Understanding the K Vitamins
Vitamin K is a family of fat-soluble vitamins essential for various bodily functions, most notably blood clotting and calcium metabolism. It exists in two primary forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones, or MKs). While K1 is abundant in leafy green vegetables, K2 is predominantly produced by bacteria, explaining its presence in fermented foods and some animal products. Within the Vitamin K2 family, there are several subtypes, designated by numbers like MK-4 and MK-7, which indicate the length of their side chain. The highly bioavailable MK-7 form is of particular interest due to its longer half-life, which allows it to remain active in the body for an extended period, providing more consistent support for bone and cardiovascular health.
Fermented Foods: The Top Source of K2MK7
For those wondering what are the sources of k2mk7, the answer begins with bacterial fermentation. Certain strains of bacteria produce this long-chain menaquinone, concentrating it in the foods they ferment. The undisputed champion of MK-7 content is a traditional Japanese food with a sticky texture and pungent flavor.
Natto (Fermented Soybeans)
Natto is a traditional Japanese dish made from soybeans fermented with Bacillus subtilis bacteria. It is, by far, the richest dietary source of K2MK7, providing well over 1,000 micrograms per 100-gram serving. For context, this is a massive amount compared to other sources. Its high concentration and favorable bioavailability make it a key food for anyone seeking to maximize their MK-7 intake. While its distinctive taste may be an acquired one for many in Western cultures, its nutritional benefits are substantial.
Other Fermented Foods
While natto is an outlier, other fermented foods also contain varying levels of K2. The bacteria used in fermentation are the primary factor in determining the MK content.
- Cheeses: Hard and soft cheeses, particularly aged varieties, are excellent sources of different MKs. Gouda and Brie are notable for their MK-7 content, while others contain MK-8 and MK-9. The bacterial cultures used, such as Lactococcus species, produce menaquinones during the cheese-making process.
- Sauerkraut: Fermented cabbage can contain small to moderate amounts of MK-7, though generally much less than natto. The bacterial fermentation process, typically involving Lactobacillus species, is responsible for its MK content.
- Kefir and Yogurt: These fermented milk products can be moderate sources of K2, with the menaquinone content varying based on the bacterial strains used.
Animal Products as a Source of Vitamin K2
While MK-7 is prominent in fermented foods, animal products are a primary source of menaquinone-4 (MK-4), another form of Vitamin K2. Some animal products can also contain smaller amounts of MK-7, depending on their diet.
Rich Animal Sources of K2
- Organ Meats: Goose and chicken liver are particularly concentrated sources of MK-4. Goose liver pate can contain very high levels.
- Grass-Fed Dairy and Eggs: Products from grass-fed animals tend to have higher levels of Vitamin K2 because the animals consume grass rich in Vitamin K1, which their gut bacteria and tissues convert to K2. This includes butter, full-fat dairy, and egg yolks from pasture-raised chickens.
- Certain Meats: Fatty cuts of meat, including chicken thighs and legs, can also contain notable amounts of MK-4.
K2MK7 Supplements
For those who cannot or prefer not to obtain sufficient K2MK7 from dietary sources, supplements are a highly effective alternative. High-quality supplements derived from natural fermentation using Bacillus subtilis are widely available. It is important to look for MK-7 supplements that specify natural fermentation, as this process ensures a high percentage of the bioactive all-trans isomer.
The MK-7 vs. MK-4 Comparison
When considering dietary sources of K2, it's helpful to understand the different properties of MK-7 and MK-4.
| Feature | Menaquinone-7 (MK-7) | Menaquinone-4 (MK-4) |
|---|---|---|
| Primary Source | Fermented foods (especially natto) | Animal products (grass-fed, organ meats) |
| Absorption | Highly bioavailable and efficiently absorbed | Readily absorbed, but tissue levels don't increase as much with supplementation |
| Half-Life | Long half-life (approx. 72 hours) | Short half-life (approx. 1-2 hours) |
| Distribution | Wider distribution to extrahepatic tissues like bones and blood vessels | Concentrated in the liver and other specific organs |
| Bioactivity | Very effective at activating osteocalcin and MGP | Also effective, particularly at higher doses, but MK-7 is more potent for bone health |
Conclusion: Sourcing Your K2MK7
Understanding what are the sources of k2mk7 reveals that this important nutrient is derived mainly from bacterial processes. While the Japanese fermented soybean dish natto is the most concentrated dietary source, other options include aged cheeses, sauerkraut, and grass-fed animal products. For those with dietary restrictions or who find these foods unappealing, high-quality supplements offer a reliable way to meet daily needs. The key takeaway is that diverse and intentional food choices are often necessary to ensure adequate intake of K2, especially the potent MK-7 form, for robust bone and cardiovascular health. For a deeper scientific dive into the molecular pathways involved in K2 production and its benefits, explore the research compiled by the National Institutes of Health.
The Role of Gut Health
It's worth noting that some Vitamin K2 is produced by the beneficial bacteria within the human gut microbiome. A healthy and balanced gut flora can contribute to the body's overall menaquinone supply, though the efficiency of absorption from this source is still debated. Therefore, including probiotic-rich foods like kefir, yogurt, and sauerkraut in your diet not only provides a direct source of K2 but can also support a healthy gut environment that promotes endogenous production. However, relying solely on gut bacteria for MK-7 may not be sufficient for optimal levels, making dietary intake and supplementation more reliable strategies.
Combining Sources for Maximum Benefit
For a comprehensive approach to Vitamin K2 intake, a combination of sources is often recommended. This ensures you are receiving a mix of menaquinone types, including both MK-4 and MK-7, which play distinct but synergistic roles in the body. For instance, pairing a diet rich in grass-fed dairy with occasional servings of fermented foods like cheese and natto can provide a broad spectrum of Vitamin K2. When supplementing, some products combine both forms to offer a balanced dose. Always consider your individual health needs and consult a healthcare provider, especially if you take blood-thinning medication.
