The Foundation of Vitamin K2 and Arterial Health
Vitamin K is a fat-soluble vitamin essential for several bodily functions, including blood clotting and calcium metabolism. It exists in two primary forms: K1 (phylloquinone), found mainly in leafy green vegetables, and K2 (menaquinone), found in animal products and fermented foods. Vitamin K2 plays a critical role in directing calcium to where it belongs (bones) and away from where it doesn't (arteries and soft tissues). It does this by activating Matrix Gla Protein (MGP), a potent inhibitor of arterial calcification. When MGP is not activated by vitamin K, it cannot prevent calcium infiltration, leading to arterial stiffness and calcification, a key risk factor for cardiovascular disease. However, not all forms of vitamin K2 are created equal, and the differences between MK-4 and MK-7 are particularly important for arterial health.
Menaquinone-4 (MK-4): The Short-Lived Form
Menaquinone-4 (MK-4) is a short-chain form of vitamin K2 and is the predominant form found in the human body and animal products such as eggs, meat, and liver. All forms of vitamin K can be converted to MK-4 in the body, suggesting it may have unique biological functions. However, its efficacy as a supplement for arterial health is limited by two main factors: bioavailability and half-life.
- Poor Bioavailability: Studies show that nutritional doses of MK-4 are poorly absorbed and do not significantly raise serum vitamin K2 levels.
- Short Half-Life: MK-4 is quickly cleared from the bloodstream, with a half-life of only a few hours. This means it is not consistently available to extra-hepatic tissues like arteries, requiring frequent and much higher doses to have a measurable effect on protein activation outside the liver.
- High Dose Requirement: To achieve therapeutic effects on protein carboxylation, MK-4 must be taken in pharmaceutical-level doses, often in milligrams, multiple times per day.
Menaquinone-7 (MK-7): The Bioavailable Form
Menaquinone-7 (MK-7) is a long-chain form of vitamin K2, produced by bacteria, and found primarily in fermented foods like the traditional Japanese dish natto. It is widely recognized for its superior bioavailability and longer presence in the bloodstream compared to MK-4.
- High Bioavailability: MK-7 is well absorbed from dietary and supplement sources, significantly increasing serum vitamin K2 levels.
- Long Half-Life: With a half-life of approximately 72 hours (three days), MK-7 remains in circulation far longer than MK-4. This allows it to reach and effectively activate vitamin K-dependent proteins in extra-hepatic tissues, including the arteries.
- Lower Dose Efficacy: Because of its prolonged half-life, MK-7 is effective at much lower, microgram-level doses, often requiring only a once-daily intake.
Comparing MK-4 and MK-7
| Feature | MK-4 | MK-7 |
|---|---|---|
| Half-Life | Very short (a few hours) | Long (approximately 72 hours) |
| Bioavailability | Poor at nutritional doses | High and well-absorbed |
| Source | Animal products (eggs, meat, liver) | Fermented foods (natto) and some cheeses |
| Dosing for Efficacy | High, milligram doses required multiple times daily | Low, microgram doses effective with once-daily intake |
| Arterial Target Access | Limited due to rapid clearance | Excellent due to prolonged circulation |
| Primary Role | Tissue-specific functions, but MK-7 is a better supplier for tissue levels | Systemic activation of vitamin K-dependent proteins |
Clinical Evidence and Implications for Arterial Health
Clinical research further clarifies the distinct roles of MK-4 and MK-7 in cardiovascular health. The longer presence of MK-7 in the circulation makes it a more effective candidate for targeting arterial calcification.
- MK-7 Studies: A landmark human trial involving postmenopausal women showed that supplementation with 180 mcg/day of MK-7 significantly improved measures of arterial stiffness over three years compared to a placebo. This study also observed a reduction in inactive MGP, indicating a positive effect on calcification prevention. Other studies have shown MK-7 can slow down the progression of coronary artery calcification, especially in high-risk individuals.
- MK-4 Studies: While high-dose MK-4 has been used to treat osteoporosis, particularly in Japan, its effect on arterial health at typical nutritional doses is less clear and less extensively studied than MK-7. Its rapid clearance makes it less suited for systemic benefits required to address calcification throughout the arterial system.
Conclusion
While both MK-4 and MK-7 are forms of vitamin K2 that contribute to activating proteins vital for bone and arterial health, their differences in bioavailability and half-life lead to vastly different efficacies. For the specific purpose of targeting and inhibiting arterial calcification, MK-7 is the more effective choice at nutritional doses. Its longer-lasting presence in the bloodstream allows for more consistent activation of key proteins like MGP, which helps to keep arteries flexible and prevent the accumulation of calcium. For individuals concerned about arterial health, prioritizing a diet rich in MK-7 from fermented foods like natto or choosing a supplement containing the MK-7 form is a more practical and effective approach than relying on nutritional doses of MK-4.
For more in-depth scientific information on the differences between these forms, a comprehensive review can be found in the International Journal of Molecular Sciences.
