What is vitamin K?

There are actually two types of vitamin K, and their roles are quite different.

Vitamin K1 is used by the liver for the synthesis of a certain protein – prothrombin – that enables blood coagulation. So a lack of K1 would result in uncontrolled bleeding.

Vitamin K2 activates proteins that bind calcium in bones and other tissues. A deficiency may weaken bones, leading to osteoporosis and may promote calcification of arteries. Research shows K2 can help prevent cardiovascular disease (1), improve bone density – thus guarding against osteoporisis (2) – and treat prostate cancer (3).

Vitamin K deficiency is unusual as only small amounts are required. 1µg per kg of body weight is the recommended daily intake (one cup of kale contains 317µg). However, as it is fat soluble, a diet very low in fats can cause problems. Taking broad spectrum antibiotics can reduce vitamin K in the gut by up to 74%. Patients with chronic kidney disease can also be deficient.

What exactly is a vitamin?

Definition: Any of a group of organic compounds which are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be synthesized by the body.

Origin: early 20th century: from Latin vita ‘life’+ amine, because vitamins were originally thought to contain an amino acid.

Oxford Dictionary

Home-grown Kale

Sources of vitamin K1

Vitamin K1 – also known as phylloquinone – is made by plants. It’s found in highest amounts in green leafy vegetables – notably kale – because it’s directly involved in photosynthesis.

Below are the 10 best natural sources of K1

Sources of Vitamin K

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Sources of vitamin K2

Vitamin K2 – also known as menaquinone – is mostly found in animal products, and can also be produced by healthy gut flora. The best known vegan source is fermented soy.

There’s some debate over the required levels of K2 in the diet. K1 is understood to convert to K2 quite readily in animals, but perhaps not so readily in humans (4).


A brief history of vitamin K

Henrik Dam wanted to know whether chicks could synthesise cholesterol. Don’t ask why. He knew rats, mice and dogs could, but some experiments with chicks showed they did not thrive on a diet free from cholesterol. Henrik fed chicks with cholesterol-free food and added vitamins A and D to see if that helped. He found that the chicks were actually synthesising cholesterol but many of them developed haemorrhages.

At this point we have to believe that a number of chicks were sacrificed in the course of these experiments and can safely assume that Henrik was not a vegan.

Other researchers had found that if fresh cabbage leaves were added to the cholesterol-free diet, this haemorrhaging did not occur. They thought vitamin C was the key, but when Henrik added pure vitamin C to his chicks’ food the haemorrhaging still occurred. He realised a yet unknown substance was at play.

To cut a long story short, Henrik eventually isolated this substance, which was a vitamin. When his discovery was reported in a German journal, it was described as the koagulationsvitamin, so became vitamin K.

Henrik wondered if this new discovery could be helpful for humans. Vitamin K treatment turned out to be very useful in keeping excessive bleeding under control during some operations, but the most significant area was in the case of newborn babies. Babies sometimes died in the first few days after birth from haemorrhaging. An injection of vitamin K soon after birth cut this figure down dramatically. This is still common practice. Thanks, Henrik.

Henrik received the Nobel prize for medicine jointly with Edward Doisy in 1943 for their work on vitamin K. [Download Source PDF]

Got any tips or questions of your own about vitamin K? Leave us a comment below, we’d love to hear from you.


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