Start with what may be said, because it is short
Health claims about food in the European Union are governed by Regulation (EC) No 1924/2006. A claim may only be made if it appears on the EU Register of nutrition and health claims, and only in the wording that was authorised. A shop’s own journal is a commercial communication, so this page is bound by exactly the same rule as the label on the bottle.
For these two vitamins, this is the complete authorised set:
- Vitamin D contributes to the normal absorption and utilisation of calcium and phosphorus.
- Vitamin D contributes to normal blood calcium levels.
- Vitamin D contributes to the maintenance of normal bones.
- Vitamin D contributes to the maintenance of normal muscle function.
- Vitamin D contributes to the maintenance of normal teeth.
- Vitamin D contributes to the normal function of the immune system.
- Vitamin D has a role in the process of cell division.
- Vitamin K contributes to normal blood clotting.
- Vitamin K contributes to the maintenance of normal bones.
Everything below is mechanism — how the molecules behave — which is chemistry rather than a claim about what a product will do for you. It also happens to be the more interesting half.
Vitamin D arrives switched off
Cholecalciferol, the D3 on a label, does nothing as it arrives. It is converted twice: in the liver to 25-hydroxyvitamin D, the form a blood test measures, and in the kidney to 1,25-dihydroxyvitamin D, the active form. That second step is regulated by the body rather than by how much you swallowed — a structural fact worth knowing about the whole category.
The active form acts on the intestine, where it governs how much dietary calcium is absorbed rather than passed through. That is the mechanism sitting under the authorised sentence about the normal absorption and utilisation of calcium and phosphorus.
One label note while we are here. D3 and D2 are different molecules: D3 is cholecalciferol, D2 is ergocalciferol. EU labelling requires the source to be named, so the pack tells you which you have. Ours says cholecalciferol.
Vitamin K is a cofactor, and cofactors are specific
Vitamin K does one chemical job. It is the cofactor for an enzyme, gamma-glutamyl carboxylase, which adds a carboxyl group to particular glutamate residues in certain proteins. The modified residue is called a Gla residue, and the proteins carrying them are called vitamin-K-dependent proteins.
Without that modification the proteins are still made, but unfinished. Carboxylation is the step that puts them into the form that binds calcium.
Two of these proteins are well known by name, and both map onto an authorised claim. Prothrombin is a clotting factor, which is why the authorised statement for vitamin K concerns normal blood clotting. Osteocalcin is made in bone, which is why the second authorised statement concerns the maintenance of normal bones.
Why the two travel in one bottle
Put the mechanisms side by side. Vitamin D governs how much calcium is absorbed. Vitamin K activates the proteins that bind it. One acts on the quantity entering the system; the other finishes the proteins that handle it.
That is the argument for a combined product, and it is an argument about chemistry rather than about outcomes. We are not going to tell you what the combination will do for you, because nobody is authorised to say that. What we can tell you is why a formulator reaches for both rather than one.
There is also a plain manufacturing reason, which is rarely mentioned and is half the answer. Both vitamins are fat-soluble, both need an oil to disperse in, and both are dosed in micrograms. One carrier serves both. A combined tablet has to solve two solubility problems inside a compressed solid; a combined oil solves one, once.
MK-4 and MK-7
“Vitamin K2” is not one substance. It is a family of menaquinones differing in the length of a side chain, and the number after MK is the number of isoprene units in that chain. MK-4 has four. MK-7 has seven.
Three differences are worth knowing when you read a label:
- Origin. MK-7 is typically produced by bacterial fermentation. MK-4 is typically produced by synthesis. This is why one is often described as fermented and the other is not.
- Scale of the dose. The two are dosed on different scales entirely: MK-4 in milligrams, MK-7 in micrograms. Two packs both saying “vitamin K2” can differ in quantity by a factor of a hundred and neither is mislabelled.
- The same reference value. Both count against one NRV for vitamin K, 75 µg, listed in Annex XIII of Regulation (EU) No 1169/2011. So the percentage on the pack does not distinguish them either.
Which means a K2 figure is not comparable between two products until you know which menaquinone it is. A label saying only “vitamin K2” has not told you.
What “all-trans” is declaring
The MK-7 side chain contains double bonds, and each double bond can sit in one of two geometries: cis or trans. The all-trans form — every double bond in the trans configuration — is the one produced by fermentation and the one raw-material specifications are written against. Cis isomers arise as a by-product of synthesis and are handled as an impurity of the material.
So “all-trans MK-7” on a label is not ornament. It is a statement about the isomeric purity of the raw material, and it is the sort of thing a supplier can either document or cannot. A label saying only “MK-7”, or only “vitamin K2”, has declined to say.
What is on our label
One drop carries 25 µg of vitamin D3 as cholecalciferol — 1,000 IU, 500% of the NRV — and 20 µg of vitamin K2 as all-trans menaquinone-7, 27% of the NRV. The whole ingredient list is three lines: medium-chain triglycerides from coconut oil 96.5%, cholecalciferol 2.5%, menaquinone-7 1%. The oil is there because the two vitamins need a carrier, which is the same reason they share a bottle.
500% is a large-looking number, and we print it rather than bury it. The reference value for vitamin D is 5 µg; five times five is twenty-five. For context, the tolerable upper intake level EFSA sets for adults is 100 µg a day. If you already take another vitamin D product, or you are not sure how this fits with anything else you take, ask your doctor or pharmacist before you start. Do not exceed the stated daily dose.
Where this article stops
Deliberately, here. We have described what the molecules do chemically and why that leads a formulator to put them in one bottle. We have quoted the only sentences the EU Register authorises anyone to say about their effects, and we have not walked past them into anything larger.
A food supplement is not a substitute for a varied and balanced diet or for a healthy lifestyle, and it is not a medicine. If you have a diagnosed condition, take prescribed medicines — anticoagulants in particular, where vitamin K is directly relevant — are pregnant or breastfeeding, or are buying for a child, speak to a doctor or pharmacist first.