Vitamin K

Vitamin K is a fat-soluble vitamin named after the initial from the German word, koagulation. Three types of compound have vitamin K activity: phylloquinone (K1), menaquinones (K2) and menadione (K3).

Bacteria in the gut produce some vitamin K2 which can be absorbed and used.

High doses of vitamin K are used to counteract over dose of the blood-thinning drug, warfarin. Seek medical advice before taking supplements containing vitamin K if you are taking warfarin treatment (e.g. for a previous blood clotting disorder). It is unlikely that dietary sources would provide enough vitamin K to interact with warfarin, e.g. you would have to eat the equivalent of 250g broccoli or cauliflower daily to have a significant effect.

Why you need it

Vitamin K is essential for normal blood clotting. It acts as an essential cofactor for the production of clotting proteins II, VII, IX, X, protein C and protein S in the liver.

A single dose of vitamin K (by injection or orally) is offered to all newborn infants to prevent a condition known as haemorrhagic disease of the newborn. This arises during the first few days of life and causes haemorrhage into the brain due to vitamin K deficiency. Some research initially suggested an increased risk of childhood leukaemia associated with giving vitamin K by injection (rather than orally) at birth, but this has now been refuted.

Vitamin K is also needed for the synthesis of osteocalcin - a calcium-binding protein found in bone matrix. Vitamin K is now recognized as being as important for bone health as the mineral, calcium.

Research

Lack of vitamin K has been linked to thinning bones and osteoporosis. In one study, when vitamin K supplements were given to postmenopausal women, bone loss was reduced and their bones became stronger. Research suggests vitamin K supplement can reduce loss of bone calcium in post-menopausal women by up to 50 per cent.

How much you need

No EC RDA for vitamin K is currently set. Requirements are thought to be around 1mcg per kilogram of body weight per day.

Symptoms that may be due to lack of vitamin K include:

  • prolonged bleeding time
  • easy bruising
  • recurrent nose bleeds
  • heavy periods
  • diarrhoea
  • osteoporosis

Foods containing vitamin K include:

  • cauliflower (richest source)
  • broccoli
  • dark green leafy vegetables
  • kelp
  • yoghurt
  • egg yolk
  • alfalfa
  • safflower, rapeseed, soya and olive oils
  • fish liver oils
  • liver
  • tomatoes
  • meat
  • potatoes
  • pulses

Bacteria in the gut produce some vitamin K which can be absorbed and used. Seek medical advice before taking supplements containing vitamin K if you are taking warfarin treatment (e.g. for a previous blood-clotting disorder).


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