Understanding the Forms of Vitamin K2
Vitamin K is a fat-soluble vitamin essential for blood coagulation and calcium regulation. While vitamin K1 is primarily found in leafy greens and used by the liver for blood clotting, vitamin K2 (menaquinones) is found in animal and fermented foods and plays a more significant role in extrahepatic tissues, such as bones and blood vessels. The most researched subtypes of K2 are MK-4 and MK-7, each with distinct properties.
Vitamin K2 as MK-4
MK-4 is a short-chain form of vitamin K2 found in animal products like meat, eggs, and high-fat dairy. It is also the main form of K2 created in the body from the conversion of vitamin K1. However, MK-4 has a very short half-life, meaning it is cleared from the blood rapidly, within hours of consumption. Research indicates that at nutritional supplemental doses, MK-4 is poorly absorbed and does not significantly increase serum levels. To achieve therapeutic effects for conditions like osteoporosis, higher, frequent intake is generally required.
Vitamin K2 as MK-7
MK-7 is a long-chain form of vitamin K2, naturally produced through bacterial fermentation, with natto (fermented soybeans) being an exceptionally rich source. Unlike MK-4, MK-7 has a much longer half-life and remains active in the bloodstream for several days, allowing for consistent and sustained support for extrahepatic tissues. This superior bioavailability means that smaller, once-daily supplementation of MK-7 may be sufficient to raise and maintain effective levels in the body.
The Crucial Role in Calcium Regulation
One of vitamin K2's most important functions is activating specific vitamin K-dependent proteins (VKDPs) that regulate calcium metabolism. The two key VKDPs are Osteocalcin and Matrix Gla Protein (MGP).
- Osteocalcin: This protein, produced by osteoblasts, binds calcium to the bone matrix to promote proper mineralization and density. K2 ensures Osteocalcin is fully carboxylated and active.
- Matrix Gla Protein (MGP): Found in arterial walls and soft tissues, MGP inhibits soft tissue calcification by preventing calcium from depositing in areas where it shouldn't be, such as the arteries. K2 is required to activate MGP, which helps maintain arterial elasticity and cardiovascular health.
MK-4 vs. MK-7: A Comparison for Your Health
Understanding the physiological differences between these two forms is key to choosing the right supplement, especially if you have specific health goals. When it comes to effective delivery to target tissues, MK-7 has a significant advantage.
| Feature | Vitamin K2 (MK-4) | Vitamin K2 (MK-7) |
|---|---|---|
| Source | Animal products (meat, dairy, eggs); converted from K1. | Fermented foods (natto, cheese); bacterial synthesis. |
| Bioavailability | Poor at nutritional levels; does not significantly raise serum levels. | Excellent; well-absorbed and accumulates in the bloodstream. |
| Half-Life | Short (approx. 6-8 hours); cleared quickly from the blood. | Long (approx. 72 hours); stays in the body longer for sustained action. |
| Intake Frequency | Requires consistent intake for clinical effects. | Effective with a single daily intake. |
| Extrahepatic Benefits | Less effective for systemic delivery to bones and arteries at typical intake levels. | More effective for targeting bones and soft tissues due to longer half-life. |
| Primary Role | The main form of K2 found and used in some tissues, but intake doesn't increase blood levels well. | A more bioavailable precursor that the body can convert to MK-4 in tissues where it's needed. |
How to Choose the Best Form of Vitamin K2
For most individuals seeking systemic benefits for bone and cardiovascular health, MK-7 is the superior choice for supplementation due to its high bioavailability and long half-life. It provides a sustained supply of vitamin K2 to activate key proteins, potentially preventing calcium from building up in arteries and promoting its proper integration into bones. A daily intake of vitamin K2 may offer health benefits.
When selecting an MK-7 supplement, prioritize high-quality products. Look for supplements that guarantee a high percentage of the trans-isomer of MK-7, as this is the biologically active form. While food sources like natto provide abundant MK-7, supplementation is a practical alternative for those who don't regularly consume it.
Conclusion: Making the Right Choice for Your Health
Ultimately, the best form of vitamin K2 for supplementation is MK-7. While MK-4 is physiologically relevant and the form primarily used by the body in extrahepatic tissues, consuming MK-7 is a far more effective way to deliver sustained vitamin K2 to these areas. Its long half-life and superior bioavailability ensure that you get consistent, measurable benefits for your bone and heart health, potentially without the need for frequent intake required with MK-4. Consulting a healthcare professional before starting any new supplement is recommended, especially if you are taking blood-thinning medication.
Important Considerations
- Always choose a reputable brand with third-party testing to ensure product quality and purity.
- If taking vitamin D3, pairing it with vitamin K2 is often recommended, as they work synergistically to direct calcium.
- Individuals on blood thinners like warfarin must consult a doctor before supplementing with vitamin K2, as it can interfere with the medication.
- Consider an oil-based formula or taking your supplement with a meal containing fat to maximize absorption, as vitamin K is fat-soluble.
