take medications or have health conditions.