Understanding Vitamin K2 and Its Importance
Vitamin K is a fat-soluble vitamin essential for several bodily functions, most notably blood clotting and proper calcium utilization. While Vitamin K1 (phylloquinone) is primarily found in leafy greens and used for coagulation in the liver, Vitamin K2 (menaquinone) plays a more significant role in directing calcium towards the bones and teeth and away from soft tissues like arteries and kidneys. The most common and well-studied forms of Vitamin K2 are menaquinone-4 (MK-4) and menaquinone-7 (MK-7). The choice between these two forms is a critical consideration for those seeking to optimize their cardiovascular and bone health through supplementation.
MK-4: The Shorter-Lived Form
MK-4 is a short-chain menaquinone found in small amounts in animal products such as egg yolks, grass-fed butter, and liver. While it is the predominant form of vitamin K2 found in the body's tissues, its bioavailability from nutritional-level supplementation is very poor. Studies show that supplemental MK-4 is rapidly cleared from the bloodstream, with a half-life of only a few hours. As a result, maintaining consistent levels requires very large, frequent doses. Therapeutic doses for bone health typically involve taking 45 mg daily, divided into three doses. This high-dose approach is often challenging for daily compliance and is significantly different from nutritional supplementation. The MK-4 found in tissues is often believed to be converted from other forms of vitamin K, including MK-7.
MK-7: The Bioavailable, Long-Lasting Form
MK-7 is a long-chain menaquinone produced by bacterial fermentation, most notably found in the traditional Japanese food natto. In contrast to MK-4, MK-7 is highly bioavailable and has a much longer half-life, staying in the bloodstream for up to 72 hours. This extended presence allows for a much smaller, once-daily dose to achieve and maintain stable serum levels, efficiently activating the vitamin K-dependent proteins needed for bone and cardiovascular health. MK-7 is particularly effective at activating matrix Gla protein (MGP), which helps prevent arterial calcification, and osteocalcin, which directs calcium to the bones. Many experts consider MK-7 to be the superior choice for general supplementation due to its long-lasting and efficient action.
The MK-4 vs. MK-7 Comparison
| Feature | MK-4 | MK-7 | Why it Matters |
|---|---|---|---|
| Source | Animal products (eggs, liver, dairy) | Fermented foods (natto, cheese) | Both are fat-soluble but come from different dietary sources. |
| Bioavailability | Poor at nutritional doses. | High, well-absorbed. | Poor bioavailability means supplements won't raise blood levels effectively. |
| Half-Life | Very short (6-8 hours). | Long (up to 72 hours or more). | Longer half-life ensures stable, consistent blood levels. |
| Dosing Frequency | Multiple doses per day required for therapeutic effect. | Once-daily dosing is sufficient. | MK-7 is far more convenient and increases compliance. |
| Therapeutic Dose | Milligram range (e.g., 45 mg daily). | Microgram range (e.g., 90-180 mcg daily). | MK-7 is effective at significantly lower, safer doses. |
| Bone Health | Strong evidence for high-dose regimens (45mg/day) improving bone density and reducing fractures. | Evidence shows it helps maintain bone quality and inhibit bone loss at nutritional doses. | MK-7 is more practical for everyday bone health maintenance. |
| Cardiovascular Health | Indirect benefits through conversion from MK-7. | Strong evidence for reducing arterial calcification and stiffness. | MK-7's long half-life allows it to be more active in extrahepatic tissues. |
| Tissue Distribution | Concentrates in specific tissues like the brain, kidneys, and reproductive organs. | Circulates widely, delivering K2 throughout the body. | MK-7 is a better 'supplier' for the body's conversion needs. |
The Synergy of a Combination Supplement
Given the distinct properties of MK-4 and MK-7, some experts and supplement manufacturers recommend a combined approach. A combination supplement can provide the convenience and systemic availability of MK-7 while leveraging the more immediate, tissue-specific uptake associated with MK-4. The body can also convert MK-7 into MK-4 where needed, but a combined supplement can ensure optimal levels of both for their respective functions. When choosing a combination product, it's vital to ensure it specifies high-quality, 'all-trans' isomers of K2, as these are the most bioactive forms. Improper processing can lead to less effective 'cis' isomers being included.
Making Your Choice
For most individuals seeking general cardiovascular and bone health support, the high bioavailability and convenience of MK-7 make it the superior choice. Its long half-life means a single, low dose is sufficient to maintain steady blood levels and activate the critical proteins that govern calcium distribution. However, individuals targeting specific, clinically-studied bone density improvements may consider the high-dose MK-4 protocol, though it requires multiple daily doses and has less evidence at nutritional levels. For those seeking the most comprehensive approach, a combination supplement containing both forms may offer the best of both worlds. Regardless of the form, always choose a high-quality product from a reputable brand and consult a healthcare provider, especially if you are taking blood-thinning medications.
Quality and Safety Considerations
Beyond the choice between MK-4 and MK-7, supplement quality is paramount. Seek brands that specify the use of 'all-trans' isomers, which are the most bioactive form of K2, often found in supplements derived from natural fermentation. Look for supplements that use microencapsulation technology to protect the vitamin, especially when combined with minerals like calcium or magnesium, as unprotected K2 can degrade rapidly. For those on warfarin or other anticoagulants, any change in vitamin K intake can be dangerous. These individuals should only start a supplement under strict medical supervision and with regular monitoring. Discover more insights into the roles of Vitamin K1 and K2.
Conclusion
While both MK-4 and MK-7 are important forms of vitamin K2, the long-lasting, highly bioavailable nature of MK-7 makes it the better choice for most people's supplementation needs. MK-7 offers a practical, once-daily dose that effectively supports cardiovascular and bone health by ensuring stable activation of key calcium-regulating proteins throughout the body. While MK-4 has specific, high-dose applications, its poor absorption at nutritional levels makes it less practical for general use. A combination supplement can offer a synergistic blend of both forms, but ultimately, MK-7 stands out for its convenience and proven efficacy in a standard daily dose.
