Vitamin K

Vitamin K is hitting the news pages more lately as it has been discovered that it is very effective at preventing heart attacks1 and osteoporosis (brittle bone disease). It was originally known, and named, for its ability to help blood clotting. What has come to light over the last ten years, is that there are two major types of vitamin K: K1 helps with blood clotting, and K2 helps to prevent heart attacks, osteoporosis and also effective blood clotting,

Types of vitamin K

Vitamin K1

Originally the form of vitamin K originally found was phylloquinine, what is now denoted as vitamin K1. It is available from green leafy vegetables, and some other plant sources, where it is used in the process called photosynthesis, that makes sugar from carbon dioxide, water and sunlight. This sugar can then be used for energy. Vitamin K1 helps the liver create proteins that are used in the blood clotting cascade. Most of these proteins help blood clot, while a few help prevent it clotting too much. K1 was the first type of vitamin K to be discovered, and was found in the 1920's by Danish researchers. These researchers gave chickens a no cholesterol / no vitamin K diet, that caused them to bleed incessantly. Restoring cholesterol to their diet did not prevent the bleeding, only by restoring vitamin K as well was the bleeding able to be halted.

Vitamin K2

Another type has since been found called menaquinone, denoted as vitamin K2. It is found in organ meats, pastuerised dairy products, eggs, sauerkraut and natto. It can also be made in small amounts by our intestinal bacteria from vitamin K1. Vitamin K2 is the form of vitamin K that seems to have most beneficial effects on the body. It has a number of different forms denoted by MK-n where n is a number between 4 and 13. The "n" represents the number of repeating 4 carbon units on the side chain. For instance, you can see at the right that MK-7 has 4 more downward pointing spikes on its sidechain than MK-4. The form of vitamin K2 found most often in supplements is MK-7. However, this form is probably not as good as the MK-4 form which seems to be the form most commonly produced by animals. MK-4 produces all of the known beneficial effects on defurring the arteries, strengthening the bones, and helping blood clot safely. No other types of vitamin K2 have yet been found that produce as many of the beneficial effects that MK-4 has.

Vitamin K3

A third type of vitamin K is produced artificially, and is called menadione. It looks like the vitamin K molecules pictured to the right, except it has not got a side chain. It is toxic in excess, unlike the other types of vitamin K. K3 is water soluble, whereas K1 and K2 are fat soluble and require adequate secretion of bile from the gall bladder, and pancreatic juice from the pancreas in order to be properly absorbed. People without adequate bile secretion used to be put on K3 supplements if they were deficient. However due to the liver toxicity and damage to red blood cells that vitamin K3 caused, K3 supplements are no longer used.

Functions in the body

Vitamin K affects a number of proteins in the body. The best known are those produced in the liver that affect blood clotting. The next best known are the vitamin K activated proteins associated with arterial calcification and bone density. Less well known are changes to proteins and other molecules that affect the likelihood of developing many cancers and heart disease.

Vitamin K is primarily an activator of proteins, although it can also lead to the creation of new ones. We know that vitamins A and D are effective at producing the proteins that vitamin K activates. Since all three of these vitamins: A, D and K are fat soluble, it is a good idea to eat fatty foods that contain plenty of each. One particular food that is very good in this regard is organ meats such as liver. The meal shown to the left of liver, butter and sage would provide a good healthy combination of all three. The side dressing of cress, would provide some vitamin K1 also.

Blood clotting.

The effects on blood coagulation were the first to be discovered. Vitamin K1 helps the liver create the proteins that help blood to clot. Because not much vitamin K is stored in the body it is important that good use is made of dietary supplies. This is achieved  by the vitamin K cycle, which reuses K, thus reducing the need for it in the diet. Vitamin K2 especially the form MK-4 is also associated with proper blood clotting.

A sign that we don't consume enough vitamin K1 or K2 in the modern world, is that in many countries newborn babies are given a shot of vitamin K shortly after birth, in order to prevent them bleeding too easily. The MK-4 form of vitamin K2, is used in Japan in to prevent blood loss in newborn babies, while in other countries vitamin K1 is more often used. The MK-4 form of vitamin K is found in colostrum (breast milk the baby receives during its initial feed), and hind milk (the last milk the available towards the end of any breast feeding session). It seems likely that if enough vitamin K2 is being consumed by the mother, and breast feeding is not terminated too soon, that most babies would receive enough vitamin K.

Improving bone density.

Vitamin K2 is associated with proper handling of calcium in the body. It seems to prevent calcium being depositied in the arteries, and instead ensures that the calcium is used to build stronger bones. Evidence that bone fractures are reduced after intake of vitamin K2 has been produced  in Japan2. The type of vitamin K2 that was shown to be effective in Japan was MK-4. So, while most people have heard that consuming more calcium can help build stronger bones, this strategy is unlikely to work unless you are also consuming good amounts of vitamin K2.

Keeping arteries defurred.

There is good evidence that vitamin K2 is able to reduce the amount of calcium that is furring up arteries3, while vitamin K1 does not seem to be able to prevent calcification of the arteries in humans4. The rats used in the study that showed this were able to convert vitamin K1 into vitamin K2 easily. However, it seems that humans have more difficulty. This is why consuming enough vitamin K2 in the diet is important for us. It is interesting that the very foods so often vilified by the medical community are the ones that contain plenty of vitamin K2. For example people eating plenty of cheese, milk, butter and meat, which are high in vitamin K2, would also be consuming plenty of cholesterol and saturated fat. However, as I've investigated previously here, there is not much good evidence that consuming plenty of either will do you any harm.

Things that prevent vitamin K working properly

Warfarin (coumadin)

Otherwise known as rat poison, Warfarin is a commonly used drug that is used to prevent unwanted blood clotting. It interferes with the vitamin K cycle and prevents vitamin K1 being converted in vitamin K2. These actions help prevent clotting, but in the long term the lack of vitamin K2 has potentially serious implications for bone mineral density and arterial calcification as vitamin K's ability to help build bone and clean up the arteries are reduced. Current advice is to consume moderate amounts of vitamin K if you are on warfarin. In most cases it would be best to consume this from foods rather than as supplements.

Broad spectrum antibiotics

Amoxycillin, Metronidazole, Levofloxacin etc. These prevent the bacteria in our gut converting vitamin K1 into the more useful vitamin K2. Lack of vitamin K2 could lead to easy bleeding as well as reduced bone density.

Anti-epilepsy drugs

Carbamazepine, Gabapentin, Phenytoin, Valproate etc. These interfere with the liver's production of vitamin K dependent proteins.

Some drugs for weight or cholesterol control

Cholestyramine, Orlistat etc. These prevent absorption of vitamin K by interfering with bile secretion.

Coeliac disease and pancreatic insufficiency

Both these conditions restrict the amount of vitamin K that can be absorbed from the gut.

Alcoholism, Cystic Fibrosis, and IBDs

Alcoholism, Cystic Fibrosis and Inflammatory bowel disorders also interfere with vitamin K metabolism.

Sources in the diet

  • Green leafy vegetables and blackstrap molasses contain vitamin K as phylloquinone, K1. Bear in mind that as a fat soluble vitamin, absorption of the K1 is likely to be between 3-10 times more efficient, if a source of fat is included with the K1. So spinach with butter and stir fried kale are all better than the steamed varieties for vitamin K absorption.
  • Organ meats, pastuerised dairy such as milk and cheese, eggs and shellfish provide vitamin K2 in the form of MK4.
  • Sauerkraut, natto and miso contain vitamin K2 in the form of MK7.

The proportion of dietary vitamin K that is absorbed in the intestines can vary from 5% upwards6. In the form of vitamin K1 in green leafy vegetables as little as 5% may be absorbed, whereas in the form of vitamin K2 more is generally absorbed. 

Testing for deficiency

The normal range of plasma vitamin K in adults is 0.2-3.2 ng/ml, although a lab in South Carolina uses 0.13-1.19ng/ml5. Levels below 0.5ng/ml could be taken to indicate deficiency in vitamin K, but it is not considered a reliable test, as levels can vary quickly, dependent on recent intake. As such this test is not used to test for deficiency. If blood is failing to clot properly, which is more likely with plasma vitamin K levels under 0.5ng/ml then a prothrombin time is measured, and if it is too low vitamin K deficiency may be suspected.


The level of daily vitamin K intake has been suggested at around 100microgram (ug) by most health authorities. Vitamin K1 levels plateau in the blood with an intake provided by about 1/4 cup of spinach and so from a K1 perspective most people probably don't need more than this. When it comes to vitamin K2 it looks likely that a lot of people are not currently consuming enough to reduce their risk of heart disease and osteoporosis. Supplements are available, but it is probably best to eat plenty of those foods that contain vitamin K2.

Vitamin K supplements can be found in quite a few types of multi-vitamin pill, often in the K1 form. Currently vitamin K1 is the type most commonly used in the UK and USA for therapeutic use. It is used for newborn babies, as mentioned above, and also before hospital operations where excessive bleeding is commonly encountered. However, it is worth being aware that vitamin K2, especially the MK-7 form is quite popular in many supplements, whereas the MK-4 form is most likely of more benefit for health. The cost of vitamin K2 appears to be significantly more than that of vitamin K1 for the same quantity. The K1 form of vitamin K is not so beneficial for most people, unless they have problems with blood clotting. 

Vitamin K1 and K2 have not been found to be toxic in large amounts, and so supplementation should be safe for most people. However vitamin K3 is not so safe, and is best avoided.

DrDobbin says:

Vitamin K, and especially the K2 form are very important for heart and bone health. They are generally overlooked, but are likely to be given increasing coverage over the next two decades. I'd encourage you to look at the best sources for vitamin K2 (organ meats, pastuerised dairy such as milk and cheese, eggs and shellfish) and include them in your regular diet. If you are vegan I'd recommend trying some of the Japanese sources like natto and miso soup.


I should mention that I have referenced Stephen Guyenet's blog at: in compiling this article.

1) supports MK-7, 8 and 9 reducing CHD incidence.

2) supports role of MK-4 in reduced fracture rate in humans from 7 separate trials.

3) evidence that arterial calcification can be reversed bby menaquinone.

4) suggests that MK-4, but not K1 is effective at reversing artierial calcification.

5) labtest for vitamin K.

6) Low absorption % for vitamin K1 from kale.