Vitamin K2 interactions: medicines and nutrients

With vitamin K2 there is one interaction that is documented in numbers and clinically relevant: the one with coumarin-type anticoagulants. Next to it stands a second, less well known group — medicines that disturb fat absorption in the gut and carry fat-soluble K2 out with it. And there is a third group: combinations that keep appearing online as interactions and turn out not to be any on closer inspection. This article sorts the three apart and names the source for every statement.

The one that really counts: coumarins

Four clotting factors only become functional in the liver with the help of vitamin K. The vitamin is consumed in the process and then recycled — and it is exactly this recycling that coumarin-type anticoagulants block: phenprocoumon (Marcumar, Falithrom), warfarin and acenocoumarol. Anyone who supplies vitamin K from outside refills the pool directly and partly bypasses the block; the INR falls, the therapy works more weakly than it was set to. Conversely, whoever suddenly stops a K2 product after weeks of use sees the INR rise.

How little it takes was measured by two studies in twelve healthy volunteers each, who were set to an INR of 2.0 with acenocoumarol and then supplied with increasing amounts of vitamin K:

Amount supplied per day	Observation
150 µg vitamin K1	threshold for a statistically detectable drop in INR
45 µg vitamin K2 (MK-7)	the same threshold, at one third of the amount

From the comparison of the two thresholds the German Federal Institute for Risk Assessment (BfR) concludes that vitamin K2 counteracts coumarin therapy about 3.5 times as strongly as vitamin K1. With an uncertainty factor of about 2, the BfR derives from this its proposed maximum levels for food supplements: 80 µg vitamin K1 and 25 µg vitamin K2 per recommended daily portion, plus a note that people on anticoagulant medication should seek medical advice before consumption. Both are a proposal and not applicable law — there is no statutory maximum level for vitamin K in Germany, and a Tolerable Upper Intake Level for vitamin K could never be derived for lack of data.

Commercially available K2 products sit clearly above this proposal at 100 to 200 µg MK-7. That is not a peculiarity of individual brands but the normal case in this product group — including our Vitamin D3 4,000 IU + K2 200 µg MK-7, which contains 200 µg MK-7 per tablet.

Why spacing out the doses does not help here

With minerals that compete for the same transport routes in the gut, a gap of a few hours helps. MK-7, by contrast, has a half-life of around 68 hours and accumulates in serum with daily intake — there is no time of day at which it is not present. The difference between the chain lengths is described in Vitamin K2 forms; the complete list of drug classes including DOACs and aspirin is in Vitamin D3 + K2 and blood thinners.

Something different applies to food than to supplements: the EU Scientific Committee on Food advises those affected to keep their vitamin K intake from food constant — not to minimise it. Fluctuation is the problem, not the amount as such. Which foods contribute how much is set out in Vitamin K2 in food.

Medicines that slow absorption

Vitamin K2 is fat-soluble and needs dietary fat and bile acids in order to be absorbed. Anything that disturbs this route also lowers the amount that actually arrives — regardless of what the label says:

Substance / group	What happens	Practical consequence
Orlistat (lipase inhibitor)	part of the dietary fat is not split and not absorbed; with it the fat-soluble vitamins A, D, E and K	the summary of product characteristics recommends a multivitamin at bedtime — that is, at a distance from the meal
Colestyramine, colestipol (bile acid sequestrants)	bind bile acids in the gut that are needed for fat absorption	with long-term use, vitamin K status is monitored via clotting values
Liquid paraffin (lubricant laxative)	fat-soluble vitamins pass into the non-absorbable oil	at least one hour away from the meal; long-term use is not intended anyway

With orlistat both effects come together: the product information for the approved preparations notes that absorption of the fat-soluble vitamins may be impaired — and that with concomitant warfarin or other anticoagulants, decreased prothrombin values and increased INR values have been reported, which is why the INR should be monitored. A vitamin K2 product therefore shifts two adjusting screws at once in this constellation.

With the bile acid sequestrants, spacing really is a lever, because they bind in the gut and do not intervene in liver metabolism. How to place K2 with a meal so that there is enough fat present at all is set out in How to take vitamin K2.

Antibiotics: what is true and what is not

“Antibiotics kill the gut bacteria that produce vitamin K2” — this sentence appears in many guides and mixes up two things that ought to be kept apart.

First, the gut flora. Bacteria in the large intestine do indeed form menaquinones. Whether and how much of that is absorbed is open: in its derivation of the dietary reference values for vitamin K (2017), the EFSA states that absorption of bacterially formed menaquinones from the distal gut is uncertain and their contribution to vitamin K status unclear. For the same reason the EFSA based its reference value on phylloquinone (K1) alone — for adults 1 µg per kilogram of body weight and day, so 70 µg for a person weighing 70 kg. In depletion experiments the bacterial production could not compensate a dietary shortfall of K1, and that was true of participants not on antibiotics either. So whoever regards the gut flora as a silent reserve overestimates it — which also means: a course of antibiotics does not remove a large reserve.

Second, individual substances. Some cephalosporins with an NMTT side chain — cefamandole, cefotetan, cefoperazone or latamoxef, for instance — inhibit vitamin K epoxide reductase in the liver directly, that is, the same enzyme as the coumarins. That is not a side effect via the gut flora but a direct intervention in the vitamin K cycle; it was demonstrated by the brief appearance of K1 epoxide in the blood after vitamin K administration, which did not occur with cephalosporins lacking this side chain. Those affected were typically severely ill, artificially fed hospital patients — not someone taking an oral antibiotic at home for a week.

In practice this means: an ordinary course of antibiotics is in itself no reason to supplement vitamin K2, and no reason to stop it either.

Nutrients and combination products

Here the evidence is thinner, and the widespread rules of thumb often miss the point:

Combination	What is documented	Practical consequence
Vitamin E, high dose	1,000 IU α-tocopherol daily over twelve weeks raised PIVKA-II in one study, a marker for poor vitamin K status	the EFSA sets the Upper Intake Level for vitamin E at 300 mg per day — precisely because of the effect on blood clotting
Vitamin D3	no interaction with clotting; the two are combined for other reasons	combination products are unproblematic
Calcium	no documented disturbance of K2 absorption	spacing is not necessary
Magnesium oxide in the same tablet	alkaline formulations degrade MK-7 during storage	not an intake problem but a shelf-life problem

The last point is regularly misunderstood. The degradation was measured in preparations that lay together in the same pressed tablet for months — not in the gut of someone taking both on the same day. The study behind it and what it means for choosing a product is set out in Vitamin K2 quality; on the relationship between K2 and calcium there is Vitamin K2 and calcium.

The vitamin E line is remarkable: the EFSA derived the Upper Intake Level for vitamin E from the effect on blood clotting of all things — from a NOAEL of 800 IU per day with an uncertainty factor of 2. And it states explicitly that this value does not apply to people taking anticoagulant or antiplatelet medication. So anyone already in that calculation should not consider high-dose vitamin E and high-dose K2 independently of one another.

Who is better off asking first

• On phenprocoumon, warfarin or acenocoumarol: neither start a K2 product on your own initiative nor stop it abruptly — both shift the INR, only in opposite directions.
• Before a planned operation or dental procedure: vitamin K2 belongs on the list of things you mention, because it concerns the same adjusting screw as the anticoagulation.
• With a known fat malabsorption disorder or long-term use of the substances named above: the amount that arrives is not the amount on the label.
• If you need vitamin D but do not want vitamin K: in a combination tablet the two cannot be separated. A plain D3 product such as Vitamin D3 4,000 IU solves that without arithmetic; the combinations are in the vitamin K2 category.

How much K2 is customary at all and how that relates to the reference value of 75 µg is set out in Vitamin K2 daily requirement.

What may be said about vitamin K

The authorised health claims are laid down in Regulation (EU) No 432/2012:

• Vitamin K contributes to normal blood clotting.
• Vitamin K contributes to the maintenance of normal bones.

The first claim describes the situation precisely: vitamin K belongs to normal clotting. Anyone deliberately keeping that clotting damped down with medication therefore has a different interest in this vitamin than everyone else.

Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle.

Frequently asked questions

I take a DOAC — do I have to do without K2? Apixaban, edoxaban, rivaroxaban and dabigatran act directly on clotting factors and do not need the vitamin K cycle for that; there is neither an adjusted INR here nor the counteraction described above. The BfR warning is nevertheless worded generally for “anticoagulant medication” — a brief question at the practice costs nothing.

Do I have to leave a gap between K2 and my other tablets? Only with the substances that bind in the gut or disturb fat absorption — bile acid sequestrants, paraffin, orlistat. With everything that acts in liver metabolism, spacing achieves nothing, because MK-7 stays in the blood for days.

I had a course of antibiotics — should I top up K2? There is no sound basis for that. According to the EFSA assessment the contribution of gut bacteria to vitamin K status is unclear and in experiments too small to compensate a dietary shortfall — so it is also not a reserve that an antibiotic could clear out.

Can I take K2 and a high-dose vitamin E product together? Both concern the same point in metabolism, though in opposite directions: high-dose vitamin E acted in the cited study more like a weak vitamin K antagonist. As long as vitamin E stays within the range of customary products this is not an issue; at 800 IU and above the combination is worth discussing — all the more so under anticoagulants.

Sources: BfR, “Proposed maximum levels for vitamin K in foods including food supplements” (sections 2.1 to 2.4, referring to SCF 2003); Schurgers LJ et al., Blood 104(9), 2004 (PubMed 15231565); Theuwissen E et al., J Thromb Haemost 11(6), 2013 (PubMed 23530987); EFSA NDA Panel, “Dietary reference values for vitamin K”, EFSA Journal 2017;15(5):4780; EFSA NDA Panel, “Scientific opinion on the tolerable upper intake level for vitamin E”, EFSA Journal 2024;22(8):8953; Booth SL et al., “Effect of vitamin E supplementation on vitamin K status in adults with normal coagulation status”, Am J Clin Nutr 2004;80(1):143–148 (PubMed 15213041); Shearer MJ et al., “Mechanism of cephalosporin-induced hypoprothrombinemia”, J Clin Pharmacol 1988;28(1):88–95 (PubMed 3350995); summaries of product characteristics for orlistat (120 mg hard capsules), colestyramine and liquid paraffin; Orlando P et al., Molecules 2019;24(5):829 (PubMed 30813554); Regulation (EU) No 1169/2011, Annex XIII; Regulation (EU) No 432/2012.