How to take the right dose of vitamin K2? A practical guide

Vitamin K was first described in the first half of the 20th century, when, between 1928 and 1930, Henrik Dam investigated blood clotting disorders in animals fed a diet lacking certain fatty acids. Nowadays, the term "vitamin K" refers to vitamin K1 (phylloquinone) and vitamin K2 (a group of menaquinones with different structures). When determining the dosage, the sources of vitamin K chosen, age, health status, medications taken and the use of supplements are all important factors.

1. Foods containing vitamin K
2. MK abbreviations – what do they mean?
3. Vitamin K requirements
4. Vitamin K dosage

Foods containing vitamin K

Vitamin K occurs in food in several forms, so before discussing dosage, it is worth first distinguishing between its main sources. Vitamin K1, or phylloquinone, is primarily found in plant-based foods, particularly green leafy vegetables. Kale, spinach, parsley, lettuce, rocket, savoy cabbage, broccoli and Brussels sprouts, amongst others, can play a significant role in the diet. It is these foods that are usually the primary source of the total vitamin K intake in the daily diet.

MK abbreviations – what do they mean?

Vitamin K2, on the other hand, comprises menaquinones, denoted by the abbreviations MK, for example MK-4, MK-7, MK-8 and MK-9. Individual menaquinones differ in the length of their side chains, and in dietary practice also in their typical sources. MK-7 is particularly often associated with natto, i.e. fermented soya, and with dietary supplements. Certain mature cheeses can provide menaquinones such as MK-8 and MK-9, although their content depends on the type of cheese, the bacterial cultures used and the maturing conditions. MK-4 may be present in small amounts in animal-derived products, including meat, eggs, butter and offal. However, the vitamin K2 content in such products is not consistent.

"Although there are currently no official guidelines on how often to eat fermented foods, adding a few portions to your diet may be beneficial. For best results, start by eating one or two portions a week, then slowly increase the amount." Łukasz Domeracki – Dietitian

Vitamin K requirements

In accordance with the 2024 Polish dietary reference values for the Polish population, the reference values for vitamin K have been set at the adequate intake (AI) level and are expressed in micrograms of phylloquinone per person per day.

Children and adolescents

For infants from 6 to 12 months of age, this value is 8.5 µg per day. For children, the recommended intake is 15 µg for ages 1–3 years, 20 µg for ages 4–6 years, and 25 µg for ages 7–9 years. For boys, the recommended intake rises to 40 µg for ages 10–12, 50 µg for ages 13–15 and 65 µg for ages 16–18, whilst for girls it is 40 µg, 50 µg and 55 µg per day respectively.

Adults and pregnant women

For adult men, regardless of age group from 19 years of age to over 75 years of age, the recommended daily intake is 65 µg of vitamin K. For adult women aged 19 to over 75, the recommended daily intake is 55 µg. The same value, i.e. 55 µg per day, is also specified for pregnant women and breastfeeding women. Food and supplement labels may also feature the RDA, or Recommended Daily Allowance. According to the European Union, this is 75 µg for vitamin K, so a preparation containing 75 µg of vitamin K provides 100% of the RDA.

Estimates of vitamin K content in selected food products

Vitamin K dosage

In dietary supplements, vitamin K2 is most commonly found as MK-7, and less frequently as MK-4, usually in capsules, tablets, drops or oil-based preparations. Correct dosing depends primarily on adjusting the dose to the individual’s age, their total dietary intake of vitamin K, and the concurrent use of other supplements. In practice, MK-7 is often used in microgram doses, for example 25, 50, 75, 100 or 200 µg per daily dose.

Before starting supplementation, it is therefore advisable to calculate the total amount of vitamin K from all sources and not to exceed the dose recommended by the manufacturer, unless a different dose has been prescribed by a doctor or pharmacist. Particular caution is required for people taking anticoagulants, especially vitamin K antagonists, as the sudden introduction, discontinuation or significant change in the dose of vitamin K may affect the course of treatment. Consultation with a doctor or pharmacist is also recommended during pregnancy, while breastfeeding, in children, in cases of chronic illness, prior to medical procedures, and when several medicines or supplements are being taken simultaneously.

Sources:

• 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
• Booth S. L. (2012). Vitamin K: food composition and dietary intakes. Food & nutrition research, 56, 10.3402/fnr.v56i0.5505. https://doi.org/10.3402/fnr.v56i0.5505
• Violi, F., Lip, G. Y., Pignatelli, P., & Pastori, D. (2016). Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True?: A Systematic Review. Medicine, 95(10), e2895. https://doi.org/10.1097/MD.0000000000002895