Vitamins K1 and K2 – how do they differ?

In 1954, warfarin – which is still used in medicine today – was approved as an anticoagulant. It works by limiting the body’s reutilisation of vitamin K. Demonstrating this relationship has led to a better understanding of the role of vitamin K in the normal course of blood clotting processes. Subsequent research has also shown that it plays a part in the activation of proteins found in bone tissue. In food and supplements, vitamin K occurs in several different forms, including K1 and K2.

1. Sources of vitamin K in the diet
2. Characteristics of vitamins K1 and K2
3. The amount of vitamin K in the diet
4. FAQ

Sources of vitamin K in the diet

Vitamin K is a nutrient required for day-to-day functioning, even in small amounts. The body uses it to activate specific proteins which, without it, would be unable to perform their functions properly. Some of these proteins are involved in the blood-clotting process, whilst others are found in bone tissue.

The main sources of vitamin K are dark green leafy vegetables, including kale, spinach, lettuce and parsley, as well as broccoli, cabbage and Brussels sprouts. Smaller amounts are found in vegetable oils, meat, offal, eggs and dairy products. Vitamin K is also found in certain fermented foods, particularly cheese and natto (fermented soya). Some of the compounds that make up vitamin K are produced by gut bacteria, but it is not possible to determine exactly to what extent they meet a person’s requirements.

As vitamin K is fat-soluble, its absorption requires bile, digestive enzymes and the presence of fat in the digestive tract. Adding a small amount of oil, seeds, nuts or another source of fat to vegetables increases its absorption. Deficiency is rare in healthy people who eat a varied diet, but the risk may increase in cases of fat malabsorption, liver or biliary tract diseases, and when taking certain medicines.

Characteristics of vitamins K1 and K2

Vitamin K1, known as phylloquinone or phytomenadione, is produced by plants and is the main form of vitamin K in the average diet. The green parts of plants are the richest sources, as this compound is involved in the processes that take place during photosynthesis.

Vitamin K2 is not a single substance, but a group of menaquinones designated by the symbols MK-4 to MK-13. The number indicates a difference in the molecule’s structure, which affects, amongst other things, how long it remains in the blood. MK-4 is found mainly in animal-derived products and can also be produced in the body from vitamin K1. MK-7 is found primarily in natto and other fermented products, whilst cheeses may also contain MK-8 and MK-9.

All these forms are involved in the same basic process of activating vitamin K-dependent proteins; therefore, one should not attribute K1 exclusively to blood clotting, nor K2 exclusively to bone health. The differences relate primarily to sources, transport and the duration of circulation.

K1 is rapidly taken up by the liver, whilst long-chain menaquinones, particularly MK-7, remain in the blood for longer. However, this does not mean that every form of K2 is always absorbed more effectively than K1. Approved health claims refer to vitamin K as a group, rather than to the superior efficacy of any one of its forms.

Estimated vitamin K1 and K2 content in selected foods (µg/100 g)

The amount of vitamin K in the diet

In 2017, the European Food Safety Authority set the adequate intake of vitamin K at approximately 1 µg per kilogram of body weight per day. For infants aged 7–11 months, this is 10 µg; for children aged 1–3 years, 12 µg; for those aged 4–6 years, 20 µg; for those aged 7–10 years, 30 µg; for those aged 11–14 years, 45 µg; and for adolescents aged 15–17 years, 65 µg per day. For adults, the recommended intake is 70 µg per day, regardless of gender. These are adequate intake values, rather than classic average requirement standards, as the available data did not allow for a precise determination of the average requirement. European standards were established on the basis of phylloquinone, as there was insufficient data on the intake, absorption and utilisation of menaquinones.

In multivitamin preparations and ADEK-type products, vitamin K is usually present as K1 or K2 in amounts of around 25–75 µg. In single-ingredient supplements and combinations with vitamin D, K2 in the form of MK-7 is most commonly used, usually at a dose of 75, 100 or 200 µg per daily serving. It is available in tablets, capsules, drops and oil-based capsules.

"Vitamins K1 and K2 do not function as two separate vitamins. Both are involved in the activation of the same vitamin K-dependent proteins, and differ primarily in their sources, chemical structure and how long they remain in the body. From a health perspective, the most important thing is to ensure an adequate supply of vitamin K from your daily diet, rather than seeking out a single ‘best’ form of it." Łukasz Domeracki – Dietitian

FAQ

Is vitamin K1 better than K2?

It cannot be definitively stated that one form is better than the other. Both vitamin K1 and K2 play a role in the activation of vitamin K-dependent proteins. They differ mainly in their sources, structure and how long they remain in the body.

Does vitamin K2 only affect bones?

No. This is a common myth. Both vitamin K1 and K2 play a role in the same fundamental biological processes. One should not attribute blood clotting solely to K1, nor bone health solely to K2.

Where is vitamin K1 found in greatest quantities?

The richest sources of vitamin K1 are green leafy vegetables, such as kale, spinach, parsley, lettuce, Swiss chard and broccoli.

In which foods is vitamin K2 found?

Vitamin K2 is found primarily in fermented foods, particularly natto, as well as in certain cheeses, meat, eggs and dairy products. Small amounts can also be produced by gut bacteria.

Should vitamin K be taken with fat?

Yes. Vitamin K is fat-soluble, so it is absorbed more effectively when a meal contains a small amount of healthy fats, such as olive oil, nuts, seeds or avocado.

Can people taking anticoagulants take vitamin K?

People taking vitamin K antagonists, such as warfarin or acenocoumarol, should not start taking supplements on their own. A sudden increase or decrease in vitamin K intake may affect the effectiveness of their treatment, so any changes to their diet or supplementation should be discussed with their doctor.

Is vitamin K2 MK-7 more easily absorbed than K1?

Research shows that long-chain menaquinones, such as MK-7, remain in the blood for longer than vitamin K1. However, this does not mean that they are unequivocally "more easily absorbed" or more effective. The health claims currently approved by the EFSA relate to vitamin K as a whole, rather than to the superiority of any specific form.

Sources:

• Shearer, M. J., & Newman, P. (2014). Recent trends in the metabolism and cell biology of vitamin K with special reference to vitamin K cycling and MK-4 biosynthesis. Journal of lipid research, 55(3), 345–362. https://doi.org/10.1194/jlr.R045559
• Schurgers, L. J., Teunissen, K. J., Hamulyák, K., Knapen, M. H., Vik, H., & Vermeer, C. (2007). Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood, 109(8), 3279–3283. https://doi.org/10.1182/blood-2006-08-040709
• EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), Turck, D., Bresson, J. L., Burlingame, B., Dean, T., Fairweather-Tait, S., Heinonen, M., Hirsch-Ernst, K. I., Mangelsdorf, I., McArdle, H. J., Naska, A., Nowicka, G., Pentieva, K., Sanz, Y., Siani, A., Sjödin, A., Stern, M., Tomé, D., Van Loveren, H., Vinceti, M., … Neuhäuser-Berthold, M. (2017). Dietary reference values for vitamin K. EFSA journal. European Food Safety Authority, 15(5), e04780. https://doi.org/10.2903/j.efsa.2017.4780