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Vitamin K deficiency: Bleeding and blood clots

Vitamin K deficiency: Bleeding and blood clots

A fat-soluble nutrient, vitamin K is best known for its role in blood clotting (coagulation). A Danish biochemist called Carl Peter Henrik Dam discovered it in the late 1920s while working on studies on cholesterol metabolism at the University of Copenhagen. In 1943 Dam was awarded the Nobel Prize in Medicine or Physiology for his discovery, sharing the prestigious award with an American biochemist, Edward Doisy, who described vitamin K’s chemical structure (i).
There are two forms of vitamin K: vitamin K1 and vitamin K2 (there is also a third, K3, though this is a synthetic vitamin that’s considered unsafe for human consumption). Vitamin K1 (also called phylloquinone) is the main type involved in blood coagulation.
A process that helps prevent excessive bleeding in and outside of the body, coagulation is essential for health. If your blood doesn’t clot properly you may bruise easily and have lots of nosebleeds or heavy periods (menorrhagia). And if you injure yourself or have surgery, it may take longer than normal for the bleeding to stop.


How your blood clots

If you scratch or cut yourself or damage a blood vessel some other way (externally or internally), your body needs to stop and repair the injury so that you don’t bleed excessively. The exact process of coagulation still isn’t fully understood, but experts believe the following happens (ii):

  1. First, the muscles in the wall of the damaged blood vessel shrink so that less blood can leak out.

  2. Platelets – fragments of blood cells – and proteins called clotting factors are activated, working together to form a clot (sometimes called a platelet plug) over the damaged area. A substance called von Willebrand factor is released by the lining of the blood vessel cells – this attaches to the platelets and helps them stick together. All of this happens within seconds of the damage and helps slow down and stop the bleeding.

  3. Within a few minutes clotting factors in the blood work together to turn a protein called fibrinogen into fibrin, a substance that forms a stronger clot over the top of the platelet plug. This second, stronger clot holds the first clot in place and stops any more blood from flowing out.

  4. The fibrin also acts as a structure for new tissues to grow on – this naturally dissolves and is removed from the body after the injury has healed.


How does vitamin K affect blood clotting?

As for vitamin K’s role in this process, scientists discovered some time ago that it helps the liver make some of the clotting factors involved in coagulation (iii), including one called prothrombin (also known as factor II).

Vitamin K deficiency and bleeding in babies

Vitamin K deficiency is very rare in adults. A condition called vitamin K deficiency bleeding, however, is more common in babies (though again it’s still quite rare). That’s because babies have very little vitamin K in their bodies when they’re born, and some – a small number – may bleed as a result. Often, a baby with vitamin K deficiency bleeding will bleed internally, which can be difficult to spot.
All babies have a risk of developing vitamin K deficiency bleeding until they start eating regular foods that help build up their vitamin K levels.     .

Treatments for vitamin K deficiency bleeding in babies

However all newborn babies in the UK are recommended to have a vitamin K supplement straight after they are born to reduce the risk of bleeding.
Here in the UK newborns can have a vitamin K injection immediately after they’re born or within a few hours of the birth. They can also have vitamin K by mouth – though if you choose this method for your baby they will need two doses in their first week if they are feeding with formula milk (which contains some added vitamin K) or two doses in their first week and another when they’re a month old if they are being breastfed (breast milk only contains a small amount of vitamin K).

How common is vitamin K deficiency bleeding in babies

According to the NHS, about one in 10,000 full-term babies experience vitamin K deficiency bleeding if they don’t get extra vitamin K when they are born: this means of the 800,000 recorded births in the UK every year, 10 to 20 babies could be brain damaged as a result of a bleed in the brain and four to six babies could die (iv).
Some babies also have a higher risk than others of developing vitamin K deficiency bleeding. For instance, within the first 24 hours after birth, babies born of mothers taking certain medicines – including anti-convulsant drugs – have a higher risk of bleeding. Others who have a greater risk of bleeding after 24 hours following birth include:

  • Premature babies

  • Babies who had a complicated delivery (a forceps delivery, for instance)

  • Babies with liver disease (symptoms include jaundice that lasts after they are two weeks old, dark urine and pale stools)

  • Babies who have difficulties with feeding or who find it hard to absorb feed

  • Babies who are ill for other reasons

  • Babies who previously experienced bleeding

If you’re pregnant your midwife will give you all the facts you need to know about the vitamin K injection so you can make an informed decision about whether or not your baby should have it when they’re born.

Vitamin K deficiency in adults

If you have a healthy, nutritious diet you should be getting plenty of vitamin K as it’s found in a range of foods. Your gut bacteria also make vitamin K – in fact, scientists believe around 10 per cent of the vitamin K absorbed by your body is thought to come from that made in your large intestine (v).
Some people, however, may be more likely to be deficient in vitamin K because they have a health problem such as: 

People taking long-term antibiotic medicines are also at risk of being deficient in vitamin K. Other medicines that can lower your vitamin K levels include the weight-loss drug orlistat and drugs called bile acid sequestrants, which are sometimes prescribed to lower cholesterol levels. And, of course, if your diet is extremely low in foods that contain vitamin K, you may also be at risk of developing a deficiency.

Vitamin K deficiency symptoms in adults

Bleeding for a long time after cutting or injuring yourself is the most obvious symptom of vitamin K deficiency in adults. Other symptoms include frequent nosebleeds, skin that bruises easily, heavy periods and very dark stools. Some people also notice small blood clots under their nails if they are deficient in vitamin K.
If you think you may have a problem with vitamin K deficiency, see your GP. The main treatment is vitamin K supplements, though you may also need a vitamin K injection in some circumstances.

What are bleeding disorders?

Bleeding disorders are also rare and include haemophilia and von Willebrand disorder:

  • Haemophilia is caused by low levels or a complete lack of one of the clotting factors needed for coagulation, causing bleeding that takes longer than normal to stop (bleeding can also happen internally without injury – this is called spontaneous bleeding)

  • von Willebrand disorder is caused by low levels of von Willebrand factor, which is also important for blood clotting. This also causes bleeding that takes a long time to stop

These and other rare blood disorders are almost always inherited, which means they are caused by a problem with your genes and not a deficiency of vitamin K.
According to the Haemophilia Society, von Willebrand disorder is the most common bleeding disorder, with 7,071 women and 4,081 men currently diagnosed in the UK (though many more may be undiagnosed). Haemophilia type A, on the other hand, is probably the best-     known bleeding disorder, affecting almost exclusively men (8,740 people are currently living with it in the UK). There are several other types, and overall around one in every 2,000 men, women and children in the UK is thought to have a diagnosed bleeding disorder (vi).

How to keep your vitamin K levels up

Even if you’re not vitamin K deficient, making sure you’re getting plenty of vitamin K in your diet can help keep your coagulation working optimally. Vitamin K1 is mostly found in plant foods, and because it’s a fat-soluble vitamin it’s absorbed more effectively when you combine vitamin K1 foods with butter or oils.
Here are a few of the main foods that contain vitamin K1:

  • Green leafy vegetables such as spinach, lettuce, watercress, Swiss chard and kale

  • Cabbage, broccoli, Brussel sprouts and cauliflower

  • Avocados

  • Kiwi fruit

  • Grapes

  • Onions

  • Asparagus

  • Soya beans

  • Plant oils (olive, rapeseed, soya)

  • Kidney beans

  • Plums

There is an extensive list of foods and the amounts of vitamin K1 they contain on the US-based National Institutes of Health website here
Recommendations for how much vitamin K we need in our diets tend to focus on a combination of the two main types, rather than individual figures for vitamin K1 and vitamin K2. According to the NHS, adults need around one microgram of vitamin K a day for each kilogram of their body weight (vii). The European Food Safety Authority, meanwhile, has published daily adequate intake requirements for vitamin K for different age groups (viii):

  • 70 micrograms for adults (including pregnant and breastfeeding women)

  • 65 micrograms for teenagers aged 15 - 17 years

  • 45 micrograms for children aged 11- 14

  • 30 micrograms for children aged 7 - 10

  • 20 micrograms for children aged 4 - 6

  • 12 micrograms for children aged 1 - 3

  • 10 micrograms for babies aged 7 - 11 months

Making sure you’re getting plenty of vitamin K in your diet is an ideal goal. But if you don’t always eat as healthily as you should, you may want to consider taking a vitamin K supplement (these are widely available, though vitamin K1 is often combined with other nutrients in supplements).

Vitamin K and warfarin

Warfarin is an anticoagulant medicine used to prevent the risk of blood clots in people with certain medical conditions. It works by blocking the production of an enzyme that helps activate vitamin K in the body. If you take warfarin you’ll need regular blood tests to check your blood coagulation and your vitamin K levels.
Your doctor or specialist will usually talk to you about your vitamin K intake if you’re on warfarin because it’s important to eat around the same recommended amount every day. That’s because suddenly eating too many vitamin K-rich foods could increase your risk of having a blood clot or even increase your risk of bleeding if you eat too few. 
People taking warfarin are therefore usually advised not to take vitamin K supplements without the advice of their specialist. Always speak to your doctor if you’re not sure how much vitamin K you should be getting through food while taking warfarin.

Need more information?

For more details about vitamin K1 as well as vitamin K2, read our article Bone health: the importance of vitamin K. There’s also lots of information about blood and circulatory disorders in the circulatory health section of our pharmacy health library


  1. Available online:

  2. Available online:

  3. , Vitamin K and its role in blood coagulation. American Journal of Surgery volume 57, issue 1 July 1942, 104-111. Available online:

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  5. , Wardlaw’s perspectives in nutrition. New York, NY: McGraw-Hill. Available online:

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Disclaimer: The information presented by Nature's Best is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications.

Our Author - Christine Morgan


Christine Morgan has been a freelance health and wellbeing journalist for almost 20 years, having written for numerous publications including the Daily Mirror, S Magazine, Top Sante, Healthy, Woman & Home, Zest, Allergy, Healthy Times and Pregnancy & Birth; she has also edited several titles such as Women’ Health, Shine’s Real Health & Beauty and All About Health.

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