Vitamin K, is an essential fat soluble vitamin. Scientists first discovered its role in blood coagulation, 1 however later they found it to have many other important functions in our body. It is needed to make sure calcium is transported to the the bones and teeth 2, 3, instead of being stored in soft tissues where it can cause major problems. This is why Vitamin K is crucial in the prevention of arterial calcification 4, 5, 6 and osteoporosis, 7, 8, 9, 10 but some studies found it can also reduce the risk of certain cancers. 7, 11, 12

There are many types of Vitamin K 

The most well known types of Vitamin K are K1, K2 MK-4 and K2 MK-7. Vitamin K3 is a less known form that is used in animal agriculture. Vitamin K1 is found mostly in plants, and in a few animal products. MK-4 is found in the fat of industrially produced animal products, while MK-7 is found in certain fermented foods. 13, 14 Interestingly, industrial meat products contain much more MK-4 then free range, or wild animal meats. This it due to the heavy use of Vitamin K3 supplementation in the meat industry world wide.  15

How much Vitamin K is found in our foods? 

Leafy green vegetables contain the highest amounts of K1, about 500 micrograms in every 100 gram serving. Legumes, fruits, and seeds also contain some K1, but to a much lesser degree. MK-4 is found in industrially produced meat, eggs and dairy products, goose liver being the richest source. MK-7 is found in aged cheeses and natto, a fermented soy product popular in Japan. During human evolution, our Vitamin K requirements were met by eating an abudance of Vitamin K1 rich vegetables and seafood. Foods containing MK-4, were simply not available. 

What is the best form of Vitamin K? 

The recommended daily intake of Vitamin K is very low, less then 100 micrograms. This is enough to activate blood clotting, but only if it is in a well absorbed form. Many doctors and scientists recommend mostly Vitamin K2, because they believe it is the form that is responsible for the benefits it provides beyond coagulation. In recent years, many studies looked at the various forms of Vitamin K, and their effect in osteoporosis, arterial calcification, and certain cancers. It is true that MK-4 is responsible for most benefits, however this does not imply that we need to provide MK-4 directly, as all other forms convert to MK-4 in our body.

What is the effective dose, of the various types? 

From Vitamin K1, the official recommendation of about 100 micrograms is only enough for blood coagulation. Much more, about 500 micrograms is needed to activate the Vitamin K dependant proteins responsible for the benefits for the bone and circulatory systems. 17, 20 Doses of a few miligrams may reduce the risk of developing certain cancers. 7, 11 In the correct dose, Vitamin K1 is just as effective, and in some cases even more effective, than the much more expensive MK-4 and MK-7, and probably leads to a more favourable balance of the K-vitamins in our tissues. 

MK-4 has only been proven to be beneficial in very large 45 mg dosages in the prevention of osteoporosis, 9 and cancer. 21 It hasn’t been proven to have any benefit in preventing cardiovascular diseases such as arterial calcification. 22  It is impossible to provide the effective dose from natural foods, as even the rich sources only contain MK-4 in microgram quantities.  

MK-7 is just as effective as K1 in activating coagulation in small doses, and 100 micrograms is proven to strengthen the bones. 8, 10, 18 Unfortunately it is not effective in reducing arterial calcification, higher doses (360 micrograms or more) can even be counterproductive, based on a new study. 19

Which type of Vitamin K should we provide? 

If someone is not taking warfarin, or other drugs that block the action of K1, then there is no good reason to provide K2 directly. If we consume some green leafy vegetables or other foods rich in K1, we can get 500-1000 micrograms from our diet alone. It is important though to cook them thoroughly and consume it with a fat source, to maximize absorption.  

As a supplement, Vitamin K1, or its combination with MK-7 is our best option to make sure we have adequate MK-4 stored in our tissues. It can be beneficial to consume up ot 5 mg of Vitamin K1 daily, as it has been proven to significantly reduce fracture rates and cancer incidence in one study, with having no side effects. Supplementing is very important for those who don’t eat enough vegetables.  

MK-4 should only be considered, if someone is taking the above mentioned drugs.

Interesting facts about Vitamin K 

Children are often born Vitamin K deficient. In order to prevent a rare, but very dangerous deficiency disease, they are given Vitamin K by either injection or orally at birth. They also receive several doses of Vitamin K weeks and months after birth, in order to prevent deficiencies. Vitamin K is extremely safe, during decades of use there haven’t been documented cases of side effects. Adults don’t have to worry about taking too much Vitamin K either, as taken in miligram dosages for years produced no adverse effects. 

[The cover photo of the note shows cabbage. 100 grams contain 830 μg of vitamin K, which is 8 times the recommended daily intake, however, this recommendation was based only on its role in blood coagulation.]