Calcium and vitamin K2: why K2 gets mentioned
Futures Nutrition Editorial Team · 12 August 2026
Calcium and vitamin K2: why K2 gets mentioned
The short answer: in the EU there is no authorised statement for vitamin K that relates to calcium. The line that K2 steers calcium "into the bones instead of the arteries" describes a hypothesis from basic research — EFSA examined it in 2012 and judged it insufficiently substantiated. What is settled is more modest: calcium and vitamin K both contribute to the maintenance of normal bones, each on its own.
For the purchase decision that makes a difference. Anyone holding a calcium supplement does not need to look for K2 as well so that the calcium "arrives in the right place". The nutrient that actually carries an authorised statement in this context is vitamin D. K2 is a topic of its own, with its own numbers — and with one point that really does matter but is rarely mentioned: the interaction with anticoagulants.
Where the sentence comes from
Vitamin K is a cofactor of an enzyme, gamma-glutamyl carboxylase. This enzyme attaches an additional carboxyl group to certain proteins and only thereby makes them functional. Germany's Federal Institute for Risk Assessment (BfR) describes three processes in which such vitamin-K-dependent proteins take part: blood clotting, bone metabolism and vascular biology.
Two of them are the basis of the popular formulation. Osteocalcin sits in bone and cartilage and is involved in building and regulating the bone matrix. Matrix Gla protein is likewise carboxylated by vitamin K and binds calcium in vascular tissue. The BfR summarises the assumed connection as follows: vitamin D raises the calcium level in serum, among other things through increased absorption in the gut, and vitamin K promotes the flow of calcium from the serum into the bones.
That is a description of a mechanism — not a statement about what a tablet does. This is exactly where advertising copy and the evidence part ways.
What is authorised and what is not
Which statements may be made about nutrients is governed by Regulation (EU) No 432/2012. Every statement is tied to a minimum amount: a food supplement may highlight a nutrient only if it supplies at least 15 per cent of the nutrient reference value per daily portion.
| Statement | Condition per daily portion | Status |
|---|---|---|
| Calcium is needed for the maintenance of normal bones and teeth | at least 120 mg (15 % of 800 mg) | authorised |
| Vitamin K contributes to the maintenance of normal bones | at least 11.25 µg (15 % of 75 µg) | authorised |
| Vitamin K contributes to normal blood clotting | at least 11.25 µg | authorised |
| Vitamin D contributes to normal absorption and utilisation of calcium | at least 0.75 µg (15 % of 5 µg) | authorised |
| Vitamin K2 and the normal function of the heart and blood vessels | — | not authorised |
The last row is the core of this article. The application ran under the identifier ID 125 and was assessed twice, most recently in a dedicated opinion (EFSA Journal 2012;10(6):2714). The result: a cause-and-effect relationship between the intake of vitamin K2 and the normal function of the heart and blood vessels is not established. In its reasoning the panel named four points — human intervention studies were missing, cross-sectional data on arterial calcification in women contradicted each other, prospective cohort studies on the risk of coronary heart disease reached opposing results, and the evidence for the proposed mechanism was weak.
Eleven years later the BfR arrives at the same point and states it unmistakably in the subtitle of its opinion 065/2023: a benefit from combining high-dose vitamin D preparations with vitamin K is not established. To what extent the interaction of the two vitamins has a positive effect on health is currently unclear; there are not enough data for a reliable assessment.
It is striking that the authorised bone statement for vitamin K and the rejected vascular statement are often sold in the same breath. The difference, though, is precisely the one between a checked and an unchecked claim.
The pair that really does belong together
If any nutrient alongside calcium carries its own statement referring to calcium, it is vitamin D. That is why those two sit in one tablet, and not calcium and K2. Our Calcium + Vitamin D3 4,000 IU contains 200 mg of calcium per tablet — 25 per cent of the nutrient reference value — and 100 µg of vitamin D3, but no vitamin K.
Why the two belong together and when one of them is enough is set out in detail in Calcium and vitamin D: why they share a tablet. Anyone additionally taking a preparation with K2 should first add up the vitamin D amounts of both products before looking at the K2 amount — more on that below.
How much K2 actually arrives in everyday life
Vitamin K comes in two families: K1 (phylloquinone) from green leafy vegetables and plant oils, K2 (menaquinones) from fermented and animal foods — matured cheese, quark, meat and above all natto, the Japanese fermented soy dish in the title image. Supplements almost always contain MK-7, a long-chain menaquinone with a half-life of around three days compared with one to two hours for K1.
The German intake data are instructive because they correct two widespread assumptions at once:
| Survey | Group | Median intake |
|---|---|---|
| EPIC cohort Heidelberg | men 40–65 yrs, vitamin K1 | 93.6 µg/day |
| EPIC cohort Heidelberg | men 40–65 yrs, total vitamin K2 | 34.7 µg/day |
| EPIC cohort Heidelberg | men 40–65 yrs, of which MK-7 | 0.8 µg/day |
| Bavarian Food Consumption Survey II | men, vitamin K2 | 37.6 µg/day |
| Bavarian Food Consumption Survey II | women, vitamin K2 | 29.8 µg/day |
First: vitamin K2 is not missing from the German diet, it occurs in orders of magnitude close to the estimated value for vitamin K as a whole. Second: MK-7 of all things, the form found in supplements, hardly occurs in food — 0.8 µg at the median. Anyone taking a tablet with 200 µg of MK-7 is therefore not adding something they eat every day anyway, but two hundred times that amount. That is not an argument against it, but a reason to look at the number deliberately rather than skim past it.
For context, the BfR expressly notes that the German intake estimates are uncertain: the vitamin K content data in the German food database are of low quality, and the National Food Consumption Survey II does not record vitamin K at all.
The numbers on the label
| Reference figure | Vitamin K | Calcium |
|---|---|---|
| Nutrient reference value (label, Regulation (EU) No 1169/2011) | 75 µg | 800 mg |
| D-A-CH estimated value, adults | 60–80 µg | 1,000 mg (DGE) |
| Adequate Intake EFSA (2017) | 1 µg per kg body weight | — |
| Tolerable Upper Intake Level | none derived | 2,500 mg |
| BfR proposal per daily supplement portion | 80 µg K1 or 25 µg K2 | 500 mg |
The second-to-last row is worth a look: for vitamin K the EU's Scientific Committee on Food derived no upper limit, for lack of sufficient data. The available studies point to low acute and chronic toxicity of orally taken vitamin K.
The BfR proposal of 25 µg of K2 therefore has a different reason than a risk of poisoning — it derives entirely from the interaction with anticoagulants (see the next section). It is a proposal, not a limit in force; common preparations such as Vitamin D3 4,000 IU + K2 with 200 µg lie above it. On the safety of these amounts in healthy people the BfR itself cites studies in which MK-7 was given at up to 180 µg daily for three years and up to 360 µg for twelve weeks with no observed adverse effects. Which K2 amount fits which D3 strength is worked through in Vitamin D3 and K2: is there a correct ratio?; further preparations are in the vitamin K2 category.
The point that really counts: anticoagulants
Vitamin K weakens the effect of oral anticoagulants of the coumarin type — the vitamin K antagonists, which act on exactly this metabolic pathway. The BfR quantifies the effect using two studies with twelve healthy participants each, who were set to an INR of 2.0 and then supplemented with increasing doses: the threshold for a statistically detectable lowering of the INR was 150 µg per day for vitamin K1, but 45 µg per day for vitamin K2. K2 is thus around 3.5 times as effective as K1.
For MK-7 the BfR goes further: in people on therapy with vitamin K antagonists, doses below 10 µg of MK-7 per day could already lead to unwanted interactions. The recommendation derived from this is clear — anyone taking anticoagulants uses food supplements containing vitamin K only after consulting a doctor. In healthy people no change in the clotting profile was observed in the same analyses. This is covered in detail in Vitamin K2 interactions: medicines and nutrients.
Calcium has nothing to do with this question. It hangs on the K2 alone — which shows once more that the two nutrients do not form a unit but are two separate decisions.
What this means for the purchase
| Starting point | Sensible consequence |
|---|---|
| calcium supplement, nothing else | K2 is not a prerequisite; the authorised link to calcium belongs to vitamin D |
| calcium + D3 planned, K2 under consideration | a decision in its own right based on the bone statement, not because of the calcium |
| D3+K2 preparation on hand, calcium to be added | first add up the vitamin D amounts of both products, not the K2 amounts |
| anticoagulants of the coumarin type | K2-containing preparations only after consulting a doctor |
| calcium intake from food unclear | estimate first, then supplement — portions and absorption rates are in the food articles |
How to sensibly spread a calcium portion across the day and which intervals apply to other minerals is set out in Taking calcium: dose per serving and spacing. Anyone wanting to look at the combination of D3, K2 and calcium from the other direction will find it in Vitamin K2 and calcium: the combination at a glance.
Among the authorised statements for these nutrients are the following: Calcium is needed for the maintenance of normal bones and teeth. Vitamin K contributes to the maintenance of normal bones. Vitamin K contributes to normal blood clotting. Vitamin D contributes to normal absorption and utilisation of calcium. (Regulation (EU) No 432/2012). Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle.
Frequently asked questions
Do I have to take K2 with calcium? No. There is no authorised statement linking vitamin K to the utilisation of calcium, and the underlying vascular hypothesis was judged insufficiently substantiated by EFSA. The nutrient for which the link to calcium is authorised is vitamin D.
Does calcium end up in the arteries without K2? Put that way, the claim is not established. It rests on the role of matrix Gla protein, that is, on a mechanism. In 2012 EFSA expressly recorded that human intervention studies are missing and that the available observational data contradict each other.
My D3+K2 preparation contains 200 µg of MK-7, the BfR proposes 25 µg. Is that a problem? The BfR figure is a maximum-amount proposal for food supplements and derives from the interaction with anticoagulants, not from toxicity. An upper limit for vitamin K has never been derived, for lack of data, and in the studies cited by the BfR 180 µg of MK-7 over three years produced no observed adverse effects in healthy adults. Anyone taking anticoagulants clears the intake with their doctor.
Do I get enough K2 from food? Total vitamin K2 sits at around 30 to 38 µg per day in the German surveys, mostly from cheese and other fermented foods. MK-7 in particular, by contrast, barely occurs — in the EPIC cohort Heidelberg the median was 0.8 µg per day. Anyone wanting to take in MK-7 through the diet ends up practically at natto.
Sources: Regulation (EU) No 432/2012 (list of authorised health claims, official wording); Regulation (EC) No 1924/2006, Annex (15 % of the nutrient reference value per daily portion as a condition); Regulation (EU) No 1169/2011, Annex XIII (nutrient reference values: vitamin K 75 µg, calcium 800 mg, vitamin D 5 µg); EFSA NDA Panel, "Scientific Opinion on the substantiation of a health claim related to vitamin K2 and contribution to the normal function of the heart and blood vessels (ID 125, further assessment)", EFSA Journal 2012;10(6):2714 (no cause-and-effect relationship established; missing intervention studies, contradictory cross-sectional and cohort data, weak mechanistic evidence); Bundesinstitut für Risikobewertung, "Höchstmengenvorschläge für Vitamin K in Lebensmitteln inklusive Nahrungsergänzungsmitteln" (80 µg K1 or 25 µg K2 per recommended daily portion, no UL derived, warning for people on anticoagulants, INR thresholds 150 µg K1 after Schurgers et al. 2004 and 45 µg K2 after Theuwissen et al. 2013); BfR opinion No 065/2023 of 7 December 2023, "Hochdosierte Nahrungsergänzungsmittel mit Vitamin D können langfristig die Gesundheit beeinträchtigen" (benefit of the combination with vitamin K not established; vitamin-K-dependent proteins osteocalcin and matrix Gla protein; half-lives of MK-7 compared with K1; MK-7 below 10 µg/day under coumarin therapy; intake data from the EPIC cohort Heidelberg after Nimptsch et al. 2008 and the Bavarian Food Consumption Survey II after Nimptsch et al. 2009; safety data after Marles et al. 2017); BfR opinion No 009/2021 (maximum-amount proposal for calcium, 500 mg per recommended daily portion); Scientific Committee on Food (2003), confirmed by EFSA in 2012 (UL calcium 2,500 mg/day); EFSA NDA Panel (2017), Dietary Reference Values for vitamin K; D-A-CH reference values (2015), estimated values for vitamin K; Deutsche Gesellschaft für Ernährung, reference values for calcium (1,000 mg for adults); composition and recommended intake according to the label of the products named.
