Vitamin K

The fat-soluble vitamin K is essential for the functioning of several proteins involved in blood clotting (1). There are two naturally occurring forms of vitamin K: vitamin K1 (phylloquinone) is synthesized by plants; Vitamin K2 forms (menaquinones) can be found mainly in dairy products and are also produced to a minor extent by bacteria in the digestive tract of animals (2).

Next to its classical role in blood clotting, several potential health benefits are described for vitamin K. There is increasing scientific evidence that different forms of vitamin K have varying and accentuated impacts on disease risk reduction.

Health functions

The only known unequivocal biological role of vitamin K is as a cofactor for an enzyme that enables specific proteins to bind calcium (3, 4).

Disease risk reduction

Large epidemiological studies have demonstrated a relationship between vitamin K and age-related bone loss (osteoporosis).

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Things to know about Vitamin K

  • Intake recommendations

    Because of the lack of specific information about the vitamin K requirement, the European Scientific Committee for Food has set no population reference intakes (PRI) for vitamin K but considers a daily intake of 1 microgram (mcg) per kilogram (kg) body weight to be adequate and provided by a normal diet (25).

  • Supply situation

    Surveys in some European countries have provided estimated mean dietary intakes for vitamin K: in the United Kingdom, an average intake of 68 micrograms (mcg) per person per day was established (28), while in The Netherlands mean daily per capita intake was estimated to be up to 250 micrograms (mcg) (29).

  • Deficiency

    Overt vitamin K deficiency results in impaired blood clotting, usually demonstrated by laboratory tests that measure clotting time.

  • Sources

    Vitamin K1 (phylloquinone), the major dietary form of vitamin K, mainly can be found in green leafy vegetables, such as kale, parsley and broccoli and some vegetable oils (soybean, cottonseed, canola and olive).

  • Safety

    In healthy subjects, there is no known safety risk associated with high doses of vitamin K1 (phylloquinone) or vitamin K2 (menaquinone) forms of vitamin K (27).

  • References

    Consult the full list of scientific references.