You can get vitamin K2 from fermented foods, animal products, and supplements. The richest food source by far is natto, a Japanese fermented soybean dish, which contains 882 to 1,034 micrograms per 100 grams. Most Western diets are relatively low in K2 compared to K1 (the form abundant in leafy greens), so knowing where to find it and how to absorb it makes a real difference.
What Vitamin K2 Does in Your Body
Vitamin K2 activates a set of proteins that control where calcium goes in your body. Without enough K2, these proteins remain inactive, and calcium can end up in the wrong places.
In your bones, K2 activates a protein called osteocalcin. Once activated, osteocalcin binds calcium and helps deposit it into bone tissue, strengthening your skeleton. In your blood vessels, K2 activates a different protein (matrix Gla protein) that prevents calcium from accumulating in artery walls. So K2 essentially works as a traffic director: it pushes calcium toward bones and teeth while keeping it out of soft tissues where it causes harm.
This dual role is why K2 shows up in conversations about both bone density and heart health. Vitamin D3 increases how much calcium your body absorbs from food, but K2 is what ensures that calcium actually reaches your bones rather than settling in your arteries. Taking D3 without adequate K2 means more calcium in your bloodstream with less guidance on where it should go.
Best Fermented Food Sources
Fermented foods are the top dietary source of a long-lasting form of K2 called MK-7. Your body clears MK-7 more slowly than other forms, so it stays active in your bloodstream longer.
Natto dominates the category. At 882 to 1,034 micrograms per 100 grams, a single small serving exceeds any supplemental dose used in clinical research. The bacteria used to ferment natto (Bacillus subtilis) is the same species used to manufacture most MK-7 supplements commercially. If you can tolerate natto’s strong flavor and sticky texture, it’s the most efficient whole-food source available.
Hard cheeses like Gouda and Emmental contain some K2, but the concentrations are modest: roughly 1.1 to 1.5 micrograms per 100 grams. You’d need to eat an impractical amount of cheese to match even a low-dose supplement. Sauerkraut is even lower, at 0.1 to 0.3 micrograms per 100 grams. These foods contribute to your overall intake but shouldn’t be your primary strategy.
Animal-Based Sources
Animal products contain a different form of K2 called MK-4. Your body uses MK-4 quickly, so it doesn’t circulate as long as MK-7, but it’s still biologically active.
Organ meats are the standout. Goose liver contains around 370 micrograms per 100 grams, making it the richest animal source. Chicken liver and other organ meats also supply meaningful amounts, though less than goose liver. Conventional meat and egg products generally fall in the range of 2 to 22 micrograms per 100 grams, with egg yolks and dark meat poultry sitting toward the higher end of that range. These are useful additions to your diet but won’t cover your needs alone unless you eat organ meats regularly.
Grass-fed dairy products (butter, ghee, full-fat yogurt) are often cited as K2 sources, and they do contain MK-4, though precise concentrations vary with the animal’s diet. Pasture-raised animals that eat green plants convert vitamin K1 into MK-4 in their tissues, so the greener the feed, the more K2 ends up in the milk and fat.
What About Gut Bacteria?
Your gut bacteria do produce several forms of vitamin K2. Different species generate different forms: some produce MK-6, others MK-7, MK-8, or longer-chain versions like MK-10 and MK-11. However, how much of this bacterially produced K2 your body actually absorbs and uses remains unclear. Most of it is produced in the colon, where fat-soluble vitamin absorption is limited compared to the small intestine. Relying on gut production alone isn’t a reliable strategy for meeting your K2 needs.
K2 Supplements: MK-4 vs. MK-7
If your diet doesn’t include natto or organ meats regularly, supplements are the most practical option. The two forms you’ll find on shelves are MK-4 and MK-7, and they’re used at very different doses.
MK-7 is the more common supplement form. A three-year clinical trial in postmenopausal women found that 180 micrograms per day of MK-7 improved bone strength and slowed loss of vertebral height. Most MK-7 supplements on the market fall in the 100 to 200 microgram range, which aligns with this research.
MK-4 is used at far higher doses. In Japan, pharmacological doses of 45 milligrams per day (that’s 45,000 micrograms) are prescribed for osteoporosis treatment. Clinical trials have used either 15 or 45 milligrams daily. These doses are hundreds of times higher than MK-7 supplements because MK-4 is cleared from the body much faster. Over-the-counter MK-4 supplements in Western countries typically contain 1 to 5 milligrams, well below the therapeutic doses used in Japanese clinical practice.
No upper tolerable intake level has been established for any form of vitamin K2. Toxicity from K2 has not been documented even at high supplemental doses. That said, this doesn’t mean more is automatically better; it simply means the safety ceiling hasn’t been identified.
How to Absorb K2 Effectively
Vitamin K2 is fat-soluble, meaning your body needs dietary fat present in the gut to absorb it. Taking a K2 supplement on an empty stomach or with a fat-free meal significantly reduces how much you absorb. Pairing your supplement with a meal that includes butter, olive oil, avocado, nuts, or any other fat source helps ensure it gets into your bloodstream.
Many of the best food sources of K2 already come packaged with fat (egg yolks, cheese, liver, butter), so absorption from whole foods is generally not an issue. The concern is mainly relevant for people taking standalone supplements.
Pairing K2 With Vitamin D3
Vitamins D3 and K2 work as a functional pair. D3 increases calcium absorption from your digestive tract, and K2 directs that calcium into bone rather than letting it deposit in arteries and kidneys. Taking D3 supplements without adequate K2 raises the theoretical risk that excess absorbed calcium may contribute to soft tissue calcification over time, particularly at higher D3 doses.
This is why many supplements now combine D3 and K2 in a single capsule. If you’re already supplementing with vitamin D, adding K2 (or choosing a combination product) ensures the calcium pathway is fully supported.
Who Should Be Cautious
Vitamin K2 directly interferes with blood-thinning medications like warfarin. Warfarin works by blocking vitamin K’s activity, so taking supplemental K2 can reduce the drug’s effectiveness and increase clotting risk. If you take warfarin or a similar anticoagulant, you should not start K2 supplements without medical supervision. Even multivitamins and combination supplements may contain vitamin K, so checking labels is important. Anyone on these medications who does take K2 will need more frequent blood monitoring to keep their clotting time in the safe range.
Newer anticoagulants that don’t work through the vitamin K pathway generally don’t carry this interaction, but confirming with your prescriber is still worthwhile before adding any new supplement.