Vitamin K: What It Does and the Best Sources

Vitamin K, also known as phytomenadione, is a group derived from 2-methyl-naphthoquinones. They are human vitamins, lipophilic (soluble in lipids) and hydrophobic (insoluble in water), mainly required in blood coagulation processes. But it is also used to generate red blood cells. Intestinal bacteria normally produce Vitamin K2 (menaquinone), and dietary deficiency is extremely rare, except when an intestinal injury occurs or the vitamin is not absorbed.

It was discovered in 1935 by the Danish biochemist and physiologist Henrik Dam when trying to cure some chickens that died in a short time of serious hemorrhagic disease; it is, therefore, essential for coagulation. Three forms are known: Natural, phylloquinone present in green plants, menaquinone produced in the intestinal flora, and the synthetic compound menadione, with greater power than the other 2. The latter is fat-soluble (diluted in fat), and the previous two are also obtained in a soluble form (hydrophilic, diluted in water). Although Dr. Dam isolated it from alfalfa, it is currently synthesized in the laboratory and earned its discoverer the Nobel Prize in Medicine in 1943.

Phylloquinone (also known as Vitamin K1) invariably contains four isoprenoid residues in its side chain, one of which is unsaturated. Menaquinones have a side chain composed of a variable number of unsaturated isoprenoid residues, generally designated MK-n, where n specifies the number of isoprenoids. It is generally accepted that naphthoquinone is the functional group, so the mechanism of action is similar for all forms of this vitamin. Substantial differences can be expected, however, concerning intestinal absorption, transport, distribution to tissues, and bioavailability. These differences are caused by the different affinities for side-chain lipids and by the various food matrices in which they occur.

Vitamin K acts as an enzyme cofactor. That is, it accompanies an enzyme to fulfill its function in the body. This enzyme, called gamma-glutamyl carboxylase, facilitates the initiation of a series of chemical reactions of interest to our body. These reactions are involved in:

1. Wound Coagulation: Vitamin K is essential in the blood clotting process. Explained in a simplified way, we could say that coagulation consists of a series of chemical reactions that, when a blood vessel breaks, “cover” that break and prevent death from bleeding. Many of these chemical reactions depend on vitamin K to activate. And why are they “activated”? Well, because the proteins that participate in these reactions are “in reserve,” waiting for a wound to occur, to clot the blood; if the coagulation reactions were always to occur, the blood would clot inside us, closing the passage of liquid blood to the tissues.

Coagulation must also be limited in space. Uncontrolled, clotting would start at the site of the bleeding and continue inward, clotting much more blood than necessary. This is avoided with another series of chemical reactions, in which vitamin K is also involved. We can say then that this vitamin is essential both for starting and stopping clotting reactions.

2. Calcification of Tissues: Vitamin K also participates in the metabolism of calcium and bone. For example, and also simplifying a lot, it participates in the following processes:

• Control of calcification and hardening of blood vessels
• Activating osteocalcin, a protein that is synthesized in bones and has a certain relationship with calcium, bone structure, and energy metabolism through its interaction with insulin.
• Promoting the correct structure of the bone and its post-fracture repair

These processes are not as well known as coagulation, so a clear correlation between the lack of vitamin K and calcium metabolism, bone metabolism, or even energy metabolism has not yet been described.

3. Less known reactions of Metabolic and Vascular Functioning in the nervous system or platelets, among others.

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Vitamin K deficiency has several causes:

• Medications: the most frequent cause of hypovitaminosis K is the administration of drugs with anticoagulant activity, such as Acenocoumarol and Warfarin. These are coumarin derivatives that resemble vitamin K and compete with it for absorption but cannot convert clotting molecules to their active form in the liver. On the other hand, certain antibiotics, such as cephalosporins, can reduce the hepatic gamma-carboxylation of clotting factors since they inhibit the recycling of the vitamin.

• Liver Disease: coagulation factors may not be synthesized due to alteration of the hepatocyte, which does not metabolize vitamin K.

• Lack of Contribution: nutritional deficiency is rare since the needs are minimal. Typically, for there to be a deficiency of vitamin K, other situations tend to appear, such as psychiatric conditions, elderly patients, eating disorders, or alcoholism.

• Hemorrhagic Neonatal Disease: it is a condition that appears between two and five days of life and is characterized by ecchymosis, bruising, mucosal bleeding, and bleeding from the umbilical cord. The most common is in newborns subjected to breastfeeding since the concentration of vitamin K is lower. 

• Decreased Absorption: in malabsorption syndrome caused by alteration of the intestinal wall, celiac disease, or large intestinal resections, vitamin K may not be absorbed. Also, the existence of biliary fistulas, obstructive jaundice, intrahepatic cholestasis, and treatment with cholestyramine lead to the reduction of bile salts, favoring a low absorption of fat-soluble vitamins, including vitamin K.

Clinically, vitamin K deficiency is manifested by the disease-causing deficiency’s clinical features (anticoagulation, gallstones, etc.) and by occasionally profuse diffuse skin hemorrhage. In more serious situations, bruises and subcutaneous and muscular hematomas may appear, together with mucosal hemorrhages.

According to the United States, the reference dietary intake considered adequate for an adult man of vitamin K is 120 micrograms/day. Maximum tolerable levels have not been determined. The human body stores Vitamin K, so it is not necessary to supplement it daily. Vitamin K is found in dark green leafy vegetables, such as spinach and lettuce. Other food sources are kale, cauliflower, broccoli, Brussels sprouts, avocado, wheat germ, organic foods, cereals, some fruits, such as kiwi, bananas, meats, cow’s milk, and products such as eggs and soy products. Two tablespoons of parsley contain 153% of the recommended amount of Vitamin K. Olive oil has a significant amount of Vitamin K. Phylloquinone (Vitamin K1) is the major dietary form of the vitamin. It is also found in the yolk of chicken eggs, butter, most cheeses, and in some types of mayonnaise.