Vitamin K

Vitamin K is a group of 2-methilo-naphthoquinone derivatives. There are three notable forms of vitamin K, K1 (phytonadione, phylloquinone, phytonactone), K2 (menaquinones), which can be formed by natural bacteria in the intestines, and K3 (menadione), the most active synthetic form of the preparations K3-K7. Plants synthesize phylloquinone, also known as vitamin K1. Vitamin K1 or phylloquinone is the principal dietary source of vitamin K and its predominant circulating form. Vitamin K2 is the collective term for a group of vitamin K compounds called menaquinones.

The menaquinone homolgues are characterized by the number of isoprene residues comprising the side chain. Vitamin K2 is found in chicken egg yolk, butter, cow liver, certain cheeses and fermented soybean products such as natto. Very little vitamin K is stored by the body; small amounts of this vitamin are deposited in the liver and in the bones, but this amount is only enough to supply the body's needs for a few days.

Vitamin K is involved in the carboxylation of certain glutamate residues in proteins to form gamma-carboxyglutamate residues. These proteins have in common the requirement to be post-translationally modified by carboxylation of glutamic acid residues (forming gamma-carboxyglutamic acid) in order to become biologically active. These proteins include the vitamin K-dependent coagulation factors II (prothrombin), VII (proconvertin), IX (Christmas factor), X (Stuart factor), protein C, protein S, protein Zv and a growth-arrest-specific factor (Gas6). Menadione is a fat-soluble vitamin precursor that is converted into menaquinone in the liver. The primary known function of vitamin K is to assist in the normal clotting of blood, but it may also play a role in normal bone calcificaton. Without vitamin K, the carboxylation does not occur and the proteins that are synthesized are biologically inactive.

Vitamin K functions, uses, and health benefits

Vitamin K plays an important role in blood clotting and bone metabolism (carboxylation of osteocalcin). High serum concentrations of undercarboxylated osteocalcin and low serum concentrations of vitamin K are associated with lower bone mineral density and increased risk of hip fracture. Vitamin K supplements may improve bone mass in postmenopausal women. Vitamin K prevents calcification of arteries and other soft tissue. Calcification of organs and other soft tissue is an adverse consequence of aging. Vitamin K may play a role in the regulation of blood sugar. The pancreas, which makes insulin, has the second highest amount of vitamin K in the body.

Vitamin K and blood clotting

Vitamin K's primary function is to regulate normal blood clotting (due to its role in the synthesis of prothrombin). 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. Vitamin K regulates normal blood clotting by helping the body transport calcium. Protein Z appears to enhance the action of thrombin (the activated form of prothrombin) by promoting its association with phospholipids in cell membranes. Protein C and protein S are anticoagulant proteins that provide control and balance in the coagulation cascade. Vitamin K2, not vitamin K1 (phylloquinone; phytonadione), may improve a group of blood disorders known as myelodysplastic syndromes.

Vitamin K and bone health

Vitamin K supplements improve bone health and reduce risk of bone fractures, particularly in postmenopausal women who are at risk for osteoporosis. Three vitamin-K dependent proteins have been isolated in bone. Higher vitamin K levels correspond to greater bone density, while low levels of vitamin K have been found in those with osteoporosis. In bones, vitamin K mediates the gamma-carboxylation of glutamyl residues on several bone proteins, notably osteocalcin. Osteocalcin is a protein synthesized by osteoblasts (bone forming cells). The mineral-binding capacity of osteocalcin requires vitamin K-dependent gamma-carboxylation of three glutamic acid residues.

Vitamin K and liver diseases

Vitamin K is used to reduce risk of bleeding in liver disease, jaundice, malabsorption, or in association with long-term use of aspirin or antibiotics. Gastrointestinal problems that decrease the absorption of vitamin K, such as obstructions in the bile duct, cystic fibrosis, sprue, Crohn's disease, colitis and medications that reduce the absorption of this vitamin, such as antibiotics. Vitamin K deficiency in those with cystic fibrosis is worsened by their recurrent need for antibiotics. Vitamin K has been used in the treatment of heavy menstrual bleeding, and with vitamin C to treat morning sickness. Newborns are at risk for bleeding in the brain because of the trauma of coming through the birth canal during delivery.

Vitamin K dosage, intake, recommended daily allowance (RDA)

The recommended dietary allowance (RDA) for vitamin K is 120 mcg per day for adult males and 90 mcg per day for adult females, and about 2 mcg/day for the newborn infant. Natural forms of vitamin K found in foods are only about half as potent compared to synthetic version. While adequate amount of vitamin K can be obtained by consuming leafy green vegetables on a regular basis for many men and women between 18 and 44 years may benefit from supplemental vitamin K.

Sources of vitamin K

Rich sources of vitamin K include broccoli, Brussels sprouts, cabbage, cauliflower, kale, spinach and soybeans. Cooked dark green vegetables, such as spinach, kale and broccoli, can provide more than one RDA in a single serving. Cow milk is also a good source of the vitamin. Asian soy foods also are excellent vitamin K sources. Hydrogenation of vegetable oils may decrease the absorption and biological effect of dietary vitamin K. Phylloquinone (vitamin K1) is the major dietary form of vitamin K. Bacteria that normally colonize the large intestine synthesize menaquinones (vitamin K2), which are an active form of vitamin K.

Many forms of vitamin K are available (synthetic and natural). It is found in multivitamin formulas and in 5-mg tablet form.

Water-soluble chlorophyll is most common and available without a prescription. The natural forms of vitamin K that are found in many foods, particularly in vegetables such as collard greens, spinach, broccoli, asparagus, brussels sprouts and salad greens, are a different form – they are called phylloquinone or menaquinone. Certain bacteria in the intestinal tract also produce menaquinones. Good sources of vitamin K are the dark, leafy, green vegetables including spinach and broccoli high amounts are also found in olive, canola and soybean oils cabbage, carrots, avocados, cucumbers, and tomatoes all have a significant amount of vitamin K in them dairy products such as yogurt are reasonable sources, and meats and cereals also contain some vitamin K.

Leafy green vegetables, such as spinach, kale, collards, and broccoli, are the best sources of vitamin K. The greener the plant, the higher the vitamin K content. 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. Soybean oil, canola oil, and olive oil are good sources of the vitamin, while corn oil and peanut oil are very poor sources. In animal-source foods, K is found in liver, milk, yogurt, egg yolks, and fish liver oils. The best source for humans is that made by the intestinal bacteria.

Vitamin K deficiency

Vitamin K deficiency is very rare and occurs when there is an inability to absorb the vitamin from the intestinal tract. Vitamin K deficiency can also occur after prolonged treatment with oral antibiotics. Vitamin K deficiency is often the result of impaired absorption rather than not getting enough in the diet. Prolonged use of antibiotics can also cause a low level of this vitamin because they destroy some of the bacteria in the gut that help to produce vitamin K.

Newborns are at risk for vitamin K deficiency. This is because their digestive tracts contain no vitamin K-producing bacteria. Vitamin K deficiency in adults is rare. When it occurs, it is found in people with diseases that prevent the absorption of fat. These diseases include cystic fibrosis, celiac disease, and cholestasis. Symptoms of vitamin K deficiency include easy bruisability, epistaxis, gastrointestinal bleeding, menorrhagia and hematuria.

Vitamin K is a fat-soluble vitamin that plays an important role in blood clotting. Vitamin K is known as the clotting vitamin, because without it blood would not clot. 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. Vitamin K is involved as a cofactor in the posttranslational gamma-carboxylation of glutamic acid residues of certain proteins in the body. 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 is very rare and occurs when there is an inability to absorb the vitamin from the intestinal tract. Vitamin K deficiency can also occur after prolonged treatment with oral antibiotics. Individuals with vitamin K deficiency usually have an increased propensity to bruising and bleeding. Deficiency can occur in persons of any age but neonates are at risk of developing haemorrhagic disease of the newborn. This is because of a lack of vitamin K reaching the foetus across the placenta, the low level of vitamin K in breast milk and low colonic bacterial synthesis.

In adults, vitamin K deficiency is uncommon. In infants, vitamin K deficiency without bleeding may occur in as many as 50% of infants younger than 5 days old. The classic haemorrhagic disease occurs in 0.25-1.7% of infants. The prevalence of late haemorrhagic disease in breast-fed infants is about 20 per 100,000 live births with no prior prophylaxis with Vitamin K.

Vitamin K deficiency can occur under certain conditions including inadequate dietary intake, malabsorption syndromes (cystic fibrosis, Crohn's disease, ulcerative colitis, Whipple's disease, celiac sprue, short bowel syndrome) and loss of storage sites due to hepatocellular disease. Vitamin K deficiency frequently occurs in those with chronic liver disease, such as primary biliary cirrhosis.

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. Newborns are especially prone to vitamin K deficiency. A nursing-mother's milk is low in the vitamin; breast milk can supply only about 20% of the infant's requirement. Infants are born with low levels of vitamin K in their body; they do not have any vitamin K-producing bacteria in their intestines. Their digestive tracts are sterile. As a result, a form of vitamin K deficiency, called hemorrhagic disease of the newborn, may develop. This disease involves spontaneous bleeding beneath the skin or elsewhere in the infant's body, and occurs in about 1% of all infants.

In rare cases, it causes death due to spontaneous bleeding in the brain. Vitamin K deficiency in adults is rare. When it occurs, it is found in people with diseases that prevent the absorption of fat. These diseases include cystic fibrosis, celiac disease, and cholestasis. Vitamin K deficiency can exist in adults treated with antibiotics that kill the bacteria that normally live in the digestive tract. As mentioned, the intestine-bacteria supply part of our daily requirement of vitamin K. Vitamin K deficiency can result in bleeding gums, and in skin that is easily bruised.

Many of the popular rodenticides act by inducing a vitamin K deficiency which, if severe, leads to death by bleeding. Coumarin derivatives such as Warfarin and dicumarol interfere with recycling of vitamin K (see above) and thereby lead to vitamin K deficiency. The liver synthesizes bile acids and secretes them into the small intestine where they play a critical role in absorption of lipids. Vitamin K, as a fat-soluble vitamin, requires proper lipid absorption for its own absorption. Liver disease that results in decreased bile salt synthesis leads to impaired vitamin K absorption and deficiency. Vitamin K is a nutrient found in the small intestine where it combines with protein to produce clotting of the blood.

Certain cases of vitamin K deficiency have resulted in a failure of the clotting process and in hemorrhages. In particular, there is a danger that hemorrhages may occur in the brains of newborns who lack sufficient vitamin K. Symptoms of vitamin K deficiency include easy bruisability, epistaxis, gastrointestinal bleeding, menorrhagia and hematuria. Chronic vitamin K deficiency may also result in osteoporosis and increased risk of fractures. There is some evidence that chronic warfarin use may also cause osteoporosis.