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A–Z Guide To Vitamin K Deficiency, Functions And Vitamin K Foods

A–Z Guide To Vitamin K Deficiency, Functions And Vitamin K Foods

Vitamin K is a vitamin that helps your body heal wounds, build strong bones, and maintain healthy blood vessels.

Your body doesn’t just thrive on fresh air and clean water, it requires a range of nutrients in tiny doses to keep things running smoothly. Vitamin K is one of them. Without this vitamin, you would have no scabs and no scars because your cuts and bruises wouldn’t stop bleeding.

Table of contents

Get the facts on vitamin K and find out why it’s so important for your body in this article. Discover the symptoms of vitamin K deficiency, how it’s diagnosed and what vitamin K foods you should add to your diet.

☝️DISCLAIMER☝This article is for informational purposes only. It is not intended to constitute or be a substitute for professional medical advice, diagnosis, or treatment.

What is Vitamin K?

Find out how vitamins work with this Ted ED video

Vitamin K is one of 13 vitamins that the human body needs. It is essential for blood clotting - without it, the body is not able to stop bleeding. There are two main types of vitamin K:

  • Vitamin K1, also known as phylloquinone, comes mostly from food, especially green plants.
  • Vitamin K2, also known as menaquinone, is mainly produced by gut bacteria. It also comes from fermented foods.

It is a fat-soluble vitamin, which means the body needs fat to absorb it. Fat-soluble vitamins like vitamin K are stored in the liver and adipose tissue (body fat).

In addition, some gut bacteria produce vitamin K2 and early research suggests that this is also important for heart health. Bacteria that synthesise vitamin K2 include:

Bacillus Bacteroides fragilis
Lactobacillus Serratia marcescens
Geobacillus Enterobacter agglomerans
Eubacterium lentum Enterococcus faecium

☝Find out if your microbes can make vitamin K2 and other nutrients with the Atlas Microbiome Test.

Vitamin K health benefits

Vitamin K supports critical processes that keep your body fit. It helps your body to control bleeding, and it regulates calcium absorption that can affect your bones and heart health.

Vitamin K and wound healing

Vitamin K activates the blood's clotting proteins by Paweł Czerwiński for Unsplash.
Vitamin K activates the blood's clotting proteins

The main role of vitamin K is to enable blood clotting and support wound healing. It triggers the body’s blood clotting process by converting coagulation factors (proteins that control bleeding) into their active forms. Doctors refer to these coagulation factors as vitamin K dependent clotting factors because, without vitamin K, these proteins cannot do their job.

The most common symptom of vitamin K deficiency is excessive bleeding.

Vitamin K and bone health

Vitamin D and K work together to metabolise calcium, which is essential for strong bones. Vitamin D enables the body to absorb calcium in the small intestine, and vitamin K helps your bones accumulate calcium, which keeps them strong.

Vitamin K deficiency is associated with increased risk of osteoporosis and fractures in adults over 30 years old.

Vitamin K and heart health

A growing body of research shows that vitamin K1 and K2 play a role in heart health. This nutrient regulates calcium absorption and prevents calcium from accumulating inside the blood vessels. Calcification makes them stiff and forces the heart to work harder to pump blood, which increases the risk of cardiovascular death.

Chronic kidney disease significantly increases the risk of vascular calcification and cardiovascular death.

Vitamin K in pregnancy and newborns

Pregnant women don’t normally need extra vitamin K. Low levels of vitamin K in newborn babies are common, but in some cases, it can lead to a rare but serious bleeding disorder called haemorrhagic disease of the newborn (HDN). For this reason, the UK’s National Institute for Health And Care Excellence (NICE) recommends a vitamin K injection for neonates up to 8 weeks after birth.

Oral vitamin K supplements are an alternative to injections, but require multiple doses.

Vitamin K deficiency

Vitamin K deficiency is rare in healthy adults because the body stores it in the liver and fat. Plus, it is found in many foods. However, some health conditions and medical drugs can interfere with the synthesis and absorption of vitamin K. Vitamin K deficiency symptoms in adults include:

  • mucus membrane bleeding (gums and nose)
  • bone deformities
  • bruising easily
  • tar-like stools
Atlas Microbiome Test for vitamins

Vitamin K deficiency causes

Although rare in adults, some people are at a greater risk of developing deficiency, especially if they take anticoagulants, antibiotics, eat lots of foods low in vitamin K or have a condition where their body is unable to absorb fat properly, like coeliac disease.

Warfarin is a vitamin K antagonist: it blocks the action of vitamin K. This medication functions as a blood thinner to prevent blod clots.


Blood tests are used to diagnose vitamin K deficiency. The main lab test is called prothrombin time. It measures the time it takes, in seconds, for blood plasma (the fluid part of blood) to clot.

  • People with a deficiency have fewer vitamin K dependent factors II, VII, IX and X, which increases prothrombin time.

Another measure, known as international normalised ratio or INR, is used for people who take vitamin K antagonists like warfarin. INR results are monitored regularly to ensure they are receiving the correct dosage of medication.

  • People who take a vitamin K antagonist like warfarin, which is designed to lower the action of vitamin K, may need regular INR testing.


Short-term treatment for deficiency often involves oral vitamin K supplements. Individuals who have long-term conditions may need to take them for a prolonged time or for life. In some cases, such as bleeding whilst taking vitamin K antagonists, patients may require a vitamin K IV (intravenous therapy).

How to prevent vitamin K deficiency

Vitamin K is abundant in green vegetables by Dose Juice for Unsplash.
Vitamin K is abundant in green vegetables

According to the NHS, adults require 1 microgram (mcg) of vitamin K per day per kilogram of body weight. So if you weigh 70 kilograms, you’ll need 70 mcg of vitamin K every day.

Vitamin K foods

A microgram is tiny - one thousand times smaller than a milligram. So by eating a healthy, balanced diet, all humans should acquire the vitamin K they need. In foods like green leafy vegetables and spinach, vitamin K levels are high enough to meet your body’s needs.

beef liver broccoli avocado
cheese brussels sprouts kiwi
chicken cabbage prunes
goose liver green beans and peas natto
turkey spinach soybean oil


Vitamin K is an essential fat-soluble vitamin that the body needs for adequate blood clotting, strong bones and heart health. Vitamin K deficiencies are rare in healthy adults because you can get all you need by eating a varied and balanced diet. However, there are certain factors which can interfere with your levels such as chronic illness and certain medications.

Leanne Edermaniger
Leanne Edermaniger Science writer who enjoys laughing which is proven to help you live longer.

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