The Essentials of Vitamin K2
Vitamin K is a fat-soluble nutrient, with two primary forms: vitamin K1 (phylloquinone), found mostly in leafy green vegetables, and vitamin K2 (menaquinone), found in fermented and animal-based foods. Vitamin K2 is further broken down into subtypes called menaquinones (MK-n), based on the length of their side chain. While MK-4 and MK-7 are the most studied, their absorption and effectiveness within the body vary dramatically. For individuals focused on bone and cardiovascular health, understanding these differences is key to optimizing dietary intake and supplementation.
MK-7 vs. MK-4: Unpacking the Bioavailability
Bioavailability refers to the proportion of a nutrient that is absorbed and utilized by the body. For vitamin K2, the differences in bioavailability between MK-4 and MK-7 are substantial, with research consistently demonstrating MK-7's superiority at typical nutritional dosages.
The Critical Role of Half-Life
One of the most significant factors influencing absorption and utilization is the nutrient's half-life, which refers to how long it remains active in the bloodstream. MK-7 has a notably long half-life of approximately 72 hours, meaning it stays in circulation for an extended period. In contrast, MK-4 has a very short half-life, lasting only a few hours before being rapidly cleared from the body. This prolonged presence of MK-7 allows for stable, consistent levels in the blood, ensuring tissues can continually draw upon it.
Tissue Distribution and Accumulation
The longer half-life of MK-7 directly translates to better distribution and accumulation in extrahepatic tissues—areas outside the liver—including bones and arterial walls. The liver primarily retains vitamin K1 and, to a large extent, MK-4 for its blood clotting functions. However, long-chain menaquinones like MK-7 are efficiently redistributed from the liver and circulate longer, reaching vital tissues where they activate specific proteins crucial for health. Studies confirm that nutritional doses of MK-7 increase serum levels significantly, whereas similar doses of MK-4 do not.
Comparing MK-7 and MK-4
| Feature | Menaquinone-7 (MK-7) | Menaquinone-4 (MK-4) |
|---|---|---|
| Half-Life | Long (~72 hours) | Short (several hours) |
| Bioavailability | High, accumulates in serum | Poor at nutritional doses, quickly cleared |
| Tissue Distribution | Extensively distributed to extrahepatic tissues | Primarily used by the liver for clotting |
| Required Dose | Low, microgram doses effective | High, milligram doses potentially needed |
| Primary Source | Fermented foods like natto | Animal products like meat and eggs |
| Dosing Frequency | Once per day | Multiple times per day for efficacy |
Sources of Highly Absorbable Vitamin K2
For those seeking a highly absorbable form of vitamin K2, there are both dietary and supplemental options, primarily focusing on MK-7.
- Natto: This traditional Japanese dish of fermented soybeans is by far the richest dietary source of MK-7. It provides a very high concentration of MK-7 in a single serving.
- Hard Cheeses: Certain fermented cheeses, particularly hard cheeses like Gouda, contain moderate amounts of MK-7 and other long-chain menaquinones.
- Supplements: Due to the rarity of natto in many Western diets, MK-7 supplements are a popular and practical option. They often contain a specific, patented form of MK-7, such as MenaQ7®, which is well-researched for its cardiovascular and bone health benefits.
Benefits of Optimal K2 Absorption
Ensuring you get the most absorbable form of vitamin K2 is crucial for maximizing its health benefits, which extend beyond simple blood clotting. Vitamin K2 activates proteins that play a significant role in where calcium is deposited in the body.
Bone Health
For strong bones, vitamin K2 activates osteocalcin, a protein produced by bone-building cells. Activated osteocalcin effectively binds calcium and integrates it into the bone matrix, improving bone mineral density and strength. MK-7, with its superior bioavailability, provides a steady supply of vitamin K2 to bone tissue for this process.
Cardiovascular Health
Vitamin K2 also protects cardiovascular health by activating Matrix Gla Protein (MGP), which prevents the calcification of soft tissues like arteries. By directing calcium away from arteries and into bones, MK-7 helps maintain arterial elasticity and reduces the risk of plaque buildup.
Conclusion: The Case for MK-7
While both MK-4 and MK-7 are forms of vitamin K2, the evidence clearly shows that MK-7 is the more absorbable and effective choice, particularly at nutritional doses for systemic health benefits. Its longer half-life and superior ability to accumulate in extrahepatic tissues make it the optimal form for supporting bone mineralization and protecting against arterial calcification. For most people, a combination of MK-7-rich foods like natto or a high-quality MK-7 supplement is the most efficient way to ensure adequate vitamin K2 intake for long-term health.
For more detailed scientific comparisons, a review article in the International Journal of Molecular Sciences provides further insight into the differences between vitamin K1 and K2.
