Vitamin K (K from "Koagulations-Vitamin" in German and Scandinavian languages) denotes a group of lipophilic, hydrophobic vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation. Chemically they are 2-methyl-1 derivatives.
Vitamin K1 is also known as phylloquinone or phytomenadione (also called phytonadione). Vitamin K2 (menaquinone, menatetrenone) is normally produced by bacteria in the large intestine, and dietary deficiency is extremely rare unless the intestines are heavily damaged, are unable to absorb the molecule, or due to decreased production by normal flora, as seen in broad spectrum antibiotic use.
There are three synthetic forms of vitamin K, vitamins K3, K4, and K5, which are used in many areas including the pet food industry (vitamin K3) and to inhibit fungal growth (vitamin K5).
The U.S. Dietary Reference Intake (DRI) for an Adequate Intake (AI) of Vitamin K for a 25-year old male is 120 micrograms/day. The Adequate Intake (AI) of this phytonutrient for adult women is 90 micrograms/day, for infants is 10–20 micrograms/day, for children and adolescents 15–100 micrograms/day. In 2002 it was found that to get maximum carboxylation of osteocalcin, one may have to take up to 1000 μg of Vitamin K1. Like other liposoluble vitamins (A, D, E), vitamin K is stored in the fat tissue of the human body.
Although allergic reaction from supplementation is possible, there is no known toxicity associated with high doses of the phylloquinone (vitamin K1) or menaquinone (vitamin K2) forms of vitamin K and therefore no Tolerable Upper Intake Level (UL) has been set.
However, a synthetic form of vitamin K, vitamin K3 (menadione), is demonstrably toxic. In fact, the FDA has banned this synthetic form of the vitamin from over-the-counter supplements because large doses have been shown to cause allergic reactions, hemolytic anemia, and cytotoxicity in liver cells.
Menaquinone (K2) is capable of blocking the blood thinning action of anticoagulants like warfarin, which work by interfering with the action of Vitamin K1. It also reverses the tendency of these drugs to cause arterial calcification in the long term.
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