Vitamin K was originally discovered in 1935 by Danish biochemist Henrik Dam and was named the "koagulation vitamin" due to its role in blood clotting. However, the term "vitamin K" actually refers to a family of fat-soluble compounds, not a single substance. The two main naturally occurring forms are phylloquinone (K1) and a group of menaquinones (K2), with different sources and functions within the body. A balanced diet should include both forms to maximize their health benefits.
The Many Monikers of Vitamin K
While vitamin K is the commonly used term, its different forms have distinct alternative names that reflect their origin and chemical structure. Knowing these names can help when identifying sources in your diet or on supplement labels.
The Plant-Based Name: Phylloquinone (Vitamin K1)
- Phylloquinone is the primary name for vitamin K1, which is synthesized by plants.
- Phytonadione is another name, often used for the synthetic form of vitamin K1 found in supplements.
- Methylphytyl naphthoquinone is a more specific chemical name that describes its molecular composition.
Phylloquinone is most concentrated in green, leafy vegetables, where it plays a critical role in the plant's photosynthesis process. In the human body, it is predominantly active in the liver and is vital for producing the proteins required for blood coagulation.
The Bacterial Name: Menaquinones (Vitamin K2)
- Menaquinone is the general name for vitamin K2, which is produced by bacteria in the human gut and found in fermented foods and animal products.
- MK-n is a notation for the different subtypes of menaquinones, where 'n' represents the number of repeating isoprenoid units in the side chain. Examples include MK-4, MK-7, and MK-9.
- Menatetrenone is the chemical name for MK-4, a form converted from phylloquinone in extrahepatic tissues like the testes, pancreas, and arterial walls.
Menaquinones, particularly MK-4 and MK-7, are known for their benefits related to bone mineralization and cardiovascular health by activating specific proteins in extra-hepatic tissues.
The Synthetic Name: Menadione (Vitamin K3)
- Menadione is a synthetic form of vitamin K that is water-soluble.
- It was previously used in supplements but is no longer available for human consumption due to its toxicity, which can damage liver cells and cause hemolytic anemia.
The Critical Role of Vitamin K in the Body
Beyond its various names, vitamin K plays two critical roles in human health:
- Blood Coagulation: Vitamin K is a co-factor for an enzyme called gamma-glutamyl carboxylase, which modifies proteins that enable them to bind to calcium. This process is essential for the function of several blood clotting factors produced in the liver (factors II, VII, IX, and X). Without sufficient vitamin K, blood clotting is impaired, leading to excessive bleeding and bruising.
- Bone Health: The vitamin is also crucial for synthesizing proteins involved in bone metabolism, such as osteocalcin. Vitamin K-dependent carboxylation of osteocalcin allows it to bind calcium, which is vital for bone mineralization and structure. A deficiency can lead to lower bone mineral density and an increased risk of fractures.
- Cardiovascular Health: A specific vitamin K-dependent protein, Matrix Gla Protein (MGP), is thought to help prevent the calcification of arteries and other soft tissues. This function is particularly associated with vitamin K2, and adequate intake may reduce the risk of cardiovascular disease.
Dietary Sources for a Vitamin K-Rich Nutrition Diet
Incorporating a variety of foods from both animal and plant sources is the best way to ensure adequate vitamin K intake. Here are some excellent dietary sources for each form:
- Vitamin K1 (Phylloquinone) Sources:
- Green leafy vegetables: Kale, spinach, collard greens, turnip greens, and Swiss chard.
- Vegetables: Broccoli, Brussels sprouts, cabbage, and cauliflower.
- Oils: Soybean oil and canola oil.
- Vitamin K2 (Menaquinones) Sources:
- Fermented foods: Natto (fermented soybeans) is an exceptionally rich source of MK-7. Sauerkraut also contains menaquinones.
- Dairy: Hard cheeses like gouda and cheddar.
- Meats: Eggs, beef, chicken, and liver.
Comparing Vitamin K1 and Vitamin K2
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinones) |
|---|---|---|
| Primary Source | Plants, especially leafy green vegetables | Bacteria (including gut bacteria), fermented foods, and animal products |
| Role in the Body | Acts mainly in the liver to activate proteins for blood clotting | Active in extra-hepatic tissues like bones and blood vessels for bone and cardiovascular health |
| Subtypes | Primarily one form (K1) | A group of subtypes (e.g., MK-4, MK-7) based on side-chain length |
| Absorption | Less efficiently absorbed from plants than K2 from food | More readily absorbed from dietary sources than K1 |
| Storage | Primarily accumulates in the liver | Found in higher concentrations in the brain, kidneys, and other tissues |
What Happens During a Vitamin K Deficiency?
Though rare in healthy adults, a vitamin K deficiency can occur under certain circumstances. A severe deficiency can cause significant bleeding and hemorrhage, a primary concern, especially in newborns who have limited vitamin K reserves at birth. Adults with malabsorption disorders (e.g., cystic fibrosis, celiac disease) or those on long-term broad-spectrum antibiotics may also be at risk. Poor bone development and reduced bone mineral density have also been linked to insufficient vitamin K levels.
Drug Interactions with Vitamin K
Vitamin K is known to interact with certain medications, most notably blood-thinning anticoagulants like warfarin. Warfarin works by interfering with the vitamin K cycle, which depletes the active form of vitamin K needed for clotting factor production. For this reason, individuals on warfarin therapy must maintain a consistent intake of vitamin K from food and supplements, as sudden changes can increase or decrease the drug's effectiveness and lead to dangerous bleeding or clotting.
Conclusion: Embracing Vitamin K in Your Healthy Diet
Ultimately, the answer to "What is another name for vitamin K?" is not a single word but a recognition that it represents a family of fat-soluble compounds, namely phylloquinone (K1) and menaquinones (K2). While K1 is crucial for blood clotting, K2 offers distinct benefits for bone and cardiovascular health. By including a diverse range of vitamin K-rich foods in your diet, from leafy greens to fermented dairy and natto, you can ensure your body receives this essential nutrient in its various forms. For more detailed information on dietary intake, resources like the National Institutes of Health provide comprehensive fact sheets (National Institutes of Health, ODS Vitamin K Fact Sheet, ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/).
