What is vitamin K?
Understand why we need this vital vitamin and which foods are useful sources, plus what to consider if you’re on prescribed medication.
Vitamin K plays an important role in the body, supporting blood clotting, wound healing and the formation and maintenance of healthy bones. How well we absorb vitamin K depends on its form and dietary source. For example, absorption from green leafy vegetables may be as low as 4-17%. Read on to find out more.
Check out our Vitamins and Minerals Information Hub to learn more about key nutrients – from whether you’re getting enough vitamin D to the top 10 healthiest sources of vitamin C, plus vital minerals you need in your diet.
What is vitamin K?
Vitamin K is the name given to a group of fat-soluble vitamins that can be stored by the body. There are two main forms: vitamin K1 and K2.
- Vitamin K1 (phylloquinone) is mostly found in plants and their oils, and is the main source of vitamin K that we obtain from our diet.
- Vitamin K2 (menaquinone) is found in fermented foods and some meat, including liver, as well as cheese and eggs. It may also be produced by the bacteria that live in your gut.
Why do we need vitamin K?
Vitamin K activates proteins that play an important role in blood clotting, so it helps wounds heal. It regulates our use of calcium, so is relevant for strong, healthy bones and is important for a healthy heart and circulation.
The health benefits of vitamin K include:
- Supports blood clotting and wound healing
- Improves bone health and may lower the risk of osteoporosis
- Improves dental health
- May help prevent heart disease
- May help prevent cancer
Recent research suggests there may be further roles for vitamin K to play in maintaining the health of our brain, joints, nerves and eyes.
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How much vitamin K do we need?
In the UK, the recommended daily intake of vitamin K for adults is 1 microgram a day for each kilogram of body weight. This means an adult who weighs 65kg would need 65 micrograms (mcg) of vitamin K per day.
The good news is, most of us get all we need either through eating a varied, balanced diet, or from the production of vitamin K2 in our gut – in fact, a healthy microbiome produces enough vitamin K to cover your daily needs.
Can we have too much vitamin K?
It is very difficult to obtain too much vitamin K from dietary sources. As a vitamin, it has very low potential for toxicity, because unlike other fat-soluble vitamins, it can be broken down relatively quickly and eliminated through urine and faeces. For this reason, there is no established upper safe level for vitamin K.
Where care is needed, however, is if you are prescribed anti-coagulant medication – in this circumstance, you should avoid large fluctuations in your vitamin K intake. This is because the clotting factor, prothrombin, is a vitamin K-activated protein. Anticoagulants antagonise vitamin K, and therefore control the degree of clotting in the body. Any sudden increase or drop in levels may affect how the medication works.
What are the signs of a vitamin K deficiency?
The majority of us obtain enough vitamin K either from our diets or gut microbiota. Without vitamin K, our ability to form blood clots would be impaired, and we’d experience problems with bleeding, including possible haemorrhage; low levels of vitamin K may also weaken bones and promote calcification of the arteries, which may lead to heart disease.
People most at risk of a vitamin K deficiency may include:
- Those following a severely restricted diet, including one that is very low in fat
- Those with a genetic disposition that makes them less able to utilise vitamin K
- Those with liver disease
- Those with a severe gut imbalance or on long-term antibiotic therapy
- Those on long-term anticoagulants
Newborn babies have very low levels of vitamin K, because it's a micronutrient that doesn’t cross the placenta well. In addition to this, breast milk contains only small amounts. Therefore, all newborn babies need vitamin K from another source.
Which foods are sources of vitamin K?
Dietary vitamin K is largely obtained from green leafy vegetables and vegetable oils, with lesser amounts found in dairy, meat and eggs.
Vitamin K1 is found in:
- Brussels sprouts
- Soya beans
- Swiss chard
- Vegetable oils, including soya and rapeseed
Vitamin K2 is found in:
- Beef mince
- Chicken liver
Fermented foods are also valuable sources of vitamin K2, which is the form stored in the liver. Examples include:
Get inspired with these delicious recipes that contribute vitamin K:
Raspberry kefir overnight oats
Poached eggs with broccoli, tomatoes & wholemeal flatbread
Lamb, turnip & celariac hotpot
Broccoli & stilton soup
Chicken livers on toast
Speak to your GP or healthcare provider if you're concerned about your vitamin K levels or how it may interact with prescribed medication.
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This article was reviewed on 16 November 2023 by Kerry Torrens.
Emer is a specialist dietitian who combines her love of food and science to help increase people’s awareness of a healthy lifestyle. An expert in IBS, weight loss and women’s health, she brings energy and passion to her profession and enjoys bringing the science of nutrition to life. In ebook IBS? Recipes For Success, Emer shares quick and easy recipes for people suffering from IBS, combining her passion for cooking with her expert knowledge. She has worked in top London teaching hospitals and balances her time between her media work, private clients and NHS commitments.
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