Vitamin K2: What the Fact Sheet Actually Separates from K1
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HEALTH BRIEFING
What the NIH fact sheet separates, and what it refuses to rank
Vitamin K2: what the fact sheet actually separates from K1
K1 is the dietary form. K2 is a family. The adult target is an Adequate Intake, not an RDA, and it does not name a winner.
Wild Foods Editorial Team · Updated October 13, 2026 · Sources checked October 13, 2026
Search "vitamin K2" and the first pages already know which form you should buy. The NIH Office of Dietary Supplements page does not. It splits the family into phylloquinone and a run of menaquinones, gives adults an Adequate Intake because the data were too thin for an RDA, and then stops.
That refusal to rank is the useful part.
"Phylloquinone is present primarily in green leafy vegetables and is the main dietary form of vitamin K."
NIH Office of Dietary Supplements, vitamin K fact sheet
"MK-4, MK-7, and MK-9 are the most well-studied menaquinones."
Same page. Studied is not the same as recommended.
"One study found that both phytonadione and MK-7 supplements are well absorbed, but MK-7 has a longer half-life."
Schurgers and colleagues, 2007, as cited by the fact sheet
What the labels collapse into one word
Vitamin K is a family with a shared chemical core, 2-methyl-1,4-naphthoquinone. Phylloquinone is vitamin K1. Menaquinones are vitamin K2, tagged MK-4 through MK-13 by the length of a side chain.
| Name on the label | What the fact sheet says it is | Where it mostly comes from |
|---|---|---|
| Vitamin K1 | Phylloquinone | Green leafy vegetables. The main dietary form. |
| Vitamin K2 | Menaquinones, MK-4 to MK-13 | Mostly bacterial. Modest amounts in some animal foods and fermented foods. |
| MK-7 | One menaquinone, not the whole family | A supplement form with a longer half-life than phytonadione in one study. |
Why there is no RDA
The Food and Nutrition Board did not have enough data to set an Estimated Average Requirement for vitamin K. So it set Adequate Intakes for every age, based on intakes in healthy groups. An AI is the level assumed to cover nutritional needs when an RDA cannot be built. It is a weaker number than an RDA, and the fact sheet does not pretend otherwise.
For adults 19 and older, the AI is 120 mcg a day for men and 90 mcg a day for women. Pregnancy and lactation stay at 90 mcg. The table does not split that target into K1 and K2. A bottle that implies the AI is an MK-7 quota is adding a sentence the board did not write.
What "longer half-life" does and does not mean
The fact sheet says limited data exist on how the supplement forms compare. It cites one study: both phytonadione, a synthetic K1, and MK-7 were well absorbed, and MK-7 had a longer half-life.
A longer half-life is a pharmacokinetic finding. It is not a bone outcome, and it is not a reason to ignore K1 from food. MK-4 can also be made in the body from phylloquinone, by a conversion that does not require gut bacteria. Long-chain menaquinones are a different story. They are largely bacterial.
THE DIET
K1 from greens
Still the main dietary form. The AI does not demote it.
THE FAMILY
MK-4, MK-7, MK-9
The three menaquinones the fact sheet calls the most studied. Not a ranking of products.
THE LIMIT
No upper level
The board set none, citing low toxicity. That is not a license for a 4,000 mcg capsule.
Deficiency is a clotting finding, not a marketing gap
The fact sheet says vitamin K deficiency is clinically relevant when prothrombin time rises because prothrombin activity in blood falls. Bleeding and hemorrhage are the classic signs, and they show up in severe cases.
Because vitamin K is required to carboxylate osteocalcin in bone, the same page says deficiency could also reduce bone mineralization. "Could" is the verb on the page. It is not a trial result for a capsule, and it is not a reason to self-check clotting time at home.
Where a product can sit
Supplements use K1 as phylloquinone or phytonadione, and K2 as MK-4 or MK-7. Most multivitamins include vitamin K at under 75 percent of the daily value. Single-nutrient products run wider, and some are very high. This article does not pick a dose.
Wild K2 and D3 is a Wild Foods product in that supplement category. Education-only means the name and the product page. No milligrams, no MK number, no test result in this article. Anyone on warfarin or a similar anticoagulant should talk with a clinician before changing vitamin K intake. The fact sheet calls that interaction serious.
A NARROW READ
K1 feeds the diet. K2 is a family. MK-7 lasts longer in one study. The AI does not crown a form.
If a page skips those four sentences, it is selling, not summarizing the fact sheet.
Related reading
- Magnesium deficiency: signs and what the RDA means
- What methylated vitamins actually change
- Wild K2 and D3 product page
Questions the fact sheet leaves open
Is MK-7 the same as vitamin K2?
It is one menaquinone inside vitamin K2. The family runs MK-4 through MK-13. MK-4, MK-7, and MK-9 are the most studied. A label that says only "K2" has not told you which one is in the bottle.
Why 120 mcg for men and 90 for women?
Those are Adequate Intakes for adults 19 and older, based on intakes in healthy groups. They are not RDAs, and they are not split by form.
Does no upper level mean any dose is fine?
The board set no upper level because adverse effects from food or supplements had not been reported in its review. The fact sheet still flags a serious interaction with warfarin and similar anticoagulants. Absence of an upper level is not a dosing instruction.
Can the body make K2 from K1?
It can make MK-4 from phylloquinone without gut bacteria. Long-chain menaquinones are largely bacterial in origin. Those are two different paths, and the fact sheet keeps them separate.
Sources
- Vitamin K — Health Professional Fact Sheet, NIH Office of Dietary Supplements. Updated March 29, 2021. Opened October 13, 2026. Cites Schurgers LJ, et al. Blood. 2007;109:3279-83.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
