Vitamin K1 vs K2: What's the Difference?
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
K1 is the blood-clotting form, found in leafy greens and making up most dietary vitamin K. K2 is the one associated with directing calcium into bone rather than arteries. Both matter, and both antagonise warfarin — which is the single most important practical point.
Key takeaways
- K1 comes from leafy greens; K2 from fermented foods and animal products.
- MK-7 lasts days in the blood; MK-4 lasts hours, so dosing differs completely.
- Both interact directly with warfarin — tell your anticoagulation clinic before starting either.
K1 — clotting and greens
Phylloquinone makes up roughly 90% of dietary vitamin K, from kale, spinach, broccoli and other leafy greens. It is taken up mainly by the liver, where it activates the clotting factors. Deficiency is rare in people eating normally. This is the form that makes warfarin dosing sensitive to how many greens you eat.
K2 — calcium direction
Menaquinones come from fermented foods (natto is the richest source), some cheeses, and animal products, and gut bacteria produce some. K2 is distributed more widely to bone and vascular tissue than K1. Its role is carboxylating osteocalcin, which binds calcium into bone matrix, and matrix Gla protein, which inhibits arterial calcification.
MK-4 versus MK-7
These are not interchangeable. MK-7 has a half-life of around three days, so 90–180 mcg once daily works and it has randomised bone density data behind it. MK-4 clears in a couple of hours, so the Japanese trials used 45 mg — a dose 250 times larger — split through the day. A product listing a small MK-4 dose once daily is not replicating any trial.
Key ingredients to understand
The ingredients most relevant to this question, with what the evidence actually supports:
- Vitamin K2 MK-7 — MK-7 is the long-chain form of vitamin K2 with a half-life measured in days rather than hours, making once-daily dosing practical. It has…
- Vitamin K2 — Vitamin K2 is a fat-soluble vitamin that helps the body direct calcium toward bone and away from artery walls. The clearest research is on…
- Vitamin D3 (Cholecalciferol) — Vitamin D3 is the form your skin makes from sunlight and the form that raises and maintains blood levels most effectively. Deficiency is…
- Calcium — Calcium is the main mineral in bones and teeth and is essential for muscle and nerve function. Getting enough matters for bone health, but very…
Frequently asked questions
Do I need to supplement K1?
Rarely. Leafy greens supply plenty and deficiency is uncommon. K2 is the one with the supplemental rationale.
Can I take K2 on warfarin?
Not without telling your anticoagulation clinic. Vitamin K directly opposes warfarin and can push your INR out of range. This is a genuine safety issue.
Is D3 with K2 worth it?
The rationale — D3 raises calcium absorption, K2 directs where it goes — is coherent. Outcome evidence that the combination beats D3 alone is limited.
Related on FactoWiki
- All health answers
- Ingredient evidence guides
- Vitamin K2 MK-7 — ingredient guide
- Vitamin K2 — ingredient guide
- How we review
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