Vitamin K: The Forgotten Vitamin

Nothing increases appeal like an air of mystery. And no-one is more specialised in mystery than vitamin K. Sometimes referred to as ‘the forgotten vitamin’, it continues to keep its secrets. Next to its known involvement in blood clotting and bone formation, studies from the last decade are starting to connect it more and more with cognitive health and even a potential role in the prevention of Alzheimer’s disease.

Let’s review the most important findings about vitamin K so far.

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Types: Vitamin K, Vitamin K1 (phylloquinone), Vitamin K2 (menoquinone)

Best known for: Blood clotting and bone metabolism; keeping the central nervous system healthy; preventing vascular calcification (‘stiffening’ of your arteries).

Good sources: Green leafy vegetables (vitamin K1), fermented food and animal products (vitamin K2). K2 is also produced by gut bacteria in the body.

Adequate intake (AI): 70 mcg per day. No tolerable upper intake level (UL) has been established.

Good to know: Vitamin K1 is absorbed up to twenty times better when consumed in pure form, as a tablet, than when consumed through food.

Vitamin K in Jake:
Jake Light and Original: 33% of AI
Jake Sports: 25% of AI
Vitaminbars: 25% of AI

What is vitamin K?

Vitamin K is a fat-soluble vitamin Vitamins can be fat-soluble and water-soluble. Vitamin K is fat-soluble. This means that it is absorbed with the help of lipids (fats) and is less likely than water-soluble vitamins (like B and C) to leave the body through the kidneys. with two vitamersVitamers are chemical compounds with a similar molecular structure, which fulfil the same function in the body. – K1 and K2, a.k.a. phylloquinone and menaquinone. Both can be found in food. The major difference is that K2 is also produced in the body by gut bacteria.To be exact, there is also a third form of vitamin K, known as K3 or menadione. It is a synthetic type of vitamin K and has been banned by the US Food and Drug Association (FDA) for use in human food, due to its potential toxicity. Small doses that are considered safe continue to be used in some pet foods and livestock feed.Source: U.S. Food & Drug Administration

Health benefits of vitamin K

The role of vitamin K in your body is best summarised as supporting, but vital. Vitamin K acts as a coenzymeEnzymes are substances, mostly proteins, that speed up biochemical reactions within the body. A coenzyme is a substance that helps enzymes do their job.. It partners with proteins and ensures their biological activation – the process which allows them to perform their function in the body.

Most notably, the functions that depend on vitamin K are:

  • Blood coagulation (clotting): The process of transforming blood from a liquid to a gel as a start of the healing process after injury.
  • Bone metabolism: The continuous replacement of mature bone tissue with new bone tissue.
  • The prevention of vascular calcification: A process by which soft tissue (including arteries) loses elasticity, increasing the likelihood of coronary heart disease.
  • The functioning of the central nervous system, including neuronal survival (and, thus, cognitive function).This role of vitamin K in cognitive health is among the most recent focus areas for research, with some studies pointing to an association between higher concentration of vitamin K1 in the blood and better performance in verbal memory tests by elderly individuals. This opens the door for further exploration of a potential role vitamin K could play in the prevention and alleviation of Alzheimer’s disease.Source: Vitamin K and Vitamin K-Dependent Proteins in Relation to Human Health

Some studies, mostly done in animals, point out a potential role vitamin K could play in cancer treatment. It has been demonstrated to inhibit cancer cell growth and help suppress inflammationSource: Alternative Medicine Review, either alone or through proteins it activates. However, far more evidence is needed before vitamin K’s potential anticancer properties are understood and confirmed.

Vitamin K can be applied directly to the skin to help reduce bruising after injury. Ointments with a high concentration of vitamin K (e.g. 5%) are most effective.

How much vitamin K do you need?

Currently, there are insufficient data to determine a recommended dietary allowance (RDA)Recommended Dietary Allowance (RDA) is the average daily intake sufficient to meet the nutritional requirements of 97%-98% of healthy individuals. for vitamin K. However, the European Food Safety Authority (EFSA) has indicated that 70 micrograms per day is an adequate intake (AI)Adequate Intake (AI) is the amount assumed to meet the nutritional requirements of an average healthy individual. It is used when no RDA has been established for a specific nutrient.. Think of it as ten lettuce leaves or 1/8th of a cup filled with spinach.

Vitamin K in foods

Both vitamin K1 and K2 function in the same way but are active in different parts of your body. Vitamin K1 dissolves relatively easily and is mostly found in the liver where proteins responsible for blood-clotting are made. Vitamin K2 is more abundant in fatty tissues, as well as bones and our brains. It is, therefore, important to ensure that both are present in your diet.

The best food sources of Vitamin K1 are green leafy vegetables and vegetable oils. To a lesser extent, it can also be found in dairy, meat and eggs. These animal sources provide a relatively high amount of vitamin K2, whereas plant sources mostly provide vitamin K1. Vitamin K2 is also abundant in many fermented foods, such as cheese, yoghurt or fermented soybeans (a.k.a. the Japanese “natto” dish).

These are the top sources of vitamin K:

FoodAI (%)*Vitamin K1 (mcg)
Kale (100 g)1167%817
Turnip greens (100 g)524%367
Spinach, raw (100 g)563%394
Endive (100 g)330%231
Lettuce (100 g)185%129


FoodAI (%)*Vitamin K2 (mcg)
Natto (100 g)1107%775
Semi-skimmed cottage cheese (200 ml)71%50
Parmesan (15 g)16%11
Gouda cheese, 48+ (per slice)14%10

* Based on the adequate intake (AI) established by EFSA.

Vitamin K1 is absorbed significantly better when consumed in pure form (e.g. as a dietary supplement) than when consumed through food. For example, the amount of K1 you absorb from a tablet could be up to twenty times more than that from spinach.
TIP: To improve the absorption rate of K1 from vegetables, consume them together with some fats.

What if you’re not getting enough vitamin K?

Not enough vitamin K in your diet can have several consequences. Most prominently, these include increased vascular calcification Calcification is the process by which calcium builds up in body tissues, blood vessels and organs. As a result of calcification, they stiffen and their normal functioning is disrupted. When this happens in your arteries, it is called vascular calcification., risk of coronary heart disease and reduced bone density which may contribute to osteoporosis. Additionally, recent studies suggest that lower availability of vitamin K may be associated with cognitive impairment among the elderlySource: Vitamin K and Vitamin K-Dependent Proteins in Relation to Human Health.

Severe cases of vitamin K deficiency become apparent via a significant increase in the time needed for blood to clotThe time needed for blood to clot is called ‘prothrombin time’.. This can lead to incessant bleeding and haemorrhage. The good news is, such extreme cases are very rare, especially among adults with a varied diet.

However, there are some groups at risk, including:

  • Babies: Especially during the first weeks of life, babies are vulnerable to vitamin K deficiency. This is due to the low transfer of K1 from the mother via the placenta and the low content of vitamin K in breast milk. To avoid complications and possible fatalities, babies in many countries are injected with a high dose of vitamin K1 at birth. There has been some concern with regards to possible negative reactions caused by vitamin K1 shots in new-borns. This is mostly due to the warning label on the injection package, quoting potentially fatal negative reactions. This is scary to read as a parent but needs to be put in context before making a decision to refuse the shot for your baby. Even though adverse and, sometimes, fatal reactions to a vitamin K1 injection can occur, they are considerably more common when the shot is administered in the veins as compared to the muscles. New-borns always receive their vitamin K1 shot in the muscles, which ensures slower absorption and minimises the risk of complications. Only very few casesSource: The Journal of Maternal-Fetal & Neonatal Medicine of negative reaction following a K1 shot in babies have actually been reported. On the scale of new-borns worldwide who are injected with vitamin K daily, the number of reported complications is statistically insignificant.
    At the same time, administering the vitamin K1 shot at birth saves lives. European data show that incidence of vitamin K deficiency bleeding (VKDB) among children who got the vitamin K1 injection at birth is as low as 0 to 0.62 cases per 100,000. Without the shot, these cases would be close to 6,000.The mortality rate of VKDBSource: Blood Transfusion Journal can be as high as 20% and close to 40% of surviving children suffer from long-term brain damage.
  • Adults who suffer from malabsorption disorders or those who are taking drugs which interfere with the absorption or activity of vitamin K. Such drugs include anticoagulants, as well as some antibiotics that kill vitamin K-producing bacteria in the gut. Another example are weight loss drugs that reduce the absorption of dietary fat and, as a consequence, of fat-soluble vitamins like vitamin K.

How much vitamin K is too much?

Overconsumption of vitamin K is actually not something to worry about under normal circumstances. There are no known side effects of consuming excessive amounts of either vitamin K1 or K2.


Despite being nicknamed ‘the forgotten vitamin’, don’t forget about vitamin K. Or at least try and remember these few things:

  • It’s involved in more than just blood clotting.
  • From the renewal of bone matter to the elasticity of your arteries and the functioning of your brain, it is behind many key functions in your body.
  • If you don’t get enough vitamin K, you might not notice it until much later. However, inadequate intake can contribute to serious illnesses over time, including osteoporosis and coronary heart disease.
  • You can find vitamin K in green leafy vegetables, dairy products and fermented foods such as cheese and yoghurt. If you are vegetarian, it’s best to eat vitamin K-rich vegetables together with some fats (e.g. nuts) for better absorption.

Questions? Do let us know.