What Is Vitamin K2 and How Does K2-7 Fit In?
To understand the relationship, it helps to view Vitamin K as a family of fat-soluble compounds. This family includes Vitamin K1 (phylloquinone), which comes from leafy greens, and Vitamin K2 (menaquinones). Vitamin K2 is not a single entity but a group of structurally related compounds denoted as MK-n, where 'n' represents the number of side-chain chemical units. Therefore, Vitamin K2 is the general category, while K2-7 (Menaquinone-7) is a specific type within that family, characterized by a side chain of seven isoprene residues.
Menaquinones with shorter side chains, such as MK-4, are found primarily in animal products like meat and eggs. Longer-chain menaquinones like MK-7 are synthesized by specific bacteria and are most abundant in fermented foods such as the Japanese dish natto and some cheeses. The side-chain length significantly impacts how the body absorbs and utilizes the vitamin, which is why K2-7 is distinct from other forms, such as MK-4.
The Critical Differences Between K2 (MK-4) and K2-7 (MK-7)
While both forms activate crucial vitamin K-dependent proteins (VKDPs) involved in blood clotting and calcium metabolism, they differ significantly in their physiological effects due to differences in their structure and pharmacokinetics. The most important distinctions relate to half-life and bioavailability.
- Half-Life: After absorption, MK-4 has a very short half-life, meaning it is cleared from the bloodstream rapidly, typically within a few hours. In contrast, MK-7 has a much longer half-life and remains detectable in the body for days after intake.
- Bioavailability and Distribution: The long half-life of MK-7 allows it to accumulate in the bloodstream and be more effectively distributed to extra-hepatic tissues throughout the body, such as bones and blood vessels. This is crucial for its roles in improving bone density and reducing arterial calcification. MK-4, because of its rapid clearance, has less impact on these extra-hepatic tissues at typical nutritional doses.
The Role of K2-7 in a Healthy Diet
The superior bioavailability of K2-7 makes it particularly effective for extra-hepatic health. It is a key player in directing calcium to the right places in the body.
A list of key health benefits associated with K2-7 include:
- Bone Health: MK-7 activates osteocalcin, a protein that binds calcium and integrates it into the bone matrix, improving bone mineral density and strength. Some studies have shown that MK-7 supplementation can help decrease age-related bone loss.
- Cardiovascular Health: K2-7 activates Matrix Gla Protein (MGP), which prevents calcium from depositing in soft tissues like artery walls, helping to reduce arterial stiffness and calcification. Research has linked higher K2-7 intake to a lower risk of coronary heart disease.
- Dental Health: Similar to its role in bones, K2-7 helps support the mineralization of teeth by directing calcium into dentin.
The Best Food Sources of Vitamin K2
Incorporating different forms of Vitamin K2 into your diet is beneficial. Here is a breakdown of common food sources for each major form:
- Sources of MK-4: Animal-based foods like chicken, beef, egg yolks, and butter are primary dietary sources of MK-4.
- Sources of MK-7: The single best source of MK-7 is natto, a fermented Japanese soybean product. Other fermented foods and aged cheeses also contain significant amounts of menaquinones.
Comparison Table: Vitamin K2 (MK-4) vs. K2-7 (MK-7)
| Feature | Vitamin K2 (MK-4) | Vitamin K2-7 (MK-7) |
|---|---|---|
| Structure | Short-chain menaquinone (4 isoprene units) | Long-chain menaquinone (7 isoprene units) |
| Primary Source | Animal products (e.g., egg yolks, meat) | Fermented foods (e.g., natto, specific cheeses) |
| Half-Life | Very short (cleared in hours) | Very long (lasts for days) |
| Bioavailability | Poor at nutritional doses in the serum | Excellent, accumulates in the bloodstream |
| Extra-Hepatic Activity | Less effective due to short half-life | Highly effective in bones and arteries |
| Dosage | Effective at higher, less frequent doses | Effective at lower, once-daily doses |
Choosing the Right Supplement for Your Nutrition Diet
For general extra-hepatic health benefits, such as supporting bone density and arterial health, MK-7 is widely considered the superior choice due to its longer half-life and greater bioavailability. When selecting a supplement, ensure it clearly specifies the form of Vitamin K2. For those with special dietary needs or restrictions, such as vegans, MK-7 is often sourced from fermented soy and is a more suitable option than animal-sourced MK-4.
If you take anticoagulant medication like warfarin, it is critical to consult with a healthcare provider before taking any Vitamin K supplement, as it can interfere with these medications. For the general population, Vitamin K2 is considered safe and well-tolerated, even at higher doses.
Conclusion
In conclusion, Vitamin K2 and K2-7 are not the same; K2-7 (MK-7) is a specific, long-chain form of the broader Vitamin K2 family. The superior half-life and bioavailability of MK-7 make it a particularly effective dietary or supplemental form for targeting extra-hepatic tissues like bones and arteries. By understanding the distinct roles of different menaquinones, you can optimize your nutrition diet to support your long-term bone and cardiovascular health. For those seeking targeted support for arterial and bone health, prioritizing MK-7 through fermented foods or high-quality supplements is a wise choice. More evidence on the nuances of this vitamin continues to emerge, underscoring its importance beyond its classic function in coagulation. A thorough review of Vitamin K's functions can be found on the National Institutes of Health website.
