Vitamin K2
Also known as: Menaquinone, MK-7, MK-4, Menaquinone-7
The bone-and-artery vitamin that directs calcium where to go — the rising star paired with vitamin D.
In short
Vitamin K2 (menaquinone) is one of the two natural vitamin K families. While vitamin K1 (phylloquinone) handles blood clotting, K2 activates proteins that route calcium into bones and teeth — and out of arteries. This 'calcium traffic control' has made K2 one of the most studied bone-health supplements of the last decade, with MK-7 (from fermented foods like natto) favored for its long half-life. Evidence shows modest bone-density benefits, especially with vitamin D.
- Activates proteins that direct calcium into bone and out of arteries
- Main forms: MK-4 (short-acting) and MK-7 (long half-life, from natto)
- Strongest evidence: bone health alongside vitamin D
- CRITICAL interaction: counteracts warfarin (blood thinner)
What is Vitamin K2?
Vitamin K's classic job is blood clotting — every warfarin patient knows it. But a second family of K-dependent proteins, discovered more recently, does something different: they carboxylate (activate) osteocalcin, which binds calcium into bone, and matrix Gla protein, which keeps calcium out of artery walls. That dual action is the heart of K2's appeal: with vitamin D raising calcium absorption, K2 tells the calcium where to go. The evidence supports modest bone benefits; the artery story is promising but younger.
Where it comes from
Natural sources
- MK-7: natto (fermented soybeans) — by far the richest source
- MK-4: animal foods — liver, egg yolks, cheese, dark meat
- Some K2 is also made by gut bacteria
How it's made
Supplements use MK-7 from natto fermentation or synthetic MK-4, often in 45–200 mcg doses.
What it does in products
Benefits
Bone density (with vitamin D)
moderate evidenceTrials, especially with MK-4 (45 mg daily in Japanese studies) and MK-7 (100–180 mcg), show modest improvements in bone density and reduced fracture risk in some populations, particularly postmenopausal women.
Osteoporosis support
moderate evidenceK2 is a common adjunct in osteoporosis protocols alongside D3, with meta-analyses showing small but consistent vertebral fracture reductions in Asian populations (MK-4 trials).
Arterial calcification
emerging evidenceObservational studies link higher K2 intake with less arterial calcification and fewer cardiac events — promising, but large randomized trials are still underway.
The D3-K2 pairing
moderate evidenceHigh-dose vitamin D increases calcium absorption, and K2 helps direct it into bone — a mechanistically sensible combination popular in bone supplements.
Side effects & safety
Safety considerations
- Food-level K2 is safe in pregnancy; supplemental doses should be discussed with a provider.
- WARFARIN: any vitamin K reverses the anticoagulant effect — do not supplement K2 without medical management.
- May enhance the effect of calcium-raising therapies (vitamin D, thiazides) on bone — generally beneficial.
- Not for: Warfarin or other vitamin K antagonist therapy (unless medically managed)
How it's used
In supplements
Common protocols: MK-7 at 90–200 mcg daily, or MK-4 at 45 mg daily (Japanese osteoporosis dose). MK-7's half-life is days versus hours for MK-4, so MK-7 works as a once-daily supplement. Pair with vitamin D3 for the bone-directed calcium logic.
Regulatory status
- Dietary supplement under DSHEA; vitamin K is GRAS as a nutrient. In Japan, MK-4 is an approved osteoporosis treatment — the strongest regulatory validation K2 has received.
- GRAS (generally recognized as safe) for food use.
Popular products containing Vitamin K2
- Vitamin K2 MK-7 100 mcgNOW Foods · Supplement
- MK-7 Vitamin K2 — From nattoJarrow Formulas · Supplement
- Vitamin D3 + K2 — The classic pairingSports Research · Supplement
Product names and brands are shown for reference and belong to their respective owners.
MK-4 vs MK-7: the two K2s
K2 comes in a family of forms called menaquinones. MK-4 is found in animal foods and acts quickly — hence the 45 mg daily dosing in Japanese bone trials. MK-7 comes from natto and circulates for days, so 100–200 mcg daily suffices. Both activate the same proteins; MK-7's longer half-life makes it the practical daily choice, while MK-4 carries the largest trial base in Japan. Either is reasonable for bone goals.
Frequently asked questions
Should I take K2 with vitamin D3?
The pairing makes biological sense — D3 raises calcium absorption, K2 directs it into bone — and is supported by some trial evidence. Many bone formulas combine them; the standalone evidence for K2's bone benefit is strongest in populations with low baseline K2 intake.
Can vitamin K2 remove plaque from arteries?
No — that claim overpromises. K2 may slow calcification progression, but it does not remove existing arterial plaque, and randomized proof is still pending. The artery story is promising, not settled.
Who should not take vitamin K2?
Anyone on warfarin or similar anticoagulants — vitamin K directly reverses their effect. Anyone else at standard doses has little to worry about; K2 has no established toxicity.
The bottom line
Vitamin K2 is a sensible bone-health addition, especially paired with vitamin D3, with an intriguing (unproven) artery story. Choose MK-7 at 90–200 mcg daily or MK-4 at 45 mg, and treat warfarin as a hard stop sign.
References
- Vitamin K — Health Professional Fact Sheet. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
- Vitamin K2 and bone health — literature search. PubMed (National Library of Medicine). https://pubmed.ncbi.nlm.nih.gov/?term=vitamin+K2+bone+mineral+density+randomized
- Vitamin K2 and cardiovascular calcification — literature search. PubMed (National Library of Medicine). https://pubmed.ncbi.nlm.nih.gov/?term=menaquinone+arterial+calcification
- Menaquinone compound records. PubChem (National Library of Medicine). https://pubchem.ncbi.nlm.nih.gov/#query=menaquinone-7