• by: Fondazione Valter Longo
  • April 6th, 2022

Vitamin K is part of the group of fat-soluble vitamins. Vitamin K refers to three different compounds called naphthoquinones, which are similar to each other but with different structures and molecular properties. K1 (phylloquinone) is the natural form of vitamin K. It is found in plants and can be assimilated through the diet. K2 or MK (menaquinone) consists of various compounds synthesized by the bacterial flora in the intestine, which provides the body with a low amount compared to its needs. K3 (menadione) of synthetic origin is present in vitamin supplements, which unlike the other forms is also water-soluble.


Vitamin K is useful for some important processes in our body. For example, it takes part in blood coagulation, and it has an anti-hemorrhagic action. Vitamin K, in fact, participates in the synthesis of essential substances to produce blood-clotting factors (prothrombin, factors VII, IX, and X) and anticoagulant enzymes (proteins C, S, and Z).

Vitamin K performs other functions, thanks to the regulation of enzymes involved in other fundamental processes for the human body. K2, for example, comes into play in calcium homeostasis and bone mineralization, as well as in cartilage and artery wall formation. Together with calcium and vitamin D, vitamin K is therefore useful for treating bone fractures and preventing osteoporosis.


The recommended daily intake varies according to age, gender, weight, and condition. For example, adults need about 1 µg per kg/2.20 lbs. of body weight per day of vitamin K. This quantity is usually guaranteed by a varied and balanced diet and by the endogenous production of the bacterial flora.

The deficiency of this vitamin, therefore, is hardly linked to nutrition. However, vitamin K deficiency can be caused by gastrointestinal diseases (malabsorption, Crohn’s disease, etc.), other conditions limiting fat absorption in the intestine (including alcohol abuse), and prolonged use of antibiotics or anticoagulants (molecules antagonists to this vitamin). In these cases, vitamin K deficiency can lead to bleeding due to inadequate synthesis of clotting factors.

Furthermore, according to some scientific research, there seems to be a relationship between low levels of vitamin K2 in the blood and the risk of fractures and osteoporosis. Vitamin K2, in fact, acts synergistically with vitamin D in supporting bone density. 


Vitamin K1 is mainly found in green leafy vegetables (such as spinach, radicchio, rocket, cress, lettuce, broccoli, cauliflower, cabbage, Brussels sprouts, cabbage, turnip greens, radishes, turnips, asparagus, and horseradish), also in legumes (peas, chickpeas, soy, and beans), and olives.

Other sources are fruits such as kiwis and avocados, nuts, and grains.

Among the sources of animal origin, we find the vitamin in its K2 form in meat (liver, cattle, and pork are rich in it), eggs, milk, and dairy products, but in less significant quantities. In addition, tea, both green and black, is rich in vitamin K, while coffee contains a little less.

Examples of food sources of K2 are also fermented dairy products, like cheese and fermented vegetables, such as natto (traditional Japanese food produced by fermenting soybeans) and sauerkraut.

K2 is synthesized by the intestinal bacterial flora. It is therefore important to take care of it with prebiotic foods, rich in non-digestible substances (i.e., fiber) but which help the microbiota (all intestinal microorganisms) to remain healthy.


Vitamin K is not subject to losses during cooking. Therefore, the high heat required to boil vegetables will not decrease vitamin K levels. Also, in this case, it is not possible to provide general instructions for cooking to preserve vitamin K in food. Nevertheless, it is important to reduce cooking times as much as possible, to avoid any harmful burns and the loss of other vitamins present in food.


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  • Vitamine – Studi – EPICENTRO (last viewed 02/07/2022)

  • LARN – Livelli di assunzione di riferimento per la popolazione italiana: VITAMINE. Fabbisogno medio (AR); valori su base giornaliera – Società Italiana di Nutrizione Umana-SINU, 2014 (last viewed 02/07/2022)

  • Vitamin and Mineral Supplement Fact Sheets – NIH National Institute of Health (last viewed 02/07/2022)

  • Vitamin K – NIH National Institute of Health (last viewed 02/07/2022)


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