Natto: The Unrivaled King of K2
For those seeking the absolute highest dietary concentration of vitamin K2, the answer is undeniably natto. A traditional Japanese dish made from fermented soybeans, natto contains an exceptionally high amount of menaquinone-7 (MK-7), a form of K2 with superior bioavailability and a longer half-life than other types. While its strong, pungent flavor and slimy texture can be an acquired taste, just one tablespoon can provide a significant dose of vitamin K2, along with gut-healthy probiotics. For vegetarians and vegans, natto is a unique plant-based option for this powerful nutrient, although finding it may require a trip to an Asian grocery store or a specialty health food shop.
Animal Products: Meat, Dairy, and Eggs
Outside of fermented foods, animal products are another key source of vitamin K2, particularly the MK-4 subtype. However, the K2 content in these products can vary significantly depending on the animal's diet. Grass-fed animals, for instance, produce higher concentrations of vitamin K2 in their meat and dairy compared to those fed grain or soy.
- Goose Liver Pâté: Among the richest animal sources, providing a significant amount of MK-4.
- Cheeses: Hard and soft cheeses, especially aged varieties like Gouda and Brie, contain moderate to high levels of MK-8 and MK-9. The longer the cheese is aged, the higher its K2 content tends to be.
- Egg Yolks: The yolk of eggs, particularly from pasture-raised chickens, offers a good source of MK-4. The K2 concentration is directly linked to the hen's diet.
- Chicken and Organ Meats: Chicken meat, especially the legs and thighs, is a decent source of MK-4. Organ meats like chicken or beef liver also contain notable amounts.
- Butter: High-fat dairy, such as butter from grass-fed cows, is another source of MK-4.
Other Fermented Foods
While natto is a standout, other fermented foods also offer smaller amounts of vitamin K2. Sauerkraut, made from fermented cabbage, is a more common Western-diet option, providing a modest but worthwhile amount of the nutrient. Kefir, a fermented milk drink, also contains some vitamin K2, alongside its probiotic benefits. The fermentation process allows beneficial bacteria to produce menaquinones, which we then consume.
Supplements: A Consistent and Convenient Alternative
For individuals with dietary restrictions or those who cannot stand the taste of natto, supplements are a reliable way to ensure adequate vitamin K2 intake. Most high-quality supplements use the MK-7 form, which is derived from natto, and have been shown to effectively raise serum K2 levels. The longer half-life of MK-7 means it remains in the bloodstream longer, allowing it to reach and benefit extra-hepatic tissues like bones and arteries more effectively.
Comparing Vitamin K2 Sources
| Source | Primary Subtype | Bioavailability | Relative Amount of K2 | Best for... |
|---|---|---|---|---|
| Natto | MK-7 | Excellent | Highest | Vegetarians/Vegans needing a concentrated food source. |
| Cheese (Aged Gouda, Brie) | MK-8, MK-9 | Good | Moderate to High | Integrating into a Western diet, dairy consumers. |
| Goose/Chicken Liver | MK-4 | Good | High | Non-vegetarians, organ meat consumers. |
| Pasture-Raised Egg Yolks | MK-4 | Good | Moderate | Everyday dietary intake, fat-soluble vitamin absorption. |
| Supplements (MK-7) | MK-7 | Excellent | Consistent | Reliably achieving therapeutic K2 levels, convenience. |
| Sauerkraut | MK-7 | Moderate | Low to Moderate | Fermented food fans, general gut health. |
The Role of Vitamin K2 in Health
The interest in vitamin K2 extends beyond mere quantity to its vital health roles, particularly its synergistic relationship with vitamin D. While vitamin D promotes calcium absorption, vitamin K2 activates proteins like osteocalcin and matrix Gla protein (MGP) to ensure that calcium is directed to the bones and teeth, rather than accumulating in soft tissues like arteries.
Cardiovascular Health
Calcium buildup in the arteries is a major risk factor for heart disease. Research has shown that a higher intake of vitamin K2, specifically MK-7, is associated with a reduced risk of coronary heart disease and severe aortic calcification. The activation of MGP by vitamin K2 is a key mechanism behind this protective effect, as MGP is a potent inhibitor of vascular calcification.
Bone Density and Strength
Just as important is K2's contribution to skeletal health. By activating osteocalcin, vitamin K2 helps bind calcium to the bone matrix, promoting mineralization and strengthening the bone structure. This process is crucial for preventing conditions like osteoporosis, especially in postmenopausal women. Studies in Japan have even shown that high doses of MK-4 can be an effective treatment for osteoporosis.
Which Form of K2 is Superior?
While MK-4 is found in animal products and plays an important role, most research points to MK-7 as the more effective form for systemic health benefits. Its longer half-life allows it to accumulate and remain active in the bloodstream for a longer period, making it more readily available for extra-hepatic tissues like the arteries and bones. This difference in bioavailability explains why supplementing with MK-7 is often considered the superior choice for targeting bone and heart health, even though MK-4 is also essential. For a natural dietary approach, a combination of both is ideal, but for targeted supplementation, MK-7 is typically the focus.
Conclusion: Finding Your Best Source
Ultimately, there is no single "best" source of vitamin K2 for everyone; it depends on your dietary preferences and health goals. For a maximal, natural dose of the highly bioavailable MK-7, natto is the clear winner, though its taste can be prohibitive. Animal products like grass-fed cheeses, egg yolks, and liver are excellent options for those who eat meat and dairy, providing the MK-4 subtype. For a reliable, consistent, and potent dose without changing your diet, a high-quality MK-7 supplement is the most practical choice. No matter the source, increasing your intake of vitamin K2 can have profound benefits for your bone and cardiovascular health. For personalized advice, consult a healthcare professional. You can also explore more dietary information at the National Institutes of Health website.
