Understanding Vitamin K2: The Lesser-Known K
Vitamin K is a fat-soluble nutrient with two main forms: K1 (phylloquinone), found primarily in leafy greens, and K2 (menaquinone), found in animal products and fermented foods. While K1 is important for blood clotting, K2 plays a critical role in directing calcium to the right places in the body—namely, your bones and teeth—while keeping it out of your arteries and soft tissues. A sufficient intake of K2 is therefore crucial for maintaining strong bones and promoting cardiovascular health. However, because most Western diets are low in K2-rich foods, supplementation is often considered alongside dietary changes.
Sourcing Vitamin K2 from Your Diet
For those who prefer a food-first approach, there are several excellent sources of vitamin K2, which come in different menaquinone (MK) subtypes. The two most studied are MK-4 and MK-7.
Fermented Foods (MK-7)
Fermented foods are a key source of the long-chain MK-7 form of vitamin K2, which has high bioavailability and a longer half-life in the bloodstream compared to MK-4.
- Natto: This traditional Japanese dish of fermented soybeans is, by far, the richest dietary source of K2. For those who can acquire a taste for it, natto is a powerful addition to the diet.
- Cheeses: Certain hard and soft cheeses, like Gouda, Brie, and some cheddars, are good sources of vitamin K2. The fermentation process is responsible for producing the menaquinones.
- Sauerkraut: While containing smaller amounts compared to natto, fermented cabbage can contribute to your K2 intake and offers a variety of other probiotic benefits.
- Kefir and other fermented dairy: Fermented milk products can also contain some vitamin K2.
Animal-Based Foods (MK-4)
Animal products, especially from grass-fed animals, are the primary source of the MK-4 form of vitamin K2.
- Goose and Chicken Liver: Organ meats are excellent sources of MK-4. Goose liver pate and chicken liver are particularly rich.
- Egg Yolks: The yolks from pastured or free-range chickens are good sources of MK-4. The K2 content varies depending on the hen's diet.
- Grass-Fed Butter: Butter from cows that graze on grass contains significantly more MK-4 than butter from grain-fed cows.
- Fatty Fish: While not the highest source, certain fatty fish like salmon and sardines contain some vitamin K2.
Optimizing Vitamin K2 Absorption
Vitamin K2 is fat-soluble, meaning it is best absorbed when consumed with dietary fat. To maximize the absorption of K2 from food or supplements, consider these strategies:
- Combine K2-rich foods with healthy fats, such as olive oil, avocado, or nuts.
- Take K2 supplements during a meal that contains fat.
- Pairing vitamin K2 with vitamin D3 is highly recommended, as they work synergistically to regulate calcium. Many high-quality supplements combine both for this reason.
Should You Choose Supplements?
For many people, consistently consuming enough dietary vitamin K2 can be challenging due to taste preferences (like with natto) or the variability of nutrient content in animal products. Supplements offer a reliable and concentrated source. When choosing a supplement, consider the following.
MK-7 vs. MK-4 Supplements
While both forms are available in supplements, MK-7 is generally considered superior due to its higher bioavailability and longer half-life. MK-4 has a shorter half-life, requiring more frequent administration for consistent levels. Most MK-4 found in supplements is synthetic.
Considerations for Supplementation
Individuals with certain health conditions or those taking blood thinners like warfarin should consult a healthcare professional before supplementing, as K2 can affect blood clotting.
Comparison: Dietary Sources vs. Supplementation
| Feature | Dietary Sources | Supplementation (MK-7) |
|---|---|---|
| Source | Fermented foods (natto, cheese), animal products (liver, egg yolks, grass-fed butter) | Extracted from natto or synthesized |
| Primary Form | MK-7 from natto, MK-4 from animal products | Typically MK-7 for superior bioavailability |
| Convenience | Requires consistent sourcing and consumption of specific foods, which may be unpalatable for some | Easy to take, offering convenience |
| Nutrient Synergy | Comes with other beneficial nutrients present in the food matrix | Can be formulated with synergistic nutrients like Vitamin D3 for maximum effectiveness |
| Consistency | Varies greatly based on the source's processing, fermentation, or animal's diet | Can provide a consistent amount |
| Cost | Can be more expensive to source high-quality animal and fermented products | Can be a cost-effective way to support intake, but price varies by brand |
Conclusion
Ultimately, the best way to get vitamin K2 involves a combination of dietary awareness and, for many, strategic supplementation. Including natural sources like natto, grass-fed dairy, and eggs is an excellent foundation for your intake. For those who find these dietary options challenging or unreliable, a high-quality MK-7 supplement is a highly effective and convenient alternative. To maximize the benefit, always take vitamin K2—whether from food or a supplement—along with a source of dietary fat. By combining these approaches, you can effectively support optimal vitamin K2 levels, potentially contributing to long-term bone density and cardiovascular health. For more insights on this vital nutrient, Healthline provides a comprehensive overview of its functions and benefits.
