The Different Forms of Vitamin K
Vitamin K is not a single compound but a family of fat-soluble vitamins. The various forms are chemically similar but differ in their side-chain structures, which affects their biological activity and dietary sources. The two main natural forms are vitamin K1 and vitamin K2.
Vitamin K1: Phylloquinone
Found in high concentrations in green leafy vegetables like spinach, kale, and broccoli, phylloquinone is the primary source of vitamin K in the human diet. It is also referred to by the alternative names phytonadione or phytomenadione, particularly in clinical and pharmacological settings. Its most well-known function is acting as a cofactor for the synthesis of blood clotting proteins in the liver, such as prothrombin. This is why vitamin K shots containing phytonadione are administered to newborns to prevent a serious bleeding condition.
Vitamin K2: Menaquinones (MK-n)
The second major form, vitamin K2, is a group of compounds called menaquinones, abbreviated as MK-n. These are predominantly produced by bacteria, both in fermented foods and within the human gut, though the colonic production is not believed to contribute significantly to overall vitamin K status due to poor absorption. Menaquinones differ based on the length of their isoprenoid side chains, with MK-4 and MK-7 being the most well-known. While K1 is primarily involved in liver-related blood clotting, K2 is more influential in other tissues, playing a crucial role in bone health and preventing vascular calcification.
Vitamin K3: Menadione
Historically, menadione, or vitamin K3, was used as a synthetic form of vitamin K. However, it is no longer used in human dietary supplements due to safety concerns, including potential liver toxicity. Menadione is still used in animal feeds in some contexts.
Sources of Different Vitamin K Forms
Obtaining sufficient amounts of the right type of vitamin K requires a varied diet. The sources for K1 and K2 are quite different.
- Vitamin K1 (Phylloquinone): Primarily from plants.
- Green leafy vegetables (spinach, kale, collard greens)
- Broccoli and Brussels sprouts
- Some vegetable oils, including soybean and olive oil
- Vitamin K2 (Menaquinones): Primarily from animal products and fermented foods.
- Fermented soybeans (natto) is a particularly rich source of MK-7.
- Certain cheeses and dairy products contain menaquinones.
- Organ meats, such as liver.
Vitamin K's Role Beyond Blood Clotting
While its function in blood coagulation is perhaps its most famous role, vitamin K's impact on health extends further. It acts as a cofactor for an enzyme that activates several proteins by adding a carboxyl group to glutamate residues, allowing them to bind to calcium. This mechanism is crucial for both clotting and bone mineralization. For instance, vitamin K activates osteocalcin, a protein that directs calcium toward bone, and matrix Gla protein (MGP), which prevents calcium from accumulating in soft tissues like arteries. This broader role explains why both K1 and K2 are important, as their different side-chains influence their distribution and activity in various parts of the body.
Comparison of Vitamin K1 and Vitamin K2
To better understand the differences between these two important forms, the following table provides a quick comparison.
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinones) |
|---|---|---|
| Primary Source | Green leafy vegetables, plant oils | Fermented foods, animal products, gut bacteria |
| Main Function | Liver function, blood clotting proteins | Extrahepatic functions, including bone health and soft tissue calcification prevention |
| Chemical Structure | Contains a phytyl side chain | Group of compounds (MK-n) with varying isoprenoid side chain lengths |
| Primary Storage Site | Primarily concentrated in the liver | Distributed to various extrahepatic tissues like bones and arteries |
| Bioavailability | Absorbed less efficiently from plant foods compared to K2 | Longer-chain menaquinones (e.g., MK-7) have high bioavailability and a longer half-life |
Conclusion
In summary, the alternative name for vitamin K depends on which form is being referenced. Phylloquinone is the alternative name for vitamin K1, derived from plants and crucial for blood clotting. The various forms of menaquinones (MK-n) are the alternative names for vitamin K2, which are important for bone and cardiovascular health and come from fermented foods and animal products. Recognizing that these are distinct yet related compounds is essential for a complete understanding of vitamin K's diverse roles and its importance for overall health. A balanced diet incorporating both plant-based sources of K1 and, where possible, fermented or animal sources of K2 ensures adequate intake for multiple bodily functions.
Learn more about the chemical structure and metabolic pathways of vitamin K on PubChem.
Frequently Asked Questions
Q: What is the main difference between vitamin K1 and K2? A: The main difference lies in their sources and primary functions. K1 (phylloquinone) is found in plants and is crucial for liver-based blood clotting, while K2 (menaquinones) is from fermented foods and animal products, and is more active in bone health and preventing arterial calcification.
Q: Can a person get all the vitamin K they need from green vegetables? A: While green vegetables are a primary source of vitamin K1 (phylloquinone), they do not provide significant amounts of vitamin K2 (menaquinones). To get a balance of both forms, a diverse diet that includes fermented foods or animal products is recommended.
Q: What is phytonadione? A: Phytonadione is a specific alternative name for vitamin K1 (phylloquinone) and is often used in medical and pharmacological contexts, especially for supplements or injections.
Q: Is menadione (vitamin K3) safe to take as a supplement? A: No, menadione is a synthetic form of vitamin K that was shown to cause liver cell damage in laboratory studies and is no longer used in human dietary supplements.
Q: What is the medical term for vitamin K deficiency? A: Vitamin K deficiency can lead to a condition known as hypoprothrombinemia, which impairs blood clotting and can cause excessive bleeding.
Q: Does vitamin K help with osteoporosis? A: Yes, vitamin K, particularly vitamin K2 (menaquinones), is vital for bone health because it activates osteocalcin, a protein that helps incorporate calcium into the bone matrix. Studies have shown that supplementation may improve bone mineral density.
Q: Do gut bacteria produce all the vitamin K2 a person needs? A: While gut bacteria do produce some menaquinones (K2), the amount and absorption are generally considered insufficient to meet the body's full needs, especially for extrahepatic tissues like bone.
Q: What is an antihemorrhagic factor? A: Antihemorrhagic factor is an older, alternative name for vitamin K, referencing its critical function in preventing excessive bleeding or hemorrhage.
