What are phylloquinone (Vitamin K1) and menaquinone (Vitamin K2)?
Vitamin K is not a single vitamin but a group of fat-soluble compounds with similar chemical structures. The two primary forms found in the human diet are vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). The structural differences between them lead to different absorption rates and transport mechanisms within the body, which, in turn, influence their unique functions.
Vitamin K1: Phylloquinone
Phylloquinone is the form of vitamin K found in plants, particularly in leafy green vegetables. It is the most common form of vitamin K in the average diet, making up 75–90% of a person's total vitamin K intake.
- Key function: The body uses phylloquinone primarily to activate proteins in the liver that are essential for blood clotting. Without enough vitamin K1, the blood's ability to coagulate is impaired, which can lead to excessive bleeding.
- Absorption and transport: Phylloquinone is poorly absorbed from plant sources and is quickly used by the liver. It has a much shorter half-life in the blood than menaquinone.
Vitamin K2: Menaquinone
Menaquinone, or vitamin K2, is a group of compounds (called menaquinones or MKs) that are primarily synthesized by bacteria. It is found in animal products and fermented foods. Menaquinone-4 (MK-4) is found in animal tissues and is created in the body from vitamin K1, while long-chain menaquinones like MK-7 are common in fermented foods.
- Key functions: Menaquinone is more readily available to extra-hepatic tissues, such as bones and blood vessels. It plays a crucial role in directing calcium to the bones and preventing its accumulation in the arteries.
- Bioavailability: Some forms of menaquinone, especially MK-7, are better absorbed and have a longer half-life, meaning they remain in the circulation for days.
Sources of Vitamin K1 and K2
Increasing intake of both forms of vitamin K is vital for optimizing their respective health benefits. Here are the most common dietary sources:
- Vitamin K1 (Phylloquinone):
- Leafy greens: Kale, spinach, collard greens, Swiss chard
- Vegetables: Broccoli, Brussels sprouts, cabbage, asparagus
- Some fruits: Kiwi, blueberries, grapes
- Vitamin K2 (Menaquinone):
- Fermented foods: Natto (fermented soybeans, especially rich in MK-7), sauerkraut
- Dairy: Certain hard cheeses (Gouda, Edam), soft cheeses (Brie), butter
- Animal products: Egg yolks, organ meats (chicken liver), fatty meats
Comparison of Vitamin K1 and K2
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) |
|---|---|---|
| Other Names | Phytonadione | Menaquinone (MK-4, MK-7, etc.) |
| Primary Source | Green leafy plants | Animal products and fermented foods |
| Primary Function | Blood clotting factors produced in the liver | Extra-hepatic functions; bone and cardiovascular health |
| Absorption | Poorly absorbed from plant sources | Better absorbed, especially with fat-containing foods |
| Circulation | Shorter half-life, cleared from blood in hours | Longer half-life, can circulate for days |
| Main Target Tissue | Liver | Bones and arterial walls |
The importance of adequate vitamin K intake
While vitamin K deficiency is rare in healthy adults, ensuring sufficient intake of both K1 and K2 is important for comprehensive health benefits. Beyond its established role in blood clotting, vitamin K is critical for other physiological processes. For instance, it activates specific proteins that regulate calcium utilization in the body.
Inadequate vitamin K can lead to the formation of undercarboxylated proteins, which are biologically inactive and can have adverse health consequences. This can impact bone mineralization, increasing the risk of osteoporosis and fractures. Furthermore, a lack of active proteins can contribute to arterial calcification, where calcium accumulates in the walls of blood vessels.
Research has increasingly focused on the unique benefits of vitamin K2. Studies suggest that higher vitamin K2 intake, particularly from fermented foods, is associated with a reduced risk of coronary heart disease and improved vascular elasticity. It is more bioavailable for extra-hepatic tissues, which allows it to have a more pronounced impact on bone and heart health. This highlights the importance of incorporating a variety of sources to cover the spectrum of vitamin K’s functions. For instance, the long-chain MK-7 found in natto is particularly effective for extra-hepatic functions, while K1 is critical for liver-based coagulation factors.
It is always recommended to obtain nutrients from a balanced diet first, but supplements can be considered under a healthcare provider's guidance, especially for individuals with malabsorption issues or specific health concerns. Those on blood-thinning medications like warfarin must consult a doctor, as vitamin K intake affects the medication's effectiveness.
Conclusion
In conclusion, the two main forms of vitamin K, phylloquinone (K1) and menaquinone (K2), are vital fat-soluble nutrients with distinct roles and sources. K1, predominantly from leafy greens, is essential for liver-produced blood clotting factors. K2, found in fermented foods and animal products, has a longer half-life and is more bioavailable for extra-hepatic tissues, supporting bone health and inhibiting arterial calcification. While deficiency is uncommon, focusing on a varied diet rich in both plant-based and fermented/animal-based sources ensures the body has adequate vitamin K to support everything from healthy blood coagulation to robust bone and cardiovascular function.
