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vitamin K

 
Medical Encyclopedia: Vitamin K Deficiency
 
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Definition

Vitamin K deficiency exists when chronic failure to eat sufficient amounts of vitamin K results in a tendency for spontaneous bleeding or in prolonged and excessive bleeding with trauma or injury. Vitamin K deficiency occurs also in newborn infants, as well as in people treated with certain antibiotics. The protein in the body most affected by vitamin K deficiency is a blood-clotting protein called prothrombin.

Description

Vitamin K is a fat-soluble vitamin. The recommended dietary allowance (RDA) for vitamin K is 80 mg/day for the adult man, 65 mg/day for the adult woman, and 5 mg/day for the newborn infant. The vitamin K present in plant foods is called phylloquinone; while the form of the vitamin present in animal foods is called menaquinone. Both of these vitamins are absorbed from the diet and converted to an active form called dihydrovitamin K.

Spinach, lettuce, broccoli, brussels sprouts, and cabbage are good sources of vitamin K, containing about 8 mg vitamin K/kg food. Cow milk is also a good source of the vitamin.

A portion of the body's vitamin K is supplied by bacteria living in the intestine rather than by dietary sources.

Vitamin K plays an important role in blood clotting. Without the vitamin, even a small cut would cause continuous bleeding in the body, and death. Blood clotting is a process that begins automatically when any injury produces a tear in a blood vessel. The process of blood clotting involves a collection of molecules, which circulate continuously through the bloodstream. When an injury occurs, these molecules rapidly assemble and form the blood clot. The clotting factors are proteins, and include proteins called Factor II, Factor VII, Factor IX, and Factor X. Factor II is also called prothrombin. These proteins require vitamin K for their synthesis in the body. The blood-clotting process also requires a dozen other proteins that do not need vitamin K for their synthesis.

— Tom Brody, PhD


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Dictionary: vitamin K
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n.

A fat-soluble vitamin, occurring in leafy green vegetables, tomatoes, and egg yolks, that promotes blood clotting and prevents hemorrhaging. It exists in several related forms, such as K1 and K2.


 
Sci-Tech Encyclopedia: Vitamin K
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A group of compounds derived from 2-methyl-1,4-naphthoquinone that prevent bleeding in mammals and birds. Vitamin K1 (phylloquinone) is produced by green plants; a related form, vitamin K2 (menaquinone), is produced by intestinal bacteria. Chemically synthesized forms include vitamin K1, K2, and menadione (vitamin K3). All of these compounds are fat-soluble liquids at room temperature that become biologically inactive when exposed to light or alkali. See also Vitamin.

Vitamin K1 (phylloquinone) is a photosynthesis cofactor in plants, and various forms of vitamin K2 (menaquinones) participate in energy transfer reactions in bacteria. Mammals and many other animals need vitamin K hydroquinone (the active form) as a cofactor for the specific synthesis of the amino acid γ-carboxyglutamate (Gla) in certain proteins, which enable the proteins to bind calcium and phospholipids with high specificity. Gla is an essential part of coagulation factors and of other proteins that regulate blood clotting (hence the disruption of blood clotting and internal bleeding associated with vitamin K deficiency). See also Amino acids; Blood; Coenzyme; Protein.

Humans depend on continuous vitamin K supplies, since storage is minimal. Good dietary sources of vitamin K1 are green vegetables and fruits; certain fermented Asian foods, especially natto, have a high vitamin K2 content.

Intestinal bacteria produce vitamin K2, and under most circumstances enough is absorbed to prevent bleeding. However, spontaneous bleeding occurs if both dietary intake and production by intestinal bacteria are persistently low. Other health risks related to inadequate vitamin K intake may include accelerated loss of bone minerals and hardening of arteries.

 
Food and Nutrition: vitamin K
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Fat-soluble vitamin essential for the synthesis of γ-carboxyglutamate in prothrombin and other proteins involved in the blood clotting system, and bone proteins. Deficiency causes impaired blood coagulation and haemorrhage. Two groups of compounds have vitamin K activity: phylloquinones, found in green plants, and a variety of menaquinones synthesized by intestinal bacteria. Dietary deficiency is unknown, except when associated with general malabsorption diseases. However, some new-born infants are at risk of haemorrhage as a result of low vitamin K status, and it is general practice to give a single, relatively large dose of the vitamin shortly after birth.

 
Food and Fitness: vitamin K
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anti-haemorrhagic vitamin

A fat-soluble vitamin which occurs in two main forms: one of plant origin (phyto-menadione or phylloquinone), and the other of animal origin (menaquinone). Dietary sources include green leafy vegetables, some vegetable oils, and liver. Some vitamin K is derived from bacterial activity in the gut, but it is not clear how active this form of vitamin K is compared with phylloquinone. Bacterial synthesis is not adequate to maintain normal blood clotting if no phylloquinone is obtained from the diet. Vitamin K is needed to manufacture prothrombin, a substance essential for the normal clotting of blood. Deficiency is rare but may result from taking antibiotics which interfere with the activity of gut bacteria. Symptoms include easy bruising and prolonged clotting time, leading to excessive bleeding and haemorrhage.

 
Dental Dictionary: vitamin K
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n

(phytonadione, anti-hemorrhagic factor), one of the many fat-soluble naphthoquinone compounds with vitamin D activity. Vitamin K1 is found primarily in leafy vegetables, K2 is synthesized by human intestinal bacteria, and K3 (menadione, N.F.) is a synthetic compound. Vitamin K is essential for the synthesis of prothrombin by the liver. A dietary deficiency of vitamin K is rare, however. The vitamin has been used in conjunction with extensive oral antibiotic therapy to treat hemorrhagic disease of the newborn, hemorrhage of obstructive jaundice, and sprue, and during anticoagulant therapy. Prothrombin, Stuart factor, Christmas factor, and serum prothrombin conversion accelerator require vitamin K for their synthesis.

 
Drug Info: Phytonadione, Vitamin K1
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Brand names: AquaMEPHYTON®, Mephyton®

Chemical formula:



Phytonadione, Vitamin K1 tablets

What are phytonadione tablets?

PHYTONADIONE (Mephyton®) is a man-made form of vitamin K. Vitamin K is found naturally in foods such as green, leafy vegetables, soybeans, and meats, especially liver. Phytonadione treats vitamin K deficiency or bleeding problems caused by various disorders. Generic phytonadione tablets are not yet available.

What should I tell my health care provider before I take this medicine?

They need to know if you have any of these conditions:
• liver disease
• an unusual or allergic reaction to phytonadione, other medicine, foods, dyes, or preservatives
• pregnant or trying to get pregnant
• breast-feeding

How should I take this medicine?

Take phytonadione tablets by mouth. Follow the directions on the prescription label. Swallow the tablets with a drink of water. Take your doses at regular intervals. Do not take your medicine more often than directed.

What if I miss a dose?

If you miss a dose, take it as soon as you can. If it is almost time for your next dose, take only that dose. Do not take double or extra doses.

What drug(s) may interact with phytonadione tablets?

• cholestyramine
• colestipol
• mineral oil
• orlistat
• warfarin

Tell your prescriber or health care professional: about all other medicines you are taking including non-prescription medicines; if you are a frequent user of drinks with caffeine or alcohol; if you smoke; or if you use illegal drugs. These can affect the way your medicine works. Check with your health care professional before stopping or starting any of your medicines.

What should I watch for while taking phytonadione tablets?

Visit your prescriber or health care professional for regular checks on your progress. Your prescriber or health care professional will schedule tests to make sure the medicine is working properly. Do not take more phytonadione than prescribed.

If you are going to have surgery, tell your prescriber or health care professional that you are taking phytonadione.

What side effects might I notice from taking phytonadione tablets?

Side effects that you should report to your prescriber or health care professional as soon as possible:
• changes in taste
• flushing of the face

Where can I keep my medicine?

Keep out of the reach of children in a container that small children cannot open.

Store at room temperature between 15—30 degrees C (59—86 degrees F). Protect from light. Store in tightly closed container and original carton until contents have been used. Throw away any unused medicine after the expiration date.

Last updated: 7/1/2002

Important Disclaimer: The drug information provided here is for educational purposes only. It is intended to supplement, not substitute for, the diagnosis, treatment and advice of a medical professional. This drug information does not cover all possible uses, precautions, side effects and interactions. It should not be construed to indicate that this or any drug is safe for you. Consult your medical professional for guidance before using any prescription or over the counter drugs.

 
Alternative Medicine Encyclopedia: Vitamin K
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Description

Vitamin K originates from the German term koajulation. It is also known as antihemorrhagic factor, and is one of the four fat-soluble vitamins necessary for good health. The others are vitamins A, D, and E. The primary and best-known purpose of vitamin K is support of the process of blood clotting. Prothrombin and other clotting factors are dependent on vitamin K for production. It also plays a role in bone health, and may help to prevent osteoporosis. Appropriate growth and development are supported by adequate vitamin K.

There are several forms of the vitamin:

  • K1 or phylloquinone; also known as phytonadione
  • K2, a family of substances called menaquinones
  • K3 or menadione, a synthetic form of this vitamin

General Use

The Required Daily Amount (RDA) of vitamin K is 5 micrograms (mcg) for infants less than six months old, 10 mcg for babies six months to one year old, 15 mcg for children aged one to three years, 20 mcg for those aged four to six years, and 30 mcg for those seven to ten years old. Males require 45 mcg from 11–14 years, 65 mcg from 15–18 years, 70 mcg from 19–24 years, and 80 mcg after the age of 24 years. Females need 45 mcg from 11–14 years, 55 mcg from 15–18 years, 60 mcg from 19–24 years, and 65 mcg after the age of 24, and for pregnant or lactating women. These values are based on an estimate of 1 mcg of vitamin K per kilogram of body weight.

The most common use of vitamin K is to supplement babies at birth, thus preventing hemorrhagic disease of the newborn. Routine administration of vitamin K to newborns is, however, being questioned by practitioners of evidence-based nursing. In 2003 the American Academy of Pediatrics (AAP) restated that prevention of bleeding from early vitamin K deficiency by administration of the vitamin is accepted practice. The AAP also noted that a possible link between supplemental vitamin K and early childhood cancer has not been proven as of 2003.

Others who may benefit from supplemental vitamin K include those taking medications that interact with it or deplete the supply. It also appears to have some effectiveness in preventing osteoporosis, but some studies done involved patients using a high dietary intake of the vitamin rather than supplements. In 2003, however, a group of Japanese researchers reported that supplemental doses of vitamin K2 given together with vitamin D3 appeared to reduce bone turnover and sustain bone density in postmenopausal women with mild osteoporosis.

People taking warfarin, a vitamin K antagonist, are able to use the vitamin as an antidote if the serum level of warfarin is too high, increasing the risk of hemorrhage. Vitamin K taken by mouth appears to be more effective than intramuscular injections of the vitamin when it is used to counteract the effects of warfarin.

Vitamin K is also used to treat bleeding from the esophagus and other complications of cirrhosis, a disease of the liver.

Some women find that supplemental vitamin K relieves the symptoms of morning sickness during pregnancy. This treatment is even more effective if vitamin K is taken together with vitamin C.

Topical formulations of vitamin K are sometimes touted as being able to reduce spider veins on the face and legs. The creams are quite expensive and the efficacy is questionable at best. However, recent clinical studies have shown that topical applications of vitamin K given to patients following laser treatments on the face are effective in minimizing bruising from the procedure.

More recently, researchers have been studying vitamin K intensively for its potential anticancer effects. Vitamin K3 in particular may be useful as an adjuvant treatment for ovarian cancer.

Preparations

Natural Sources

Dark green leafy vegetables are among the best food sources of vitamin K in the form of K1. Seaweed is packed with it, and beef liver, cauliflower, eggs, and strawberries are rich sources as well. Vitamin K is fairly heat-stable, but gentle cooking preserves the content of other nutrients that are prone to breaking down when heated. Some of the supply for the body is synthesized as vitamin K2 by the good bacteria in the intestines.

Supplemental Sources

Vitamin K is not normally included in daily multivitamins, as deficiency is rare. Oral, topical, and injectable forms are available, but should not be used except under the supervision of a health care provider. Injectable forms are by prescription only. Supplements are generally given in the form of phytonadione since it is the most effective form and has a lower risk of toxicity than other types. Synthetic forms of vitamin K are also available for supplemental use.

Deficiency

Deficiency of vitamin K is uncommon in the general population but is of particular concern in neonates, who are born with low levels of vitamin K. Hemorrhagic disease of the newborn can affect infants who do not receive some form of vitamin K at birth. Affected babies tend to have prolonged and excessive bleeding following circumcision or blood draws. In the most serious cases, bleeding into the brain may occur. Most commonly an injection of vitamin K is given in the nursery following birth, but a series of oral doses is also occasionally used. The primary sign of a deficiency at any age is bleeding, and poor growth may also be observed in children.

Chronically low levels of vitamin K are correlated with higher risk of hip fracture in older men and women. A study done in 2003 reported that the current recommended dietary intake for vitamin K in adults may not be adequate for older women.

Risk Factors for Deficiency

Vitamin K deficiency is unusual, but may occur in certain populations, including those on the medications mentioned in interactions, alcoholics, and people with diseases of the gastrointestinal tract that impair absorption. Conditions that may be problematic include Crohn's disease, chronic diarrhea, sprue, and ulcerative colitis. Anything that impairs fat absorption also risks decreasing the absorption of the fat-soluble vitamins. Long term use of broad spectrum antibiotics destroys the bacteria in the intestinal tract that are necessary for the body's production of vitamin K.

Precautions

Allergic reactions to vitamin K supplements can occur, although they are rare. Symptoms may include flushed skin, nausea, rash, and itching. Medical attention should be sought if any of these symptoms occur. Infants receiving vitamin K injections occasionally suffer hemolytic anemia or high bilirubin levels, noticeable from the yellow cast of the skin. Emergency medical treatment is needed for these babies. Liver and brain impairment are possible in severe cases.

Certain types of liver problems necessitate very cautious use of some forms of vitamin K. Menadiol sodium diphosphate, a synthetic form also known as vitamin K4, may cause problems in people with biliary fistula or obstructive jaundice. A particular metabolic disease called G6-PD deficiency also calls for careful use of vitamin K4. The expertise of a health care professional is called for under these circumstances. Sheldon Saul Hendler, MD, PhD, advises there is no reason to supplement with more than 100 mcg daily except in cases of frank vitamin K deficiency.

Side Effects

Oral forms of vitamin K4 may occasionally irritate the gastrointestinal tract. High doses greater than 500 mcg daily have been reported to cause some allergictype reactions, such as skin rashes, itching, and flushing.

Interactions

There are numerous medications that can interfere with the proper absorption or function of vitamin K. The long-term use of antacids may decrease the efficacy of the vitamin, as can certain anticoagulants. Warfarin is an anticoagulant that antagonizes vitamin K. Efficacy of the vitamin is also decreased by dactinomycin and sucralfate. Absorption is decreased by cholestyramine and colestipol, which are drugs used to lower blood cholesterol levels. Other drugs that may cause a deficiency include long-term use of mineral oil, quinidine, and sulfa drugs. Primaquine increases the risk of side effects from taking supplements.

Other types of prescription medications that may cause vitamin K depletion include anticonvulsants (drugs to prevent seizures), including valproic acid; macrolide, aminoglycoside, cephalosporin, and fluoroquinolone antibiotics; phenobarbital; and dapsone (used to treat leprosy and skin infections).

Resources

Books

Bratman, Steven, and David Kroll. Natural Health Bible. Rocklin, CA: Prima Publishing, 1999.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: The Complete Guide. AZ: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. CA: Therapeutic Research Faculty, 1999.

Pelletier, Kenneth R., MD. The Best Alternative Medicine, Part I: Food for Thought. New York: Simon & Schuster, 2002.

Pressman, Alan H., and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: Alpha Books, 1997.

Periodicals

American Academy of Pediatrics Committee on Fetus and Newborn. "Controversies Concerning Vitamin K and the Newborn. American Academy of Pediatrics Committee on Fetus and Newborn." Pediatrics 112 (July 2003) (1 Pt 1): 191–192.

Booth, S. L., L. Martini, J. W. Peterson, et al. "Dietary Phylloquinone Depletion and Repletion in Older Women." Journal of Nutrition 133 (August 2003): 2565–2569.

Crowther, M. A., J. D. Douketis, T. Schnurr, et al. "Oral Vitamin K Lowers the International Normalized Ratio More Rapidly Than Subcutaneous Vitamin K in the Treatment of Warfarin-Associated Coagulopathy. A Randomized, Controlled Trial." Annals of Internal Medicine 137 (August 20, 2002): 251-254.

Iwamoto, J., T. Takeda, and S. Ichimura. "Treatment with Vitamin D3 and/or Vitamin K2 for Postmenopausal Osteoporosis." Keio Journal of Medicine 52 (September 2003): 147–150.

Lamson, D. W., and S. M. Plaza. "The Anticancer Effects of Vitamin K." Alternative Medicine Review 8 (August 2003): 303–318.

Libby, E. N., and D. A. Garcia. "A Survey of Oral Vitamin Use by Anticoagulation Clinics." Archives of Internal Medicine 162 (September 9, 2002): 1893-1896.

Lucena, M. I., R. J. Andrade, G. Tognoni, et al. "Multicenter Hospital Study on Prescribing Patterns for Prophylaxis and Treatment of Complications of Cirrhosis." European Journal of Clinical Pharmacology 58 (September 2002): 435-440.

Medves, J. M. "Three Infant Care Interventions: Reconsidering the Evidence." Journal of Obstetric, Gynecologic, and Neonatal Nursing 31 (September-October 2002): 563-569.

Shah, N. S., M. C. Lazarus, R. Bugdodel, et al. "The Effects of Topical Vitamin K on Bruising After Laser Treatment." Journal of the American Academy of Dermatology 47 (August 2002): 241-244.

von Gruenigen, V. E., J. M. Jamison, J. Gilloteaux, et al. "The in vitro Antitumor Activity of Vitamins C and K3 Against Ovarian Carcinoma." Anticancer Research 23 (July-August 2003): 3279–3287.

Organizations

American Academy of Pediatrics (AAP). 141 Northwest Point Boulevard, Elk Grove Village, IL 60007. (847) 434-4000. .

American Society for Clinical Nutrition. 9650 Rockville Pike, Bethesda, MD 20814. (301) 530-7110. .

American Society of Hematology (ASH). 1900 M Street, NW, Suite 200, Washington, DC 20036. (202) 776-0544. .

[Article by: Judith Turner; Rebecca J. Frey, PhD]

 
Britannica Concise Encyclopedia: vitamin K
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Any of several fat-soluble compounds essential for the clotting of blood. A deficiency of vitamin K in the body leads to an increase in clotting time. In 1929 a previously unrecognized fat-soluble substance present in green leafy vegetables was found to be required for coagulation of the blood; its letter name comes from the Danish word koagulation. A pure form was isolated and analyzed structurally in 1939; several related compounds having vitamin-K activity have since been isolated and synthesized. The form of vitamin K that is important in mammalian tissue is of microbial origin. A synthetic vitamin K precursor called menadione is used as a vitamin supplement.

For more information on vitamin K, visit Britannica.com.

 
Sports Science and Medicine: vitamin K
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anti-haemorrhagic vitamin

A fat-soluble vitamin that occurs in two main forms: one of plant origin (phytomenadione), and the other of animal origin (menaquinone). Dietary sources include green leafy vegetables, some vegetable oils, and liver. About half the requirement is derived from the activities of bacteria in the gut. Vitamin K is needed to manufacture prothrombin, a substance essential for the normal clotting of blood. It is also thought to be involved in oxidative phosphorylation, the chemical reactions that release most of the energy from food during aerobic respiration. Deficiency is rare, but may result from taking antibiotics, which interfere with the activity of gut bacteria. Symptoms include easy bruising and prolonged clotting time, leading to excessive bleeding and haemorrhage.

 
Veterinary Dictionary: vitamin K
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A group of fat-soluble compounds which are required for the formation of prothrombin and therefore play a role in blood clotting. They are present in most green feeds and are not likely to be absent from natural diets. Failure to absorb the vitamin is a real risk in diseases in which fat absorption is defective, such as obstructive jaundice.

  • v. K deficiency — most commonly due to anticoagulant rodenticide poisoning in dogs, and less often cats.
  • v. K1 — phylloquinone.
  • v. K2 — menaquinone.
  • v. K3 — menadione.
 
Wikipedia: Vitamin K
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This article is about the biomolecule known as vitamin K. For the unrelated drug sometimes referred to as vitamin K, see ketamine.
Vitamin K1 (phylloquinone). Both contain a functional naphthoquinone ring and an aliphatic side chain. Phylloquinone has a phytyl side chain.
Vitamin K2 (menaquinone). In menaquinone the side chain is composed of a varying number of isoprenoid residues.

Vitamin K (K from "Koagulations-Vitamin" in German and Scandinavian languages[1]) 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-1,4-naphthoquinone 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[2], 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[3].

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) [4]

Contents

Chemical structure

All members of the vitamin K group of vitamins share a methylated naphthoquinone ring structure, and vary in the aliphatic side chain attached at the 3-position (see figure 1). Phylloquinone (also known as vitamin K1) invariably contains in its side chain four isoprenoid residues, one of which is unsaturated.

Menaquinones have side chains composed of a variable number of unsaturated isoprenoid residues; generally they are designated as MK-n, where n specifies the number of isoprenoids.

It is generally accepted that the naphthoquinone is the functional group, so that the mechanism of action is similar for all K-vitamins. Substantial differences may be expected, however, with respect to intestinal absorption, transport, tissue distribution, and bio-availability. These differences are caused by the different lipophilicity of the various side chains, and by the different food matrices in which they occur.

Physiology

Vitamin K is involved in the carboxylation of certain glutamate residues in proteins to form gamma-carboxyglutamate residues (abbreviated Gla-residues). The modified residues are often (but not always) situated within specific protein domains called Gla domains. Gla-residues are usually involved in binding calcium. The Gla-residues are essential for the biological activity of all known Gla-proteins.[5]

At this time 14 human proteins with Gla domains have been discovered, and they play key roles in the regulation of three physiological processes:

Recommended amounts

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 [vitamins A, D, E], vitamin K is stored in the fat tissue of the human body.

Toxicity

Although allergic reaction 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) have been set. However, vitamin K3 (menadione) has been shown to be toxic. In fact, the FDA has banned this synthetic form of the vitamin from over-the-counter supplements as large doses have been shown to cause allergic reactions, hemolytic anemia and cytotoxicity in liver cells. [9]

Drug Interactions

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.

Sources

Vitamin K is found chiefly in leafy green vegetables such as spinach, swiss chard, and Brassica (e.g. cabbage, kale, cauliflower, broccoli, and brussels sprouts); some fruits such as avocado and kiwifruit are also high in Vitamin K. By way of reference, two tablespoons of parsley contain 153% of the recommended daily amount of vitamin K.[10]. Some vegetable oils, notably soybean, contain vitamin K, but at levels that would require relatively large caloric consumption to meet the USDA recommended levels.[11]

It is believed that phylloquinone's tight binding to the thylakoid membranes in the chloroplasts is the reason behind the poor bioavailability of vitamin K in green plants. For example, cooked spinach has a 4 percent bioavailability of phylloquinone. However when one adds butter to the spinach, the bioavailability increases to 13 percent due to the increased solubility of vitamin K in fat. [12]

Menaquinone-4 and Menaquinone-7 (vitamin K2) are found in meat, eggs, dairy [13] and natto[14]. MK-4 is synthesized by animal tissues, the rest (mainly MK-7) are synthesized by bacteria during fermentation. In natto 0% of vitamin K is from MK-4 and in cheese 2-7%.[15]

Deficiency

Main article: Vitamin K deficiency

Average diets are usually not lacking in vitamin K and primary vitamin K deficiency is rare in healthy adults. As previously mentioned, newborn infants are at an increased risk of deficiency. Other populations with an increased prevalence of vitamin K deficiency include individuals who suffer from liver damage or disease (i.e. alcoholics), people with cystic fibrosis, inflammatory bowel diseases or those who have recently had abdominal surgeries. Groups which may suffer from secondary vitamin K deficiency include bulimics, those on stringent diets and those taking anticoagulants. Other drugs which have been associated with vitamin K deficiency include salicylates, barbiturates and cefamandole, although the mechanism is still unknown. There is no difference between the sexes as both males and females are affected equally. Symptoms of deficiency include heavy menstrual bleeding in women, anemia, bruising, and bleeding of the gums or nose .[15]

Osteoporosis [1][2] and coronary heart disease[3] [4]are strongly associated with lower levels of K2 (Menaquinone). Menaquinone is not inhibited by salicylates as happens with K1, so Menaquinone supplimentation can alleviate the chronic vitamin K deficiency caused by long term aspirin use.

Biochemistry

Discovery

In 1929, Danish scientist Henrik Dam investigated the role of cholesterol by feeding chickens a cholesterol-depleted diet.[16] After several weeks, the animals developed hemorrhages and started bleeding. These defects could not be restored by adding purified cholesterol to the diet. It appeared that—together with the cholesterol—a second compound had been extracted from the food, and this compound was called the coagulation vitamin. The new vitamin received the letter K because the initial discoveries were reported in a German journal, in which it was designated as Koagulationsvitamin. Edward Adelbert Doisy of Saint Louis University did much of the research that led to the discovery of the structure and chemical nature of Vitamin K.[17] Dam and Doisy shared the 1943 Nobel Prize for medicine for their work on Vitamin K. Several laboratories synthesized the compound in 1939.[18]

For several decades the vitamin K-deficient chick model was the only method of quantitating vitamin K in various foods: the chicks were made vitamin K-deficient and subsequently fed with known amounts of vitamin K-containing food. The extent to which blood coagulation was restored by the diet was taken as a measure for its vitamin K content. Three groups of physicians independently found this: Biochemical Institute, University of Copenhagen (Dam and Johannes Glavind), University of Iowa Department of Pathology (Emory Warner, Kenneth Brinkhous, and Harry Pratt Smith), and the Mayo Clinic (Hugh Butt, Albert Snell, and Arnold Osterberg). [19] The first published report of successful treatment with vitamin K of life-threatening hemorrhage in a jaundiced patient with prothrombin deficiency was made in 1938 by Smith, Warner, and Brinkhous.[20]

Function in the cell

The precise function of vitamin K was not discovered until 1974, when three laboratories (Stenflo et al.[21], Nelsestuen et al.[22], and Magnusson et al.[23]) isolated the vitamin K-dependent coagulation factor prothrombin (Factor II) from cows that received a high dose of a vitamin K antagonist, warfarin. It was shown that while warfarin-treated cows had a form of prothrombin that contained 10 glutamate amino acid residues near the amino terminus of this protein, the normal (untreated) cows contained 10 unusual residues which were chemically identified as gamma-carboxyglutamate, or Gla. The extra carboxyl group in Gla made clear that vitamin K plays a role in a carboxylation reaction during which Glu is converted into Gla.

The biochemistry of how Vitamin K is used to convert Glu to Gla has been elucidated over the past thirty years in academic laboratories throughout the world. Within the cell, Vitamin K undergoes electron reduction to a reduced form of Vitamin K (called Vitamin K hydroquinone) by the enzyme Vitamin K epoxide reductase (or VKOR).[24] Another enzyme then oxidizes Vitamin K hydroquinone to allow carboxylation of Glu to Gla; this enzyme is called the gamma-glutamyl carboxylase[25][26] or the Vitamin K-dependent carboxylase. The carboxylation reaction will only proceed if the carboxylase enzyme is able to oxidize Vitamin K hydroquinone to vitamin K epoxide at the same time; the carboxylation and epoxidation reactions are said to be coupled reactions. Vitamin K epoxide is then re-converted to Vitamin K by the Vitamin K epoxide reductase. These two enzymes comprise the so-called Vitamin K cycle.[27] One of the reasons why Vitamin K is rarely deficient in a human diet is because Vitamin K is continually recycled in our cells.

Warfarin and other coumarin drugs block the action of the Vitamin K epoxide reductase.[28] This results in decreased concentrations of Vitamin K and Vitamin K hydroquinone in the tissues, such that the carboxylation reaction catalyzed by the glutamyl carboxylase is inefficient. This results in the production of clotting factors with inadequate Gla. Without Gla on the amino termini of these factors, they no longer bind stably to the blood vessel endothelium and cannot activate clotting to allow formation of a clot during tissue injury. As it is impossible to predict what dose of Warfarin will give the desired degree of suppression of the clotting, Warfarin treatment must be carefully monitored to avoid over-dosing. See Warfarin.

Methods of Assessment

Prothrombin time test: Measures the time required for blood to clot: Blood sample mixed with citric acid and put in a fibrometer Delayed clot formation indicates a deficiency Unfortunately insensitive to mild deficiency as the values do not change until the concentration of prothrombin in the blood has declined by at least 50 percent [29]

Plasma Phylloquinone: Was found to be positively correlated with phylloquinone intake in elderly British women, but not men [30] However an article by Schurges et al. reported no correlation between FFQ and plasma phylloquinone [31]

Urinary γ-carboxyglutamic acid: Urinary Gla responds to changes in dietary Vitamin K intake Several days are required before any change can be observed In a study by Booth et al. increases of phylloquinone intakes from 100 ug to between 377-417 ug for 5 days did NOT induce a significant change Response may be age-specific [32]

Gla-proteins

At present, the following human Gla-containing proteins have been characterized to the level of primary structure: the blood coagulation factors II (prothrombin), VII, IX, and X, the anticoagulant proteins C and S, and the Factor X-targeting protein Z. The bone Gla-protein osteocalcin, the calcification inhibiting matrix gla protein (MGP), the cell growth regulating growth arrest specific gene 6 protein (Gas6), and the four transmembrane Gla proteins (TMGPs) the function of which is at present unknown. Gas6 can function as a growth factor that activates the Axl receptor tyrosine kinase and stimulates cell proliferation or prevents apoptosis in some cells. In all cases in which their function was known, the presence of the Gla-residues in these proteins turned out to be essential for functional activity.

Gla-proteins are known to occur in a wide variety of vertebrates: mammals, birds, reptiles, and fish. The venom of a number of Australian snakes acts by activating the human blood clotting system. Remarkably, in some cases activation is accomplished by snake Gla-containing enzymes that bind to the endothelium of human blood vessels and catalyze the conversion of procoagulant clotting factors into activated ones, leading to unwanted and potentially deadly clotting.

Another interesting class of invertebrate Gla-containing proteins is synthesized by the fish-hunting snail Conus geographus.[33] These snails produce a venom containing hundreds of neuro-active peptides, or conotoxins, which is sufficiently toxic to kill an adult human. Several of the conotoxins contain 2-5 Gla residues.[34]

Function in Bacteria

Many bacteria, such as Escherichia coli found in the large intestine, can synthesize Vitamin K2 (menaquinone),[35] but not Vitamin K1 (phylloquinone). In these bacteria, menaquinone will transfer two electrons between two different small molecules, in a process called anaerobic respiration.[36] For example, a small molecule with an excess of electrons (also called an electron donor) such as lactate, formate, or NADH, with the help of an enzyme, will pass two electrons to a menaquinone. The menaquinone, with the help of another enzyme, will in turn transfer these 2 electrons to a suitable oxidant, such fumarate or nitrate (also called an electron acceptor). Adding two electrons to fumarate or nitrate will convert the molecule to succinate or nitrite + water, respectively. Some of these reactions generate a cellular energy source, ATP, in a manner similar to eukaryotic cell aerobic respiration, except that the final electron acceptor is not molecular oxygen, but say fumarate or nitrate (In aerobic respiration, the final oxidant is molecular oxygen (O2) , which accepts four electrons from an electron donor such as NADH to be converted to water.) Escherichia coli can carry out aerobic respiration and menaquninone-mediated anaerobic respiration.

Vitamin K Injection in Newborns and Carcinogenicity

Newborn babies are also particularly at risk for vitamin K deficiency as the blood clotting factors of babies are roughly 30 to 60 percent that of adult values due to the reduced synthesis of precursor proteins and the sterility of their guts. Premature babies are at an even higher risk of this deficiency. Human milk contains between 1 and 4 micrograms/litre of vitamin K1, while formula derived milk can contain up to 100 micrograms/litre in supplemented formulas. Vitamin K2 concentrations in human milk appear to be much lower than those of vitamin K1. It is estimated that there is a 0.25 to 1.7 percent occurrence of vitamin K deficiency bleeding in the first week of the infant's life with a prevalence of 2-10 cases per 100,000 births [37]. As a result, in the Committee on Nutrition of the American Academy of Pediatrics recommended that 0.5 to 1.0 mg Vitamin K1 be administered to all newborns shortly after birth [38]. Controversy arose in the early 1990’s regarding this practice when two studies were shown suggesting a relationship between parenteral administration of vitamin K and childhood cancer (14). However poor methods and small sample sizes led to the discredit of these studies and a review of the evidence published in 2000 by Ross and Davies found no link between the two [39].

Vitamin K and Bone Health

Recently vitamin K has also been lauded for its potential role in the increase of bone mass. Studies have proved that supplemental vitamin K promotes osteotrophic processes and slows osteoclastic processes via calcium bonding. In Japan, a form of vitamin K2 is recognized as a treatment for osteoporosis [40][41]. However the long term effects and benefits are unknown and it remains controversial.[citation needed] Data from the 1998 Nurses Health Study found an inverse relationship between dietary vitamin K1 and the risk of hip fracture. After being given 110 micrograms/day of vitamin K, the main results showed that women who consumed lettuce one or more times per day had a significantly lower risk of hip fracture than women who consumed lettuce one or fewer times per week. In addition to this, high intakes of vitamin D but low intakes of vitamin K may still pose an increased risk of hip fracture hinting at a relationship between these two vitamins [Kanai, T. et al. Serum Vitamin K level and Bone Mineral Density in Postmenopausal Women. International Journal of Gynecology and Obstetrics; 1997; 56:25-30.].

Other studies have shown that Vitamin K-Antagonists lead to early calcification of the epiphysis and epiphysial line in mice and other animals, causing seriously decreased bone growth. This is due to defects on osteocalcin and matrix gla protein. Their primary function is to avoid overcalcification of the bone and cartilage. Vitamin K is important in the process of carboxylating glutamic acid (Glu) in these proteins to gamma-carboxyglutamic acid (Gla), activating the protein. [42]

Vitamin K and Alzheimer's Disease

Research into the antioxidant properties of vitamin K indicates that the concentration of vitamin K is lower in the circulation of carriers of the APOE4 gene and recent studies have shown its ability to inhibit cell death due to oxidation in nerve cells. It has been hypothesized that vitamin K may exude an effect on neuronal damage and that supplementation may hold benefits to treating this disease, although more research is necessary in this area. [43]

Vitamin K as a beauty product

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A study published in the Journal of Cosmetic Dermatology examined the effect of applying a gel containing 2% vitamin K plus 0.1% vitamin A, vitamin E, and vitamin C. Fifty-seven adults with dark circles participated in the 8-week study, in which 47% of the testers noted "fair to moderate" improvement in their dark circles. The majority of testers noticed no change, but the treatment was well-tolerated. [44]

Vitamin K and Cancer

At the same time researchers in Japan were studying the role of vitamin K2 in the prevention of bone loss in females with liver disease, they discovered another possible effect of this phytonutrient. This two year study which involved 21 women with viral liver cirrhosis found that women in the supplement group were 90 percent less likely to develop liver cancer [45][46] A German study performed on men with prostate cancer found a significant inverse relationship between vitamin K2 consumption and advanced prostate cancer [47]

Vitamin K as an Antidote for Poisoning by Coumarins

Vitamin K is a true antidote for poisoning by coumarins such as bromadiolone, which are commonly found in rodenticides. Coumarins possess anticoagulatory and rodenticidal properties because they can completely block synthesis of Vitamin K in the liver, especially in rodents. Death is usually a result of internal hemorrhage. Treatment usually consists of a large intravenous dose of Vitamin K, followed by doses in pill form for a period of at least two weeks, though usually three to four, afterwards. If caught early, prognosis is good, even when large amounts are ingested.

References

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External links

v • d • e
Vitamins (A11)
Fat soluble
K
Water soluble
v • d • e
Enzyme cofactors
Coenzymes
vitamins: NAD+ (B3) · NADP+ (B3) · Coenzyme A (B5) · THF / H4F (B9), DHF, MTHF · Ascorbic acid (C) · Menaquinone (K) · Coenzyme F420
non-vitamins: ATP · CTP · SAM · PAPS · GSH · Coenzyme B · Coenzyme M · Coenzyme Q · Methanofuran · BH4 · H4MPT
Organic prosthetic groups
vitamins: TPP / ThDP (B1) · FMN, FAD (B2) · PLP / P5P (B6) · Biotin (B7) · Methylcobalamin, Cobamamide (B12)
non-vitamins: Haem / Heme (A, B, C, O) · Lipoic acid · Molybdopterin · PQQ
Metal prosthetic groups
Ca2+ · Cu2+ · Fe2+, Fe3+ · Mg2+ · Mn2+ · Mo · Ni2+ · Se · Zn2+
Major families of biochemicals
Saccharides/Carbohydrates/Glycosides · Amino acids/Peptides/Proteins/Glycoproteins · Lipids/Terpenes/Steroids/Carotenoids · Alkaloids/Nucleobases/Nucleic acids · Cofactors/Flavonoids/Polyketides/Tetrapyrroles
v • d • e
Antihemorrhagics (B02)
Hemostatics
(coagulation)
Systemic
Vitamin K
intrinsic: IX/Nonacog alfa · VIII

extrinsic: VII/Eptacog alfa

common: X · II/Thrombin · I/Fibrinogen
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