Natto: The Unrivaled Champion of Vitamin K2
While many foods contain vitamin K, very few are packed with the highly bioavailable menaquinone-7 (MK-7) form of vitamin K2, and none come close to natto. This Japanese dish of fermented soybeans is created by fermenting soybeans with the bacterium Bacillus subtilis. This fermentation process is what generates the exceptionally high levels of K2, specifically MK-7. Just one ounce of natto can provide a massive dose of vitamin K2, far exceeding the daily recommended intake for adults.
For many in the Western world, natto's unique pungent flavor and sticky, stringy texture can be an acquired taste. However, for those seeking the most concentrated source of vitamin K2 from food, it remains the gold standard. In Japan, regular natto consumption is associated with positive health outcomes, particularly related to bone density.
Other Excellent Sources of Vitamin K2
Beyond natto, other food sources, though containing lower amounts, are more common in Western diets and can still contribute significantly to your vitamin K2 intake. These are typically animal products or fermented cheeses, containing primarily the MK-4 and longer-chain menaquinones (MK-8, MK-9). It is important to note that the K2 content in animal products depends heavily on the animal's diet. Grass-fed animals, for example, tend to produce dairy and meat products with higher K2 levels.
Organ Meats:
- Goose Liver Pâté: One of the richest animal-based sources, providing a high concentration of MK-4.
- Beef and Chicken Liver: Pan-fried liver contains notable amounts of vitamin K2 and is an excellent source of other essential nutrients like iron and vitamin A.
Dairy Products:
- Hard and Soft Cheeses: Aged cheeses like Gouda and Brie are known for their high menaquinone content, especially MK-9. Cheeses made from grass-fed milk are particularly good sources.
- Butter and Ghee: Butter, especially from grass-fed cows, contains the MK-4 form of K2.
Eggs:
- Egg Yolks: A concentrated source of fat-soluble vitamins, with a good amount of MK-4. The amount can vary based on the hen's diet.
Fermented Foods:
- Sauerkraut: While significantly lower in K2 than natto, sauerkraut still offers a small contribution along with beneficial probiotics.
Comparing Vitamin K1 and K2 Sources
To put the concentration of K2 in natto into perspective, it's helpful to compare it with other sources, both K1 and K2. While K1 is more common in vegetables, K2 is less abundant and produced by bacteria during fermentation or found in animal fats.
| Food Source | Type of Vitamin K | Vitamin K Content (per 100g) | Primary Menaquinone Type | Bioavailability |
|---|---|---|---|---|
| Natto | K2 (Menaquinone) | 939 - 1103.4 mcg | MK-7 | Very High |
| Goose Liver Pâté | K2 (Menaquinone) | 369.0 mcg | MK-4 | High |
| Hard Cheeses (e.g., Gouda) | K2 (Menaquinone) | 76.3 mcg | MK-9 | Moderate |
| Beef Liver | K2 (Menaquinone) | 106.0 mcg | MK-4 | Moderate |
| Cooked Kale | K1 (Phylloquinone) | 418.5 mcg | K1 | Lower |
| Cooked Spinach | K1 (Phylloquinone) | 540.7 mcg | K1 | Lower |
This table illustrates the massive difference in concentration, especially when comparing natto to other sources, including the K1-rich leafy greens. While your body can convert some K1 to K2, the conversion is often inefficient, making direct dietary sources of K2 more impactful.
The Health Benefits of Vitamin K2
Beyond its well-known role in blood clotting, vitamin K2 provides significant benefits for both bone and cardiovascular health. These benefits are attributed to its function in activating specific proteins.
- Bone Mineral Density: Vitamin K2 activates osteocalcin, a protein that binds calcium to the bone matrix. This process helps ensure calcium is deposited correctly in bones, increasing bone strength and reducing fracture risk, especially in postmenopausal women.
- Cardiovascular Health: K2 helps regulate calcium, preventing its buildup in soft tissues like arteries and blood vessels. This mechanism helps prevent vascular calcification, a major contributor to cardiovascular disease.
- Dental Health: Research suggests that K2 may contribute to dental health by helping to build new dentin and regulating calcium that promotes strong teeth.
Challenges and Considerations
While natto is the clear winner for vitamin K2 content, its cultural and sensory profile poses a challenge for many outside of East Asia. This is why other sources, though less potent, are vital for those seeking to boost their K2 intake. Furthermore, it is important to remember that K2 is a fat-soluble vitamin, meaning it is absorbed best when consumed with dietary fat. This is naturally accommodated when consuming dairy, meat, and eggs, but those eating plant-based K2 sources like natto should pair them with healthy fats like olive oil or avocado.
Finally, for individuals who cannot or choose not to eat natto, supplementation is a viable option. Many supplements on the market provide MK-7, offering a convenient way to ensure adequate intake. As with any supplement, it is best to consult a healthcare provider to determine the right dosage for your needs, especially for those on blood-thinning medication.
Conclusion
In summary, natto stands out as the single highest source of vitamin K2, delivering an unparalleled concentration of the highly beneficial MK-7 form. However, for those who find its taste challenging, other excellent dietary sources, including goose liver, aged cheeses, grass-fed butter, and egg yolks, can provide significant amounts of K2, predominantly in the MK-4 form. Prioritizing a varied diet that includes these options can help support optimal bone density and cardiovascular health. While K1 from leafy greens is also important, direct dietary intake of K2 is particularly valuable for reaping its unique benefits for calcium utilization in the body. If dietary options are limited, high-quality supplements offer a reliable alternative.
