A dietitian explains why we need this vital vitamin, how much we need, and the best dietary sources, plus how vitamin K can interact with medications.
Vitamin K plays an important role in the body, helping with blood clotting, wound healing and the formation of bones. You should be able to get all you need from a varied, healthy diet.
Always speak to your GP or healthcare provider before taking a new supplement or if you are concerned about nutritional deficiencies.
What is vitamin K?
Vitamin K is a fat soluble vitamin that can be stored by the body. There are two forms of vitamin K: K1 and K2. Vitamin K1 is mostly found in plants and is the main dietary source of vitamin K. Vitamin K2 is found in fermented foods and in some meats and cheeses. It is also made by our body from the vitamin K1 in the food we eat.
Why do we need vitamin K?
Vitamin K plays an important role in the body – in particular, it is involved in blood clotting (helping with wound healing) and bone formation. The clotting factor, prothrombin, is a vitamin K-dependent protein directly involved in blood clotting. Anticoagulants (blood thinners), such as Warfarin (Coumadin®), antagonise vitamin K activity and therefore consistent vitamin K intakes are advised for those on this medication, as a sudden increase or drop in levels of vitamin K can affect how this medication works.
Speak to your GP or healthcare provider if you're concerned about your vitamin K levels or how it might interact with medications.
How much vitamin K do we need?
The NHS states that adults need approximately 1 microgram a day of vitamin K for each kilogram of their body weight. You don't need to eat it every day, as any unused vitamin K is stored by the body in the liver for future use.
You should be able to get all the vitamin K you need by eating a balanced diet and it is very difficult to take too much vitamin K from dietary sources. People taking anticoagulation medicine should avoid vitamin K supplements.
Which foods are good sources of vitamin K?
Dietary vitamin K is largely obtained from green leafy vegetables and vegetable oils, with lesser amounts present in dairy products, meat and eggs, broccoli, soybeans, dark green leafy vegetables such as kale, turnip/beet greens and spinach.
More on vitamins and minerals
This article was published on 6 August 2019.
Emer Delaney BSc (Hons), RD has an honours degree in Human Nutrition and Dietetics from the University of Ulster. She has worked as a dietitian in some of London's top teaching hospitals and is currently based in Chelsea.
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