What Is Vitamin K2 and Why Does It Matter?
Vitamin K is a fat-soluble nutrient that comes in two primary forms: vitamin K1 and vitamin K2. While K1 is primarily found in leafy green vegetables like kale and spinach and is essential for blood clotting, vitamin K2 (or menaquinone) has a distinct and crucial role in regulating calcium metabolism. It helps direct calcium into bones and teeth while preventing its harmful accumulation in arteries and soft tissues. Given its importance for bone and cardiovascular health, identifying the best dietary sources is key for overall wellness.
Vitamin K2 can be further broken down into several subtypes, with menaquinone-4 (MK-4) and menaquinone-7 (MK-7) being the most well-studied. MK-4 is found predominantly in animal products, while MK-7 is a product of bacterial fermentation. Their different molecular structures affect how they are absorbed and used by the body, with MK-7 offering superior bioavailability and a longer half-life, meaning it stays active in the body for much longer than MK-4.
Fermented Foods: The Best Sources of MK-7
For the highest concentration of vitamin K2, specifically the highly bioavailable MK-7, fermented foods are the clear winner. The fermentation process, driven by specific bacteria, dramatically increases the menaquinone content.
Natto
Without a doubt, the top food source of vitamin K2 is natto, a traditional Japanese dish of fermented soybeans. Its unique preparation using the bacterium Bacillus subtilis results in exceptionally high levels of MK-7. While its strong, pungent flavor and sticky texture are an acquired taste for some, a small daily serving can provide a potent dose of K2.
Hard and Soft Cheeses
Certain types of cheese are excellent sources of vitamin K2, with content varying by type and aging process. The longer the cheese is aged, the higher the menaquinone levels tend to be. Cheeses from grass-fed animals generally contain more K2 than those from grain-fed animals.
- Gouda and Edam: These cheeses are consistently cited as being particularly high in menaquinones, especially MK-9.
- Brie and Munster: These soft cheeses also offer significant amounts of vitamin K2.
- Other hard cheeses: Aged cheddars and Swiss cheeses contribute to K2 intake.
Sauerkraut and Kefir
While not as rich as natto, other fermented foods also offer small amounts of vitamin K2. Sauerkraut, made from fermented cabbage, and kefir, a fermented milk drink, are notable examples. These also provide beneficial probiotics that contribute to overall gut health.
Animal Products: Rich in MK-4
Animal products are the primary source of MK-4, a form of vitamin K2 that is synthesized by animal tissues. For optimal K2 intake from these sources, it is recommended to consume products from pasture-raised or grass-fed animals, as their diet results in higher vitamin content.
Organ Meats
Organ meats are some of the richest animal-based sources of vitamin K2, particularly the liver. Goose liver pâté and chicken liver are especially notable for their high MK-4 concentrations.
Eggs
Egg yolks, particularly from pasture-raised chickens, contain meaningful amounts of MK-4. The higher vitamin content in these eggs compared to those from caged hens is a direct result of the animals' diet.
Meat and Butter
While in lower concentrations than liver, meat and butter from grass-fed animals also provide vitamin K2. Good options include chicken (especially dark meat), goose, and grass-fed butter or ghee.
MK-4 vs. MK-7: A Comparison
To highlight the differences between the two main forms of vitamin K2, here is a comparison table:
| Feature | Menaquinone-4 (MK-4) | Menaquinone-7 (MK-7) |
|---|---|---|
| Primary Sources | Animal products (organ meats, egg yolks, pasture-raised butter) | Fermented foods (natto, certain cheeses, sauerkraut) |
| Half-Life | Short (clears from bloodstream in 6-8 hours) | Long (remains in bloodstream for several days) |
| Bioavailability | Lower; requires larger, more frequent doses for therapeutic effects | Higher; smaller, once-daily doses can be effective |
| Primary Function | Acts on vitamin K-dependent proteins, especially in the liver | Offers prolonged activity for extra-hepatic tissues like bones and arteries |
For Vegetarians and Vegans
Acquiring vitamin K2 can be more challenging on a vegetarian or vegan diet, as most rich sources are animal-based. Natto is the primary and most potent vegan option for MK-7, though its taste is not universally loved. Some fermented products like sauerkraut and tempeh also provide some K2, though in much lower quantities. Gut bacteria can convert some K1 into K2, but this process is not efficient enough for most people to rely on, making supplementation an important consideration for vegans.
Conclusion
Understanding which foods contain high vitamin K2 is essential for anyone looking to support their bone and heart health. For a powerful and readily available source of the highly bioavailable MK-7, natto is unparalleled. For those who prefer more Westernized options, a diet incorporating grass-fed dairy products, organ meats, and eggs can provide a steady supply of MK-4. By strategically incorporating these foods, individuals can ensure they are receiving adequate levels of this often-overlooked but incredibly important fat-soluble vitamin. For more information on vitamins and healthy eating, you can visit the Cleveland Clinic Health Essentials blog.
Foods with High Vitamin K2: A Summary
Here is a quick reference of foods containing high vitamin K2:
- Natto: The richest source of MK-7, from fermented soybeans.
- Goose Liver Pâté: An exceptionally high source of MK-4.
- Hard Cheeses: Gouda and aged cheddar offer good amounts of K2.
- Chicken and Egg Yolks: Especially from pasture-raised sources, rich in MK-4.
- Grass-Fed Butter: Contains significant MK-4.
- Sauerkraut and Kefir: Provide smaller, but still beneficial, amounts of K2 from fermentation.
Final Thoughts on Intake
Balancing MK-4 from animal sources and MK-7 from fermented foods can provide comprehensive K2 coverage. For those with dietary restrictions or who find K2-rich foods unpalatable, a high-quality supplement may be a beneficial option after consulting a healthcare professional.
Key Takeaways
- Natto is the richest source of vitamin K2 (MK-7), offering an exceptionally high concentration from fermented soybeans.
- Animal products, especially organ meats like goose or chicken liver, contain significant levels of vitamin K2 in the MK-4 form.
- Certain cheeses, notably Gouda and Brie, are good dairy sources of K2, with levels increasing as the cheese ages.
- MK-7 is more bioavailable and has a longer half-life than MK-4, making it more efficient for the body to use.
- Vegans face challenges in obtaining K2, relying mainly on natto and potentially other fermented foods, making supplementation a consideration.
- Sourcing matters for animal products; grass-fed and pasture-raised options contain higher K2 levels.
FAQs
Q: Is vitamin K1 the same as vitamin K2? A: No, they are different forms of vitamin K. Vitamin K1 (phylloquinone) is found in leafy greens and is primarily used for blood clotting, while vitamin K2 (menaquinone) is found in animal and fermented foods and is crucial for regulating calcium.
Q: What is the difference between MK-4 and MK-7? A: MK-4 is a short-chain menaquinone found in animal products, while MK-7 is a long-chain menaquinone produced by bacteria in fermented foods. MK-7 has a longer half-life and is more bioavailable.
Q: Why is natto so high in vitamin K2? A: Natto's high vitamin K2 content is due to the specific bacteria (Bacillus subtilis) used in its fermentation process, which produces large amounts of the MK-7 subtype.
Q: Can vegans get enough vitamin K2 from their diet? A: It can be challenging. Natto is the best vegan source, but other fermented foods like sauerkraut and tempeh provide much lower amounts. Gut bacteria can produce some K2, but this is often not sufficient, so supplementation may be necessary.
Q: Do all cheeses have the same amount of vitamin K2? A: No, the vitamin K2 content varies significantly by the type of cheese, the bacterial cultures used, and the aging process. Hard, aged cheeses like Gouda and certain soft cheeses like Brie tend to be higher in K2 than others.
Q: Does cooking affect the vitamin K2 content in foods? A: Vitamin K2 is fat-soluble and relatively stable under typical cooking temperatures. However, excessive or prolonged heat may degrade some nutrients. The preparation method is more critical, particularly for fermented products.
Q: Should I be worried about vitamin K2 and blood thinners? A: Yes, individuals on anticoagulant medication like warfarin should consult a physician before significantly altering their vitamin K intake, including K2, as it can affect medication effectiveness.
Q: Is it necessary to supplement with K2? A: While food sources are ideal, supplementation can be beneficial, especially for individuals who do not consume animal or fermented products, or those with dietary malabsorption issues. Consult a healthcare provider to determine if supplementation is right for you.
Citations
Richest Food Sources of Vitamin K2 - Dr Steven Lin. (n.d.). Dr Steven Lin. Top Foods High in Vitamin K2 - WebMD. (2024, October 18). WebMD. Top Foods High in Vitamin K2 - WebMD. (2024, October 18). WebMD. Vit K2 for heart and bone health - why is it important? - OstroVit. (2025, October 3). OstroVit. Health Benefits of Vitamin K2 for Bones and Heart Wellness. (2025, September 30). InstaCare.
