Vitamin K

Little-known but essential, vitamin K helps blood to clot. Most vitamin K is produced by bacteria in the gut, although there are also a few vitamin K-containing foods.

How much vitamin K do we need?

  Age (years) AI*
Vitamin K (µg/day)
Infants 7-12 months 2.5
Children 1-3 25
  4-8 35
  9-13 45
  14-18 55
Men 19-70+ 70
Women 19-70+ 60
Pregnant and breastfeeding women 14-50 60
*Adequate Intake 
 

Who needs more and why?

It is highly recommended that all babies are given a Vitamin K injection at birth. Babies have low levels of this vitamin as they have less bacteria in their gut where Vitamin K would be made and babies do not receive enough Vitamin K from their Mothers. Without the Vitamin K injection babies are at great risk of serious bleeding and developing a rare bleeding disorder.  

Which foods contain vitamin K?

Vitamin K is found in green, leafy vegetables (such as spinach, broccoli, brussels sprouts, cabbage, lettuce), soybean and canola oils. Some milk products are fortified with vitamin K. However most vitamin K is produced by bacteria in the gut.

Medications and vitamin K

Warfarin is a blood thinning medication given to people to reduce the risk of blood clots forming in their body, which is the direct opposite action of Vitamin K which clots blood. People taking warfarin need to keep the amount of Vitamin K from foods and supplements in their diet constant. If the levels of Vitamin K consumed vary significantly then medication levels need to be changed to match this. This needs to be discussed and monitored by a doctor with support from a registered dietitian or nutritionist. Such changes may occur:

  • during summer if more salad greens, are being eaten
  • when certain high vitamin K vegetables are in season, such as Brussels sprouts
  • if cooking oil is changed  to canola or soya which are both high in Vitamin K

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Page reviewed April 2013