Unveiling the Names Behind the Nutrient
While the simple label "vitamin K" is common, this nutrient is not a single compound but a family of chemically similar fat-soluble substances known as naphthoquinones. The two most important and well-known forms found in the human diet are vitamin K1 and vitamin K2, each with its own scientific name and primary sources. A third synthetic form, vitamin K3 (menadione), is no longer used in human nutrition due to potential toxicity.
Vitamin K1: Phylloquinone
Vitamin K1 is known scientifically as phylloquinone. It is the most common form of vitamin K found in the diet and is essential for the body's primary blood-clotting mechanisms.
- Origin: Produced by plants, especially those involved in photosynthesis.
- Main function: It acts as a cofactor for an enzyme responsible for activating proteins involved in the coagulation cascade, such as factors II (prothrombin), VII, IX, and X.
- Primary food sources: Found predominantly in green leafy vegetables. This form is best absorbed when consumed with a source of dietary fat.
Vitamin K2: Menaquinones
Known collectively as menaquinones, vitamin K2 actually comprises a number of subtypes, designated as MK-4 through MK-13, based on the length of their side chain. This form of vitamin K has gained significant attention for its distinct health benefits, particularly concerning bone and cardiovascular health.
- Origin: Produced by bacteria, including the microbes that reside in the human gut. Also found in certain animal products and fermented foods.
- Main function: Crucial for activating osteocalcin, a protein that directs calcium to the bones, and matrix Gla protein (MGP), which prevents calcium from accumulating in soft tissues like arteries.
- Primary food sources: Found in fermented foods like natto, as well as meat, eggs, and certain cheeses.
Vitamin K3: A Synthetic Form
Menadione, or vitamin K3, is a synthetic, water-soluble form of vitamin K. While it was once used for supplementation, it is no longer recommended for human consumption due to demonstrated toxicity in laboratory studies.
The Role of Vitamin K in the Body
Beyond its differing names, vitamin K plays a series of vital roles that impact overall health. Its functions are largely mediated through its action as a coenzyme, which is necessary for activating specific proteins throughout the body.
Key functions of vitamin K:
- Blood Coagulation: The most recognized function, as its name suggests, is enabling blood to clot. Without sufficient vitamin K, the synthesis of clotting factors in the liver would be impaired, leading to a risk of excessive bleeding.
- Bone Metabolism: Vitamin K helps maintain strong bones. It activates osteocalcin, a protein that plays a key role in integrating calcium into the bone matrix, improving density and reducing fracture risk.
- Cardiovascular Health: It supports heart health by activating matrix Gla protein (MGP). MGP inhibits calcium from building up in the arteries, which can lead to cardiovascular disease.
Comparison of Key Vitamin K Forms
| Feature | Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinones) |
|---|---|---|
| Primary Source | Plant-based foods (e.g., leafy greens, vegetable oils) | Bacteria, fermented foods, animal products |
| Best Known For | Blood clotting | Bone and heart health |
| Absorption | Absorbed less efficiently than K2, especially without fat | Higher absorption rates, longer half-life in the body |
| Bioavailability | Lower bioavailability compared to certain forms of K2 | Higher bioavailability, especially longer-chain forms like MK-7 |
| Primary Action Site | Primarily in the liver | Extrahepatic tissues (bones, arteries, pancreas) |
Symptoms of Vitamin K Deficiency
While rare in healthy adults, vitamin K deficiency can be a serious concern, especially in infants. A deficiency leads to an impaired ability to clot blood, causing a range of bleeding symptoms.
Common symptoms include:
- Easy bruising and excessive bleeding from wounds.
- Oozing from the nose or gums.
- Blood in the urine or stool, or dark, tarry stools.
- Heavy menstrual bleeding.
Newborns are at a higher risk of deficiency, which can cause life-threatening bleeding into the brain; for this reason, they routinely receive a vitamin K injection at birth. Certain health conditions affecting absorption, chronic antibiotic use, or taking blood-thinning medications can also increase risk.
Getting Your Daily Intake
The amount of vitamin K you need varies by age and sex. For adults, the Adequate Intake (AI) is set at 120 mcg for men and 90 mcg for women. A varied and balanced diet that includes a good mix of green leafy vegetables and other sources is usually sufficient for meeting this requirement.
To ensure a healthy intake, you can focus on consuming a diverse range of vitamin K-rich foods. For more details on daily requirements, the NIH Office of Dietary Supplements provides a comprehensive resource: Vitamin K - NIH Office of Dietary Supplements.
Conclusion
To answer the question, "what is vitamin K called?", we must recognize its various forms. While commonly referred to as vitamin K, its primary compounds are phylloquinone (K1) and menaquinones (K2). Phylloquinone, found in plants, is essential for blood clotting, while menaquinones, from fermented foods and bacteria, are critical for bone and heart health. Understanding these different names and functions is key to appreciating this nutrient's comprehensive impact on human health, from preventing excessive bleeding to maintaining strong bones and healthy arteries.
Essential Facts on Vitamin K
- The name 'Vitamin K' refers to a group: It's not a single substance but a family of related fat-soluble compounds.
- Two main forms are K1 and K2: Phylloquinone (K1) comes from plants, and menaquinone (K2) from bacteria and fermented foods.
- K1 is for clotting: Vitamin K1's primary function is its critical role in producing blood-clotting proteins in the liver.
- K2 supports bones and heart: Vitamin K2 is vital for activating proteins that build bone and prevent arterial calcification.
- Deficiency can cause bleeding: The most common symptom of deficiency is excessive bleeding, which can be life-threatening in newborns.
- Foods are the best source: The daily vitamin K requirement can be met by eating a balanced diet rich in leafy greens, fermented foods, and certain animal products.
- Supplements have different forms: Supplements can contain either K1 (phytonadione) or various forms of K2 (e.g., MK-4, MK-7), with K2 showing greater bioavailability.
- Synthetic K3 is toxic: Menadione (vitamin K3) is a synthetic form that is not used for human nutrition due to safety concerns.
