Vitamin K2 as MK-4: What It Is and Where It Comes From

Vitamin K is a family of related molecules, and MK-4 is the member of the K2 group that sits closest to how your own body works.

Vitamin K comes in two main natural groups. Vitamin K1 (phylloquinone) is found mostly in dark green leafy vegetables. Vitamin K2 (menaquinones) is a group of related forms named MK-4 through MK-10, according to a 2024 review^[3].

The same review says about 80% of worldwide vitamin K intake is K1. K2 makes up the smaller share.

MK-4 is one K2 form. MK-7 is another, and it is a major component of natto, a fermented soybean food.

Vitamin K is fat-soluble, meaning it travels with dietary fat. MedlinePlus^[4] says your body needs it to make clotting factors in the liver, and that some studies suggest it helps maintain strong bones in older adults.*

MK-4 is unusual because your body can build it. In 2010, a Japanese team reported in a Nature paper^[1] that an enzyme called UBIAD1 (a prenyltransferase, meaning an enzyme that attaches a fat-like tail to a molecule) is a human MK-4 biosynthetic enzyme.

How they tested it: Switching UBIAD1 down with siRNA (a lab tool that silences a gene) reduced conversion of labeled vitamin K into MK-4 in human cells. Making the enzyme in insect cells also produced MK-4.

Where it is found: MK-4 turns up in specific tissues of humans and rats, including the brain, kidney and pancreas. That pattern suggests these tissues may make MK-4 locally from the K1 that comes from plants.

The catch: This was cell and animal-tissue work. It shows how the conversion can happen, not how much any one person converts.

Animals make MK-4 from vitamin K1 too, so MK-4 in food comes from animal products. Other menaquinones are made by bacteria and sit mostly in fermented foods, a 2021 Australian food database^[2] reports.

That database measured 60 commercial foods and found MK-4 in 31 of them. Median values per 100 grams, in micrograms (mcg):

• Eggs: 32.6 mcg
• Ham: 28.8 mcg
• Chicken: 26.4 mcg
• Butter: about 24.7 mcg
• Brie, cheddar, parmesan: 9.3, 5.5 and 5.4 mcg

The same paper estimates that menaquinones make up about 10% of the vitamin K people eat, and that up to 40% of dietary menaquinone is MK-4.

The catch: These are Australian foods, and values vary by brand and by how the animals were fed. The butter figure is the least certain, because the paper's table lists a range that does not contain its median. Treat it as approximate.

For reference, our vitamin D3 + K2 spray has 55 mcg (2200 IU) of vitamin D3 and 100 mcg of vitamin K2 per 1 mL serving.

Vitamin K dissolves in fat, not water. That affects how much of it you absorb from a meal.

The 2024 review says K1 absorption from a pure spinach or broccoli meal is only 5 to 10%. It roughly doubles when fat is in the same meal, the review notes^[3].

This is why animal foods such as eggs and butter, which carry MK-4 together with their own fat, are a natural match for how this vitamin behaves. Oil is also a natural carrier for any fat-soluble vitamin.

The catch: The 5 to 10% figure is for K1 from vegetables, not for MK-4. It shows the general role of fat, not a measured MK-4 result.

Some proteins in your body cannot grab calcium until vitamin K activates them. Vitamin K acts as a helper (a cofactor) for an enzyme that adds chemical groups to the protein's building blocks. This process is called carboxylation, and it gives the protein its calcium-binding grip, the 2024 review explains^[3].

Two of these proteins matter most for calcium handling. Osteocalcin is made by bone-building cells and has three carboxylated glutamic acid units. Matrix Gla protein (MGP) works alongside it.

In this model, vitamin K helps these proteins direct calcium toward bone.* Researchers also use the ratio of activated to inactive osteocalcin as a marker of vitamin K status.

The review adds that MK-4 and MK-7 were reported to be more effective than K1 at promoting bone-building cell activity in lab studies.* These were not head-to-head comparisons of MK-4 against MK-7 in people.

Vitamin D helps your body absorb calcium from food.* Vitamin K2 helps the proteins that handle that calcium afterward.* That is the logic behind pairing them, and it is covered in more depth in our K2 and D3 guide.

What studies pooled: A 2020 meta-analysis of eight randomized trials with 971 participants reported that vitamin K combined with vitamin D3 raised total bone mineral density, as summarized in the 2024 review^[3].

What the review concludes: Adequate vitamin K on top of good vitamin D status seems to add to the benefit for bone health.*

The catch: The review calls the evidence limited but suggestive.

One trial of 108 women, who already took a bone drug, calcium and vitamin D, added 1 mg of K1 or 45 mg of MK-4 a day and found no extra effect on bone density. The review calls the 45 mg dose pharmacological rather than nutritional.

The takeaway: vitamin D brings calcium in, and K2 helps guide it. Taking the two as a pair follows from how they work in the body.* For D3 amounts, see our D3 guide.

Vitamin K affects blood clotting, so it interacts with warfarin (Coumadin), a blood thinner. MedlinePlus^[4] says sudden changes in vitamin K intake can alter the medication's effect, so people on warfarin should keep intake consistent and ask their provider about it.

MedlinePlus lists the Adequate Intake (the level assumed enough for most people) as 90 mcg a day for adult women and 120 mcg for adult men. The 2024 review also notes that some drugs, including statins and ezetimibe, may affect vitamin K status.

Check with your doctor first if you:

• Take blood thinners (anticoagulants) or any other medication
• Are pregnant or breastfeeding
• Are giving it to a child
• Have a health condition, including kidney problems

The MedlinePlus page lists Adequate Intake levels but does not state a tolerable upper limit. Amounts for these groups are a question for your doctor.