Vitamin K

Vitamin K is usually the nutrient that most people don’t know anything about or haven’t even heard of before. It is a fat soluble vitamin and it’s most important role is involved in the formation of a blood clot. Vitamin K is made up of a family of compounds also known as quinones and is used by the liver to make blood clotting factors and is also really important in activating these factors when blood clotting is needed. It may also have an important role in bone metabolism. Vitamin K comes from both food sources and bacteria living in the large intestine (colon).

Due to it’s role in blood clot formation, vitamin K deficiency puts people at risk of haemorrhage or excessive bleeding because of problems in the blood clotting process.

It is quite rare for a person to become vitamin K deficient, however it can occur with prolonged use of antibiotics which may affect the bacteria in the colon that make it. Vitamin K deficiency can also occur in newborn babies who are generally born with low vitamin K stores. Because of the risk of excessive bleeding, babies are routinely given vitamin K injections after delivery to prevent major haemorrhage. Other risk factors for vitamin K deficiency is excessive intake of either vitamin A or vitamin E which can hinder the absorption of vitamin K from the intestine and disrupt the amount of clotting factors dependent on vitamin K to function correctly.

Food Sources of Vitamin K

About 10% of all vitamin K absorbed from the intestine comes from the bacteria that live in the colon. The other 90% comes from food sources such as kale, turnip greens, parsley, lettuce, cabbage, spinach, rocket, broccoli, peas, asparagus, Brussels sprouts, soybean oil and canola oil.

How Much Vitamin K Do We Need?

The Adequate Intake (AI) level for vitamin K is 70ug/day for men and 60ug/day for women and this doesn’t change for either pregnancy or breastfeeding (NHMRC).

Meal and Snack Ideas

  • A salad made up of green leafy vegetables such as spinach, rocket or other salad greens and dressed with a vegetable oil is a fantastic way to ensure sufficient vitamin K intake.
  • Add spinach or kale to quiches, pastas or pastries.
  • Toss blanched green beans, asparagus and snow peas in canola oil and minced garlic and lightly fry for a couple of minutes or until cooked to your liking. Serve with a portion of chicken, meat or fish.

Too Much of a Good Thing?

There is no Upper Limit (UL) level set for vitamin K as it is more readily excreted than the other fat soluble vitamins (vitamin A, vitamin D and vitamin E). The synthetic form (from supplements) of vitamin K, menadione, can cause haemolytic anemia, excess bilirubin in the blood and death in newborns babies.

References:
  • Nutrient Reference Values for Australia and New Zealand, National Health and Medical Research Council
  • Wardlaw’s Perspectives in Nutrition 8th Edition, Byrd-Bredbenner, 2009.

See my other fact sheets:

Vitamin A

Vitamin D

Vitamin E

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About Kate Freeman

I am a Registered Nutritionist (RNutr) and I'm passionate about providing honest, simple nutrition advice and doing it in such a way that inspires and motivates you to make positive lifestyle changes to achieve your health and nutritional goals. I am married with 2 children and live in New South Wales, Australia.

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