Vitamin K2 is a group of nutrients, collectively called menaquinones, that help your body put calcium where it belongs: in your bones and teeth, not in your arteries. It’s one of two main forms of vitamin K. The other, vitamin K1, comes from green leafy vegetables and is best known for its role in blood clotting. Vitamin K2 plays a different and complementary role, primarily supporting bone strength and cardiovascular health.
How K2 Differs From K1
Vitamin K1 (phylloquinone) is made by plants. You get it from spinach, kale, broccoli, and similar vegetables. Vitamin K2 is produced by bacteria, both the kind living in your gut and the kind used to ferment foods like cheese, natto, and sauerkraut. While both forms contribute to blood clotting, K2 has a stronger connection to calcium regulation throughout the body.
Within the K2 family, there are actually several subtypes, labeled MK-4 through MK-13 based on their molecular structure. The two that matter most are MK-4, found in animal products like egg yolks and chicken, and MK-7, found in fermented foods. MK-7 stays active in your bloodstream longer than MK-4, which is why it’s the form most commonly used in supplements.
What K2 Does in Your Body
Vitamin K2 acts as a helper molecule for an enzyme that “switches on” certain proteins. Two of these proteins are especially important. The first, osteocalcin, works in your bones. Once activated by K2, osteocalcin binds calcium into the mineral matrix that makes bones hard and dense. Without enough K2, osteocalcin stays in an inactive form and can’t do this job effectively.
The second key protein is called Matrix Gla Protein, or MGP. This protein acts as a calcification inhibitor in your artery walls. When MGP is properly activated by K2, it prevents calcium from depositing in blood vessels. When vitamin K is deficient, inactive MGP accumulates, and that’s associated with increased cardiovascular risk. In short, K2 helps calcium go to bone and stay out of arteries.
K2 and Bone Health
Because K2 activates osteocalcin and promotes the binding of calcium into bone tissue, researchers have studied it extensively for osteoporosis prevention. The picture is mixed. Pharmacologic doses of MK-4 reduced fracture rates in some Japanese studies, and low-dose MK-7 showed site-specific effects on bone density in certain trials. But studies conducted outside Japan have often found no significant benefit for bone mineral density or fracture risk. K2 clearly plays a role in bone metabolism at a biochemical level, but whether supplements reliably prevent fractures for everyone remains an open question.
What’s better established is the partnership between K2 and vitamin D. Vitamin D increases calcium absorption from food, while K2 directs that calcium into bone. Animal studies show that vitamin K is most effective at building bone mass when vitamin D levels are adequate. Taking both together may be more effective for bone health than either one alone, and adding K2 may reduce the risk that high-dose vitamin D supplementation pushes excess calcium toward your arteries rather than your skeleton.
Cardiovascular Effects
The connection between K2 and heart health centers on arterial calcification, the buildup of calcium in blood vessel walls that contributes to stiffening and cardiovascular disease. By activating MGP, K2 helps keep arteries flexible. People with low vitamin K status tend to have higher levels of inactive MGP, which is associated with greater vascular calcification. This mechanism is well understood, though large-scale clinical trials proving that K2 supplements reduce heart attacks are still limited.
Best Food Sources of K2
Natto, a Japanese fermented soybean dish, is by far the richest source: one tablespoon contains about 150 micrograms. It has a strong, sticky texture that many people outside Japan find challenging, but nutritionally it’s unmatched for K2 content.
Cheese is a more accessible source, though amounts vary widely by type. A 50-gram serving of Munster provides roughly 50 micrograms, Camembert about 34, aged Gouda and Edam around 32, and cheddar only 12. Harder, aged, and bacterial-ripened cheeses tend to contain more K2 because the bacteria produce it during fermentation.
Other notable sources per 100-gram serving include:
- Eel: 63 micrograms
- Beef liver: 11 micrograms
- Chicken (dark meat): 10 micrograms
- Egg yolk: 67 to 192 micrograms per yolk, depending on what the hen was fed
- Sauerkraut: about 2.75 micrograms per half cup
- Butter: 2.1 micrograms per tablespoon
The wide range in egg yolks is notable. Pasture-raised hens eating insects and greens produce yolks with dramatically more K2 than conventionally raised hens.
How Much You Need
There is no official recommended daily intake specifically for vitamin K2. Government guidelines set an “adequate intake” for total vitamin K (K1 and K2 combined), and those values are based almost entirely on K1 data because food composition data for menaquinones is limited. The NIH has not established normal blood ranges for menaquinones either. Most supplement manufacturers use doses between 90 and 200 micrograms of MK-7 per day, but these numbers come from clinical studies rather than official dietary guidelines.
Signs of Deficiency
Because K1 and K2 overlap in some functions, deficiency in total vitamin K shows up as blood that takes longer to clot, easy bruising, and bleeding that won’t stop. Over time, low vitamin K status is also linked to weaker bones, including osteoporosis. A doctor can check your clotting function with blood tests if deficiency is suspected. Outright vitamin K deficiency is uncommon in adults who eat a varied diet, but subclinical insufficiency, enough K1 for clotting but not enough K2 for optimal bone and vascular health, may be more widespread.
K2 and Blood-Thinning Medications
If you take warfarin or a similar anticoagulant, vitamin K2 requires caution. Warfarin works by blocking vitamin K’s role in clot formation. A sudden increase in K2 intake, whether from food or supplements, can reduce warfarin’s effectiveness and raise the risk of dangerous clots. This doesn’t mean you need to avoid all vitamin K, but your intake should stay consistent from day to day so your medication dose stays properly calibrated. Any new supplement containing K2 should be discussed with whoever manages your anticoagulant therapy.