The Vitamin K Family: Distinguishing K1 and K2
Vitamin K is a family of fat-soluble compounds, known as naphthoquinones, that are essential for many bodily functions. Within this family, the two most prominent natural forms are vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). While they share some functions, their dietary sources, absorption, and primary roles differ significantly, and they should be considered distinct nutrients.
Vitamin K1, produced by plants, is the most common dietary source of vitamin K, found in high concentrations in leafy green vegetables like kale, spinach, and broccoli. Its main function is activating proteins in the liver responsible for blood clotting. The body absorbs K1 less efficiently and it has a shorter half-life, meaning it doesn't circulate in the body as long as K2.
Menaquinone: The Various Forms of Vitamin K2
What is another name for vitamin K2? The scientific name for the family of compounds collectively known as vitamin K2 is menaquinone. Menaquinones are produced by bacteria and exist in several subtypes, labeled MK-4 through MK-13, based on the length of their chemical side chain. The most researched forms are MK-4 and MK-7, each with different primary sources.
- MK-4: Found primarily in animal-based foods such as egg yolks, butter, and organ meats like beef liver. MK-4 is unique because it can also be converted from vitamin K1 within animal tissues. It has a shorter half-life than MK-7 but plays an important role in brain and bone health.
- MK-7: Richly available in fermented foods, particularly the traditional Japanese dish natto (fermented soybeans). MK-7 boasts a much longer half-life than MK-4 and K1, allowing it to be more bioavailable for extrahepatic tissues like bones and blood vessel walls.
The Health Benefits of Menaquinone
While vitamin K1 is focused on blood clotting, vitamin K2's benefits extend to extra-hepatic tissues, giving it a more diverse range of functions, particularly for long-term health.
Bone Health Vitamin K2 is a key regulator of calcium, promoting its proper integration into bone tissue. It does this by activating a protein called osteocalcin, which binds calcium to the bone matrix. Studies, particularly in Japan where natto consumption is high, show that increased K2 intake can reduce the risk of bone fractures and improve bone mineral density.
Heart Health Another critical role of menaquinone is preventing the dangerous buildup of calcium in soft tissues, especially the arteries. It activates matrix Gla protein (MGP), which inhibits calcium deposits from forming in arterial walls. This mechanism is believed to significantly reduce the risk of heart disease, with some studies suggesting a 50% lower risk of dying from heart disease in individuals with higher K2 intake.
Synergy with Vitamin D Vitamin K2 works in synergy with vitamin D. While vitamin D improves calcium absorption, K2 ensures that this absorbed calcium is directed towards bones rather than accumulating in soft tissues, amplifying their combined benefits for skeletal and cardiovascular health.
Key Dietary Sources of Menaquinone
Unlike K1, which is abundant in plants, menaquinone is found in specific fermented and animal products. Incorporating these foods can help ensure adequate K2 intake.
- Fermented foods: Natto is a powerhouse of MK-7 due to the fermentation process with specific bacteria. Sauerkraut also contains notable amounts.
- Dairy products: Hard and soft cheeses, particularly Gouda and Brie, contain menaquinones. The K2 content varies depending on the fermentation and animal diet.
- Animal products: Egg yolks, especially from pastured hens, are a good source of MK-4. Chicken, beef, and organ meats like liver also provide this form of vitamin K2.
Comparison of Vitamin K1 (Phylloquinone) vs. Vitamin K2 (Menaquinone)
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Primary Source | Plants (leafy greens) | Fermented foods & animal products |
| Body Production | Converted to MK-4 in animal tissues | Synthesized by gut bacteria |
| Primary Function | Blood clotting in the liver | Bone and heart health (extra-hepatic) |
| Subtypes | One form | Multiple forms (MK-4, MK-7, etc.) |
| Bioavailability | Lower absorption, shorter half-life | Longer half-life, better bioavailability for extra-hepatic tissues |
Conclusion: Integrating Menaquinone into a Balanced Diet
It is clear that menaquinone, or vitamin K2, plays a role in health that is distinct from its better-known cousin, phylloquinone. From strengthening bones to protecting against arterial calcification, its benefits are far-reaching. While dietary intake is the primary source, especially from foods like natto, cheese, and egg yolks, supplements are also available in forms like MK-4 and MK-7. For most healthy individuals, a balanced diet rich in both K1 and K2 is sufficient, but those on specific medications like blood thinners should consult a healthcare provider before making significant dietary changes or taking supplements. The growing body of research highlights menaquinone as a nutrient worth paying attention to for long-term well-being.
For more detailed information, the National Institutes of Health provides comprehensive factsheets on vitamin K.
