What is vitamin K? How K1 and K2 differ and what the body needs them for

September 28, 2026approx. 15 minutesby mybody®x Editorial & Expert Team

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What is vitamin K?

Vitamin K is not a single substance, but a collective term for several compounds (DGE, 2000). The best known are plant-based vitamin K1 and the vitamin K2 compounds found in animal-based and fermented foods.

Perhaps you saw vitamin K listed on a package next to vitamin D, or heard it mentioned in a conversation about blood thinners. The letter stands for more of a family name than a single vitamin: its members are related, but differ in their origins and structures.

The DGE identifies two groups. Vitamin K1 is chemically called phylloquinone and comes from plants. Vitamin K2 is a whole family of compounds called menaquinones, which are found in animal-based and fermented foods (DGE, 2000). Here, fermented means that bacteria were involved in making the food, as with cheese or sauerkraut (Walther et al., Advances in Nutrition, 2013).

Vitamin K is absorbed in the intestine in the same way as dietary fat (Walther et al., Advances in Nutrition, 2013). How much is absorbed varies greatly. The DGE attributes the very different absorption rates partly to the food matrix, meaning a food’s structure and fat content, and partly to the length of the side chain, a part of the molecule that differs between the compounds (DGE, 2000).

Important doesn’t mean scarce. The fact that your body needs vitamin K doesn’t tell you whether you’re deficient or whether you should take a supplement. Deficiency is rare in healthy adults (MSD Manual, 2024). So whether you need extra depends not on the vitamin, but on your situation.

Vitamin K1 and K2: What’s the difference between the two forms?

K1 and K2 differ mainly in where they come from and how long they remain in the blood. The K2 form MK-7 stays in the blood considerably longer than K1 (Schurgers et al., Blood, 2007).

Schurgers and Vermeer found vitamin K1 mainly in green vegetables and plant-based margarine. K2 was found in animal foods such as liver or egg yolk, and in fermented foods such as cheese or natto, a dish made from fermented soybeans (Schurgers & Vermeer, Haemostasis, 2000).

Menaquinones are abbreviated as MK followed by a number; forms from MK-4 to MK-10 have been found in foods (Walther et al., Advances in Nutrition, 2013). MK-4 is an exception because bacteria do not produce it. Humans and animals produce it themselves, as certain tissues convert K1. In fermented dairy products, by contrast, MK-8 and MK-9 predominate; these are produced by bacteria (Walther et al., Advances in Nutrition, 2013).

The different forms behave differently in the blood. In a small study of six healthy men, K2 levels in the blood were about ten times higher after 200 g of natto than K1 levels after 400 g of spinach (Schurgers & Vermeer, Haemostasis, 2000). With six participants, this is an indication, not proof.

Schurgers and colleagues found a key difference in the half-life, the time it takes for half of a substance to disappear from the blood. MK-7 has a very long half-life, so its levels remain much more stable than those of K1. With longer-term intake, MK-7 levels in the blood rose to seven to eight times higher (Schurgers et al., Blood, 2007).

How much K1 and K2 individual foods provide is shown in the vitamin K food table: it lists the amounts per food and serving; here, the focus is on the basics.

K1 and K2 compared

Table sources: DGE, 2000; EFSA, 2017; Schurgers & Vermeer, 2000; Schurgers et al., 2007; Walther et al., 2013

What does vitamin K do in the body?

Vitamin K is a cofactor, meaning an aid the body needs to produce certain proteins: clotting factors in the liver, osteocalcin in bone, and matrix Gla protein in cartilage and the blood vessel wall (Schurgers et al., Blood, 2007).

You can think of a cofactor as a tool a workshop needs for a particular task. Clotting factors are proteins in the blood that cause it to clot at a wound and stop the bleeding. Osteocalcin and matrix Gla protein are proteins outside the liver: one is found in bone, the other in cartilage and the blood vessel wall (Schurgers et al., Blood, 2007).

There is a difference between these proteins. In healthy people under normal conditions, clotting factors are virtually all in their active form. By contrast, 10 to 40% of osteocalcin and matrix Gla protein remain inactive (Theuwissen et al., British Journal of Nutrition, 2012).

The article on vitamin K and blood clotting answers whether vitamin K2 makes blood thicker or thinner. For bones, the DGE states that vitamin K is important for bone metabolism (DGE, 2000). What additional vitamin K does for bones and blood vessels is a different question, and the studies on this are less clear-cut.

What is the daily requirement for vitamin K?

For adults, the DGE recommends 60 to 80 µg of vitamin K per day, depending on age and sex (DGE, 2000). The EFSA sets 70 µg of vitamin K1 per day for all adults (EFSA, 2017).

Both figures are estimated values. An estimated value describes what an expert organization considers an adequate intake; it is not a recommendation in the strict sense (DGE, 2000). The values apply to intake over the whole day; they are not a recommendation to take a supplement.

The DGE differentiates by age and sex. For men aged 15 to under 51, it gives 70 µg per day, and 80 µg from age 51 onward. For women of the same ages, the figures are 60 µg and 65 µg from age 51 onward (DGE, 2000). There are separate, lower values for infants and children. The table does not distinguish between K1 and K2 (DGE, 2000).

The EFSA takes a different approach. It sets an estimated value only for K1: 1 µg per kilogram of body weight per day, or 70 µg per day for all adults; this explicitly also applies to pregnant and breastfeeding women (EFSA, 2017). It adopted this value from the EU’s former Scientific Committee for Food in 1993 (EFSA, 2017).

Estimated values for adults

Source: German Nutrition Society, 2000; EFSA, 2017

The EFSA does not set a separate value for K2 because it considers the data on menaquinones insufficient (EFSA, 2017). It is therefore not possible to compare the amount of K2 listed on a package with any reference value specifically for K2.

Vitamin K and bones: What do the studies show?

The evidence is still inconclusive: An analysis of 36 studies found no effect on bone density, meaning the mineral content of bone, and suggested that fewer fractures overall may be possible, but this has not been confirmed (Mott et al., Osteoporosis International, 2019).

There is no doubt that bones need vitamin K. Whether additional vitamin K prevents fractures is not established. A deficiency can weaken bones (MSD Manual, 2024), but that does not mean that more vitamin K provides additional benefits when intake is adequate.

Mott and colleagues conducted a meta-analysis, an analysis that combines the results of several studies. It included randomized studies, in which chance determines who receives vitamin K and who does not. For people after menopause or with osteoporosis, a disease involving pathological loss of bone mass, there was no evidence of an effect on bone density or vertebral fractures. There were too few studies for other groups (Mott et al., Osteoporosis International, 2019).

The result for fractures overall was more favorable, but not robust. The odds ratio, a comparative measure where any value below 1 means fewer fractures in the vitamin K group, was 0.72. When only studies with a low risk of bias were counted, it was 0.76, and the uncertainty range extended to 1.01, meaning it went above 1, the value indicating no difference. For vertebral fractures, it was 0.96 (Mott et al., Osteoporosis International, 2019).

A second meta-analysis found more favorable figures. Salma and colleagues analyzed 20 studies and found odds ratios of 0.42 for vertebral fractures and 0.44 for fractures overall (Salma et al., Biomedicines, 2022). For vertebral fractures, this conflicts with the analysis by Mott and colleagues. Salma and colleagues also consider the evidence insufficient for bone density at the femoral neck (Salma et al., Biomedicines, 2022).

Two analyses, two results. The more extensive analysis, with 36 studies, is the benchmark here (Mott et al., Osteoporosis International, 2019); the analysis with 20 studies is presented alongside it as a differing finding (Salma et al., Biomedicines, 2022).

Vitamin K and vascular calcification: What is proven?

There is evidence of less calcification, but no proven benefit. A meta-analysis of 13 controlled studies, meaning studies with a comparison group, found 9.1% less vascular calcification with vitamin K, but no reduction in vascular stiffness (Lees et al., Heart, 2019).

Vascular calcification refers to calcium deposits in the walls of blood vessels; vascular stiffness describes how inelastic those walls are. In the analysis by Lees and colleagues, involving 2,162 participants, calcification decreased, but stiffness did not (Lees et al., Heart, 2019). The authors themselves note the limitations: there were few studies, and they differed greatly from one another.

The studies measured surrogate markers, meaning measurements such as calcium in the vessel wall that stand in for the condition of blood vessels (Lees et al., Heart, 2019). These values provide no more than an indication.

A second meta-analysis of 14 randomized studies involving 1,533 participants mainly examined patient groups, including people with kidney disease (Li et al., Frontiers in Nutrition, 2023). Adverse events did not differ between the groups. In the authors’ view, only more carefully designed studies can show whether vitamin K actually slows vascular calcification (Li et al., Frontiers in Nutrition, 2023).

These results cannot be readily applied to healthy people with no pre-existing conditions. Anyone with a pre-existing condition should discuss vitamin K with their primary care doctor first.

What happens when vitamin K is lacking?

The main sign of vitamin K deficiency is bleeding, such as bruising under the skin or bleeding from the nose (MSD Manual, 2024). Deficiency is rare in healthy adults (MSD Manual, 2024).

The MSD Manual, a medical reference work, explains that “many green vegetables contain vitamin K, and bacteria in the gut also produce vitamin K” (MSD Manual, 2024). Even so, levels can become low. A review notes that a subclinical deficiency, meaning one without visible signs, can be triggered simply by limiting K1 intake (Walther et al., Advances in Nutrition, 2013).

Newborns are an exception. According to the DGE, breastfed infants are at risk of vitamin K deficiency, so vitamin K is given preventively shortly after birth to protect against bleeding tendencies (DGE, 2000).

The article Vitamin K deficiency: symptoms and causes describes other signs that may indicate a deficiency and the possible underlying causes. The MSD Manual lists causes such as a very low-fat diet or diseases that interfere with fat absorption (MSD Manual, 2024). Anyone who notices unusual bruising or bleeding should first have it checked at their primary care practice; in the event of severe bleeding, call 112.

A special case is anticoagulants known as vitamin K antagonists, meaning medications that counteract vitamin K, such as those containing the active ingredients phenprocoumon or warfarin. MK-7 supplements can interfere with their effects in a clinically significant way (Schurgers et al., Blood, 2007). Anyone taking these medications should discuss any questions about vitamin K with their treating doctor.

Vitamin K from food or as a dietary supplement?

The main source of vitamin K is food. The DGE names green vegetables such as spinach and some types of cabbage as especially good sources (DGE, 2000).

On the animal-based side, it lists milk and dairy products as well as meat and eggs (DGE, 2000). Since vitamin K is best absorbed with some fat (MSD Manual, 2024), feel free to serve the vegetables with oil or cheese.

The article on vitamin D3 and K2 combined explains why supplements combine vitamin K2 with vitamin D3 and what can be measured for each.

Those considering a supplement can find the Vitamin D3 K2 Complex Shield from mybody®x (MYBODY Lab GmbH), a dietary supplement containing vitamin D3 and vitamin K2. mybody®x does not offer a test that measures vitamin K. The Shield does not answer the open questions about bone fractures and vascular calcification. Anyone taking blood thinners should discuss it with their healthcare provider first.

Do you need extra vitamin K?

It depends on your situation, not the vitamin: deficiency is rare in healthy adults (MSD Manual, 2024).

Things are different when medication is involved. The MSD Manual lists antiepileptic drugs, meaning medication for epileptic seizures, and some antibiotics among the possible causes of a deficiency (MSD Manual, 2024). If you take such medications or blood thinners, your healthcare provider is the first person to ask about vitamin K.

For everyone else, the question can be reduced to what’s on your plate. If your diet includes green vegetables and animal products such as dairy or eggs, you’re getting the sources the DGE lists as good suppliers (DGE, 2000). Whether additional vitamin K does anything more for bones or blood vessels remains unclear based on the studies.

Vitamin K is a family name for several compounds your body needs for blood clotting and bones. Whether you need anything beyond that depends on your situation, not the packaging, and if in doubt, talk to your healthcare provider.

Frequently asked questions

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Sources

1. German Nutrition Society: Reference Values for Nutrient Intake, Vitamin K (as of 2000) – dge.de
2. EFSA NDA Panel: Dietary Reference Values for vitamin K, EFSA Journal (as of 2017) – europepmc.org
3. Schurgers et al.: K1 and MK-7 compared, Blood (as of 2007) – europepmc.org
4. Mott et al.: Vitamin K and bones, Osteoporosis International (as of 2019) – europepmc.org

[1] supports the DGE citation and estimates, [2] the EFSA estimate for K1. [3] covers the functions of vitamin K and the time MK-7 remains in the body, [4] the evidence on bones. The other studies are cited in the text at their respective sources by author and year, as is the MSD Manual. Product information as of 28.09.2026; sources checked on 28.09.2026.