Search Nerddpedia

Vitamin K

** Vitamin K is a family of fat‑soluble compounds essential for activating clotting factors and regulating calcium deposition in bone and other tissues. **CONTENT:** ## Overview Vitamin K refers to a group of structurally related, **fat‑soluble vitamers** that include phylloquinone (vitamin K₁) and a series of menaquinones (vitamin K₂). These compounds are present in a wide variety of foods—from leafy greens and vegetable oils to fermented dairy and certain animal products—and are also sold as dietary supplements. In the human body, vitamin K functions as a **cofactor for the enzyme gamma‑glutamyl carboxylase**, which catalyzes the post‑translational modification of specific proteins containing glutamic acid residues. This modification converts glutamic acid to **γ‑carboxyglutamic acid (Gla)**, enabling the proteins to bind calcium ions with high affinity. The resulting **Gla‑proteins** are indispensable for the coagulation cascade (e.g., factors II, VII, IX, X) and for the regulation of calcium in bone (osteocalcin) and vascular tissue (matrix Gla‑protein). Because vitamin K is fat‑soluble, its absorption depends on dietary fat and bile salts, and it is stored primarily in the liver and adipose tissue. The body recycles vitamin K through a cycle known as the **vitamin K cycle**, wherein the oxidized form (vitamin K epoxide) is reduced back to its active quinone state by the enzyme vitamin K epoxide reductase (VKOR). This recycling underlies the mechanism of action of the anticoagulant drug warfarin, which inhibits VKOR and thereby reduces the activation of clotting factors. ## History/Background The existence of a “fat‑soluble factor” required for blood clotting was first hinted at in the early 20th century when researchers observed that diets low in certain fats impaired coagulation in rats. In 1929, Danish scientist **Henrik Dam** isolated the factor from alfalfa sprouts and demonstrated that its absence caused hemorrhagic disease in chickens. Dam named the compound “**vitamin K**” (from the German *Koagulation*). For this discovery, he shared the 1943 Nobel Prize in Physiology or Medicine with Edward Adelbert Doisy, who later identified the chemical structure of phylloquinone in 1939. The subsequent discovery of menaquinones in the 1950s expanded the vitamin family, revealing that gut bacteria also synthesize vitamin K₂. Over the following decades, research clarified the vitamin K cycle, the role of gamma‑glutamyl carboxylase, and the clinical implications for anticoagulant therapy, bone health, and cardiovascular disease. ## Key Information - **Forms:** - **Vitamin K₁ (phylloquinone):** Predominantly found in green leafy vegetables (spinach, kale) and some plant oils. - **Vitamin K₂ (menaquinones):** Subdivided into MK‑4 to MK‑13 based on side‑chain length; MK‑4 is abundant in animal tissues, while longer‑chain MK‑7–MK‑9 are produced by bacterial fermentation (e.g., natto, certain cheeses). - **Dietary Recommendations:** The Institute of Medicine (now the National Academy of Medicine) sets an Adequate Intake (AI) of **90 µg/day for adult women** and **120 µg/day for adult men**. These values are based on the amount needed to maintain normal coagulation. - **Absorption & Metabolism:** Requires dietary fat and bile; absorbed via the lymphatic system. The liver stores ~10 % of body stores; the remainder circulates bound to lipoproteins. - **Physiological Roles:** - **Coagulation:** Activation of clotting factors II, VII, IX, X, and proteins C and S. - **Bone Health:** Carboxylation of osteocalcin enhances calcium binding, promoting mineralization. - **Vascular Health:** Matrix Gla‑protein inhibits calcium deposition in arterial walls; deficiency is linked to vascular calcification. - **Deficiency:** Rare in healthy adults but can occur with malabsorption (e.g., celiac disease, cystic fibrosis), prolonged antibiotic use, or use of vitamin K antagonists. Symptoms include easy bruising, prolonged bleeding, and, in severe cases, hemorrhagic disease of the newborn. - **Supplementation & Interactions:** High‑dose vitamin K supplements can counteract warfarin therapy; patients on anticoagulants must maintain consistent vitamin K intake and discuss any changes with their prescriber. **⚠️ Clinical Note:** If you suspect a vitamin K deficiency, are pregnant, have a bleeding disorder, or are taking anticoagulant medication, **consult a qualified healthcare professional** before altering your diet or starting supplements. ## Significance Vitamin K’s discovery reshaped our understanding of nutrition, hemostasis, and bone metabolism. Its dual role in clotting and calcium regulation makes it a pivotal factor in both acute medical care (e.g., reversal of warfarin‑induced bleeding) and chronic disease prevention (e.g., osteoporosis, atherosclerosis). Ongoing research explores vitamin K’s potential in reducing fracture risk, slowing vascular calcification, and even modulating inflammation and cancer pathways. Public health guidelines now emphasize adequate intake through a balanced diet rich in leafy greens and fermented foods, while clinicians monitor vitamin K status when prescribing anticoagulants. The vitamin’s unique biochemical cycle also serves as a classic model for enzyme‑cofactor interactions, influencing drug development and pharmacogenomics. **INFOBOX:** - **Name:** Vitamin K (phylloquinone & menaquinones) - **Type:** Fat‑soluble vitamin (vitamer family) - **Date:** Discovered 1929 (Nobel Prize 1943) - **Location:** Naturally occurring in plants, animal products, and produced by gut microbiota - **Known For:** Essential cofactor for γ‑carboxylation of clotting factors and calcium‑binding proteins **TAGS:** vitamin K, coagulation, bone health, fat‑soluble vitamins, nutrition, anticoagulant therapy, gamma‑glutamyl carboxylase, dietary supplements