Vitamin K is an essential fat-soluble nutrient, most famously for its role in blood coagulation. However, the lesser-known but equally vital vitamin K2, or menaquinone, is crucial for directing calcium to the right places in the body—namely, the bones—and preventing it from accumulating in soft tissues like the arteries. This critical function is central to both bone and cardiovascular health. Within the vitamin K2 family, two forms—MK-4 and MK-7—are the most prevalent and studied. While they share fundamental roles, their differences in source, half-life, and bioavailability significantly impact their effectiveness.
The Fundamental Differences: MK-4 vs. MK-7
MK-4, or menaquinone-4, is the most common form of vitamin K2 found in animal products, including grass-fed dairy, egg yolks, and organ meats. It is also the predominant form of vitamin K in many extra-hepatic tissues, such as the brain, pancreas, and arterial walls. The body can convert other forms of vitamin K, including K1 and MK-7, into MK-4. However, at typical nutritional levels, MK-4 has a very short half-life of just a few hours and is quickly cleared from the bloodstream. As a result, maintaining sufficient blood levels for systemic benefits would require frequent, very high intake levels. The MK-4 found in many supplements is often synthetic.
MK-7, or menaquinone-7, is produced through bacterial fermentation and is most famously found in the Japanese fermented soybean dish, natto. Unlike MK-4, MK-7 boasts superior bioavailability and a remarkably long half-life, remaining in the bloodstream for up to 72 hours. This sustained presence allows MK-7 to be effectively transported to extra-hepatic tissues over a longer period, making it more efficient. For this reason, MK-7 is often considered a practical and potent form of K2 for general supplementation.
Comparison of MK-4 and MK-7
| Feature | Menaquinone-4 (MK-4) | Menaquinone-7 (MK-7) |
|---|---|---|
| Primary Sources | Animal products (grass-fed butter, eggs, liver). | Fermented foods (natto, certain cheeses like Gouda). |
| Source in Supplements | Often synthetic. | Extracted from natto or created via bacterial fermentation. |
| Half-Life | Very short; cleared in 6–8 hours. | Long; remains in blood for up to 72 hours. |
| Absorption | Poor absorption at nutritional levels; doesn't significantly raise serum levels. | Excellent absorption; accumulates in the bloodstream with consistent intake. |
| Effective Need | High levels may be used for certain therapeutic purposes. | Effective for systemic benefits with regular intake. |
| Best for | Tissue-specific concentration; used in high levels for certain therapeutic purposes. | Broad systemic effects on bone density and cardiovascular health; daily support. |
The Superiority of MK-7 for Consistent Benefits
Clinical research clearly highlights MK-7's advantages for general supplementation aimed at bone and cardiovascular health. Its exceptional half-life means that a single, small daily intake is sufficient to maintain steady, beneficial levels of K2 in the blood. This prolonged circulation allows MK-7 to efficiently activate the crucial proteins osteocalcin and Matrix Gla Protein (MGP) in extra-hepatic tissues, directing calcium to the bones and preventing its harmful buildup in the arteries. For individuals seeking broad, consistent support for these areas, MK-7's bioavailability and ease of use make it a favorable choice.
The High-Level, Tissue-Specific Role of MK-4
While MK-7 shines for its systemic efficiency, MK-4 is not without its specific functions. The body naturally converts K1 and MK-7 into MK-4, and MK-4 is the form that accumulates in specific tissues, playing a unique, tissue-specific role, particularly in the brain and nervous system. However, the extremely high levels (in the milligrams) that may be used for MK-4 to provide systemic effects make it impractical for routine supplementation for most people. At lower, nutritional levels, MK-4 has poor bioavailability and does not raise serum levels effectively. For this reason, supplemental MK-4 may be more relevant in high-level therapeutic contexts, particularly in some specialized medical treatments in Japan for osteoporosis.
How to Choose the Right Form of K2
The choice between MK-4 and MK-7 often depends on your specific health goals and considerations. For the vast majority of people looking to support their bone mineral density and cardiovascular health through routine supplementation, MK-7 is the most logical option due to its high bioavailability and long half-life. Its steady, consistent delivery makes it a reliable choice for activating vitamin K-dependent proteins throughout the body. Individuals who want to maximize their intake of tissue-specific MK-4 might consider incorporating more animal products from grass-fed sources, as supplementation at certain levels may not be suitable for everyone. Many high-quality supplements today offer both forms in a single formula, attempting to provide the potential benefits of both.
Conclusion
While MK-4 and MK-7 are both vital forms of vitamin K2, their differences in absorption, half-life, and general intake levels are significant. For daily, practical supplementation aimed at supporting bone and cardiovascular health, MK-7's superior bioavailability and long half-life make it a more effective and efficient choice for most individuals. MK-4, while important for specific tissues in the body, is not well-absorbed at typical supplement levels and may require high levels to achieve systemic effects in some cases. Ultimately, your personal health goals will guide your decision, but for broad health support, MK-7 is often favored. A balanced diet rich in fermented foods and healthy animal products can also provide both forms naturally.
For more detailed scientific information on the bioavailability of MK-4 versus MK-7, you can review this study from the National Institutes of Health.
