What is Menaquinone?
Menaquinone, commonly known as Vitamin K2, is a fat-soluble vitamin and a family of compounds that are essential for several biological processes. While its counterpart, Vitamin K1 (phylloquinone), primarily supports blood clotting, menaquinone has been shown to play a more prominent role in bone health and cardiovascular health. Menaquinones, abbreviated as MK-n, differ based on the length of their side chain, with common forms being MK-4, MK-7, MK-8, and MK-9. The human body can convert some K1 into MK-4, but dietary sources of K2, particularly the long-chain versions like MK-7, are highly bioavailable and are considered crucial for extra-hepatic tissue health.
Fermented Foods: The Richest Sources of Menaquinone
Fermentation is a primary process through which bacteria synthesize menaquinones, making fermented foods the richest dietary sources of K2. Here are some of the most notable examples:
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Natto: This traditional Japanese dish of fermented soybeans is the most potent known food source of Vitamin K2, specifically menaquinone-7 (MK-7). The bacteria Bacillus subtilis natto is responsible for its exceptionally high MK-7 content. While its sticky texture and strong flavor may be an acquired taste for some, natto offers significant health benefits, especially for bone mineral density.
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Cheeses: Certain types of cheese, particularly hard and aged varieties, are excellent sources of long-chain menaquinones like MK-8, MK-9, and MK-10. The menaquinone content in cheese is dependent on the type of cheese, the starter cultures used, and the ripening time. Examples of cheese high in K2 include Gouda, Edam, and some blue cheeses.
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Sauerkraut: This fermented cabbage product is a source of menaquinone-7, though generally in much lower concentrations than natto. The fermentation process provides beneficial probiotics for gut health, which can also help the body produce K2.
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Fermented milk products: Products like kefir and some whole-milk yogurts contain menaquinones synthesized by the bacterial cultures used in their production.
Animal Products: Sources of Menaquinone-4
Animal products provide a different form of menaquinone, primarily MK-4. Unlike the long-chain menaquinones found in fermented foods, MK-4 is produced in animal tissues by converting other forms of vitamin K, such as K1 from green plants. Key sources include:
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Chicken: Meat, particularly the dark meat of chicken, is a notable source of MK-4.
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Egg Yolks: The yolks of eggs contain moderate amounts of MK-4. The K2 content can vary based on the chicken's diet.
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Organ Meats: Liver from various animals contains significant amounts of MK-4.
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Butter: As a dairy product, butter contains some menaquinone, primarily MK-4.
Menaquinone vs. Phylloquinone: Key Differences and Bioavailability
| Feature | Menaquinone (Vitamin K2) | Phylloquinone (Vitamin K1) |
|---|---|---|
| Primary Sources | Fermented foods (natto, cheese), animal products (egg yolks, liver, butter) | Leafy green vegetables (spinach, kale, broccoli), vegetable oils |
| Synthesis | Produced by bacteria during fermentation and in animal tissues via conversion | Synthesized by plants |
| Bioavailability | Highly bioavailable, particularly long-chain MK-7 | Less bioavailable; tightly bound to plant chloroplasts |
| Absorption Site | Absorbed in the small and large intestines | Primarily absorbed in the small intestine |
| Tissue Distribution | Widely distributed in the body, including extra-hepatic tissues like bone and arteries | Stored mainly in the liver |
| Health Focus | Strong links to bone mineralization and cardiovascular health | Primarily associated with blood coagulation |
Gut Microbiota and Menaquinone Production
While dietary intake is the most reliable way to obtain menaquinone, the bacteria in the human gut can also synthesize it. Certain bacteria in the gut microbiome can produce menaquinones, mainly longer-chain varieties like MK-10 and MK-11. However, the bioavailability of K2 produced in the gut is limited, as most absorption happens further up in the digestive tract. This is why dietary intake, especially of high-bioavailability forms like MK-7, is considered the most reliable source for maintaining optimal vitamin K2 levels. Consuming fermented foods not only provides a direct source of K2 but also introduces beneficial bacteria that can support a healthy gut microbiome.
How to Maximize Menaquinone Intake
To ensure adequate menaquinone intake, a balanced diet incorporating a variety of sources is recommended. If you can tolerate it, a small serving of natto provides a potent dose of MK-7. Incorporating aged cheeses, kefir, or sauerkraut into your meals is an accessible option. For those who consume animal products, including grass-fed meats, eggs, and some poultry, can contribute to your MK-4 intake. Given that vitamin K is fat-soluble, consuming K2-rich foods with some healthy fat can enhance absorption.
Conclusion
Menaquinone (Vitamin K2) is a vital nutrient for bone and cardiovascular health, with key dietary sources being fermented foods and animal products. Unlike Vitamin K1 from leafy greens, menaquinone is highly bioavailable and more effectively utilized by extra-hepatic tissues. The Japanese fermented soybean product natto is the richest source of the potent MK-7, while animal products primarily offer MK-4. For Western diets, aged cheeses and other fermented foods provide a substantial source. A diverse diet that includes a mix of these sources can help ensure adequate menaquinone levels for long-term health.
Authoritative Reference
For detailed information on menaquinones, consult the National Institutes of Health (NIH) Office of Dietary Supplements fact sheet on Vitamin K.
