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Vitamin K

Vitamin K
Drug class
Class identifiers
Use Vitamin K deficiency, Warfarin overdose
ATC code B02BA
Biological target Gamma-glutamyl carboxylase
Clinical data Medical Encyclopedia
External links
MeSH D014812

Vitamin K is a group of structurally similar, fat-soluble vitamins the human body requires for complete synthesis of certain proteins that are prerequisites for blood coagulation and which the body also needs for controlling binding of calcium in bones and other tissues. The vitamin K-related modification of the proteins allows them to bind calcium ions, which they cannot do otherwise. Without vitamin K, blood coagulation is seriously impaired, and uncontrolled bleeding occurs. Low levels of vitamin K also weaken bones and promote calcification of arteries and other soft tissues.

Chemically, the vitamin K family comprises 2-methyl-1,4-naphthoquinone (3-) derivatives. Vitamin K includes two natural vitamers: vitamin K1 and vitamin K2. Vitamin K2, in turn, consists of a number of related chemical subtypes, with differing lengths of carbon side chains made of isoprenoid groups of atoms.

Vitamin K1, also known as phylloquinone, is made by plants, and is found in highest amounts in green leafy vegetables because it is directly involved in photosynthesis. It may be thought of as the "plant" form of vitamin K. It is active as a vitamin in animals and performs the classic functions of vitamin K, including its activity in the production of blood-clotting proteins. Animals may also convert it to vitamin K2.

Bacteria in the gut flora can also convert K1 into vitamin K2. In addition, bacteria typically lengthen the isoprenoid side chain of vitamin K2 to produce a range of vitamin K2 forms, most notably the MK-7 to MK-11 homologues of vitamin K2. All forms of K2 other than MK-4 can only be produced by bacteria, which use these forms in anaerobic respiration. The MK-7 and other bacterially derived forms of vitamin K2 exhibit vitamin K activity in animals, but MK-7's extra utility over MK-4, if any, is unclear and is a matter of investigation.

Food Serving size Vitamin K1 micrograms (μg) Food Serving size Vitamin K1 micrograms (μg)
Kale, cooked 1/2 cup 531 Parsley, raw 1/4 cup 246
Spinach, cooked 1/2 cup 444 Spinach, raw 1 cup 145
Collards, cooked 1/2 cup 418 Collards, raw 1 cup 184
Swiss chard, cooked 1/2 cup 287 Swiss chard, raw 1 cup 299
Mustard greens, cooked 1/2 cup 210 Mustard greens, raw 1 cup 279
Turnip greens, cooked 1/2 cup 265 Turnip greens, raw 1 cup 138
Broccoli, cooked 1 cup 220 Broccoli, raw 1 cup 89
Brussels sprouts, cooked 1 cup 219 Endive, raw 1 cup 116
Cabbage, cooked 1/2 cup 82 Green leaf lettuce 1 cup 71
Asparagus 4 spears 48 Romaine lettuce, raw 1 cup 57
Table from "Important information to know when you are taking: Warfarin (Coumadin) and Vitamin K", Clinical Center, National Institutes of Health Drug Nutrient Interaction Task Force.

  • The prothrombin time (PT) test measures the time required for blood to clot. A blood sample is mixed with citric acid and put in a fibrometer; delayed clot formation indicates a deficiency. This test is insensitive to mild deficiency, as the values do not change until the concentration of prothrombin in the blood has declined by at least 50%.
  • Undercarboxylated prothrombin (PIVKA-II), in a study of 53 newborns, found "PT (prothrombin time) is a less sensitive marker than PIVKA II", and as indicated above, PT is unable to detect subclinical deficiencies that can be detected with PIVKA-II testing.
  • Plasma phylloquinone was found to be positively correlated with phylloquinone intake in elderly British women, but not men,
  • Urinary γ-carboxyglutamic acid 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 μg to between 377 and 417 μg for five days did not induce a significant change. Response may be age-specific.
  • Undercarboxylated osteocalcin (UcOc) levels have been inversely correlated with stores of vitamin K and bone strength in developing rat tibiae. Another study following 78 postmenopausal Korean women found a supplement regimen of vitamins K and D, and calcium, but not a regimen of vitamin D and calcium, was inversely correlated with reduced UcOc levels.
  • Rhéaume-Bleue, Kate (2012). Vitamin K2 and the Calcium Paradox. John Wiley & Sons, Canada. ISBN . 


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