The Two Natural Forms of Vitamin K
Vitamin K is a family of fat-soluble compounds, not a single substance, and the natural name for it depends on its specific form. The two main naturally occurring types are Vitamin K1 and Vitamin K2. Each form is distinct, with different sources, metabolic functions, and potential health benefits. While they share a core chemical structure, the variations in their side chains significantly affect their biological activity and how the body uses them.
Phylloquinone (Vitamin K1)
Phylloquinone is the natural name for Vitamin K1 and is the form found primarily in plants. As an essential electron carrier in photosynthesis, it is abundant in green leafy vegetables, including spinach, kale, and collard greens. For humans, phylloquinone is the major dietary source of vitamin K and is absorbed in the small intestine. It is most well-known for its crucial role in activating liver proteins responsible for blood coagulation, a process that prevents excessive bleeding.
Menaquinones (Vitamin K2)
Menaquinones are the natural names for the family of compounds known as Vitamin K2. Unlike phylloquinone, menaquinones are mainly produced by bacteria and are found in fermented foods and some animal products. Different types of menaquinones exist, designated MK-4 through MK-13 based on their side-chain length. For example, the subtype MK-7 is found in high concentrations in natto, a traditional Japanese fermented soybean dish, while MK-4 is found in animal-based foods like meat, eggs, and dairy. Menaquinones are particularly important for delivering vitamin K to extra-hepatic tissues, such as bones and blood vessel walls, where they support bone health and prevent arterial calcification.
Comparison of Phylloquinone vs. Menaquinone
Understanding the differences between the two natural forms of vitamin K is essential for optimizing intake for specific health goals. Here is a comparison of their key attributes:
| Feature | Phylloquinone (Vitamin K1) | Menaquinone (Vitamin K2) |
|---|---|---|
| Natural Name | Phylloquinone (or Phytonadione, a synthetic form) | Menaquinones (subtypes like MK-4, MK-7) |
| Primary Source | Green leafy vegetables, plant oils (e.g., soybean oil, canola oil) | Fermented foods (natto, some cheeses), animal products (meat, eggs) |
| Source Type | Plant-based | Bacteria-produced and animal-based |
| Primary Function | Activating liver clotting factors | Supporting bone metabolism and preventing vascular calcification |
| Absorption Site | Primarily absorbed in the small intestine | Absorbed in the small intestine, with longer-chain forms having better extra-hepatic availability |
| Tissue Distribution | Concentrated in the liver | Better bioavailability for extra-hepatic tissues like bone and arteries |
The Role of Each Natural Name in Health
Each natural form of vitamin K plays a specialized role in maintaining health. The distinct functionalities of phylloquinone and menaquinone mean that a balanced intake from a variety of sources is beneficial.
Blood Coagulation: This is the classic function associated with vitamin K, and it is overwhelmingly carried out by phylloquinone. Phylloquinone acts as a cofactor for the enzyme gamma-glutamyl carboxylase, which modifies clotting factors produced in the liver. Without sufficient phylloquinone, the liver cannot produce these clotting factors correctly, leading to an increased risk of bleeding disorders.
Bone Metabolism: While phylloquinone is involved, menaquinones, particularly MK-4 and MK-7, are believed to have a more significant impact on bone health. They help activate proteins like osteocalcin, which bind calcium to the bone matrix, promoting strong and mineralized bones. This is why research has explored high-dose menaquinone-4 as a treatment for osteoporosis in some regions.
Cardiovascular Health: Inadequate vitamin K status is associated with increased vascular calcification, a major risk factor for heart disease. This hardening of the arteries is inhibited by Matrix Gla protein (MGP), another vitamin K-dependent protein. Studies show that menaquinones, particularly longer-chain types like MK-7, are more effective at reaching and activating MGP in arterial walls, helping to prevent calcium buildup and maintain arterial elasticity.
Conclusion
To fully answer the question, "What is the natural name for vitamin K?", one must acknowledge its dual nature. The natural names for vitamin K are phylloquinone for the plant-based variant (K1) and menaquinone for the bacteria-produced variant (K2). While both are essential, they are not interchangeable, performing different but complementary functions within the body. The phylloquinone from leafy greens is crucial for blood clotting, whereas the menaquinone found in fermented and animal foods supports bone and heart health. A comprehensive understanding of these distinct forms allows individuals to make more informed dietary choices to support their overall well-being. For additional scientific information, the Office of Dietary Supplements at the National Institutes of Health provides an extensive resource on vitamin K.
