Vitamin K2 quality: label, stability, origin

The amount on the tub is not a measurement but a promise: it has to hold until the end of the shelf life, and the law grants a wide corridor for that. Whether what is stated on the front is really inside is decided in three places, none of them on the display side of the pack — at the declaration, at the stability (what lies next to the K2 in the same tablet and how it is stored) and at the origin of the raw material. Analyses of market stock find the outliers exactly there: anything from 55 to 116 per cent of the declared content turned up.

This article shows what has to appear on a K2 label, what may be missing, and which two or three statements make the difference in practice.

What must be on the label — and what may be missing

For food supplements, Article 8 of Directive 2002/46/EC (in Germany transposed by § 4 of the Nahrungsergänzungsmittelverordnung) sets out which particulars are mandatory: the amount of the nutrients per recommended daily portion and the share of the nutrient reference value (NRV) in per cent. For vitamin K that reference value is 75 µg per day (Regulation (EU) No 1169/2011, Annex XIII), so 200 µg of MK-7 appears there as around 267 %. Which compound supplies the vitamin is not stated in the nutrition table but in the list of ingredients — for vitamin K2, the only authorised entry is “menaquinone” (Directive 2002/46/EC, Annex II).

Particular	Mandatory?	What it says about quality
Amount per daily portion in µg	yes	the reference figure for everything else
% of the nutrient reference value	yes	merely a conversion, not a quality measure
Recommended intake	yes	without it the µg figure cannot be placed
Ingredient “menaquinone”	yes	the legally authorised source
Best-before date, batch number	yes	the precondition for any traceability
Form (MK-7 or MK-4)	no	only here does the figure become concrete
Isomerism (all-trans, purity)	no	the line that actually carries information
Production route (“from natto fermentation”)	no	a pointer to the raw material
Carrier oil, capsule shell, additives	yes (ingredients)	decides tolerability and stability

The lower half of the table is the interesting one: everything that actually says something about the contents is voluntary. A label reading “vitamin K2 200 µg” and nothing else is entirely compliant — and leaves open which chain length, which geometry and which production route lie behind it. What those terms mean is set out in Vitamin K2 forms; why the geometry decides which part is active, in Vitamin K2 MK-7 all-trans.

The tolerance range: 200 µg is 160 to 300 µg

Hardly anyone expects it, but the declared figure is an average with an officially conceded spread. The European Commission’s guidance on tolerances for nutrition labelling (December 2012) gives in Table 2, for food supplements:

Nutrient group	lower tolerance	upper tolerance
Vitamins	−20 %	+50 %
Minerals	−20 %	+45 %

Measurement uncertainty is already included in those figures. For 200 µg of declared vitamin K2 this means: 160 to 300 µg would not be objected to in an official control. And the guidance states expressly in section 2.2 that the measured values should lie within this range throughout the shelf life — not only on the day of filling. That is exactly why many manufacturers weigh in more than the pack states from the outset.

This corridor is the reason why “quality” with K2 is not a matter of good intentions: whoever does not know the loss cannot factor it in.

Stability: what lies next to the K2 in the tablet

MK-7 is more heat-stable than its reputation suggests — it breaks down above all under UV light and in an alkaline environment. That makes the composition of the tablet a quality question, and in a way most buyers have the wrong way round.

A study by Orlando and colleagues (Molecules 2019;24(5):829) stored three MK-7 raw materials — two obtained by fermentation, one synthetic — together with typical accompanying substances and followed them for twelve months at 25 °C/60 % relative humidity as well as six months under stress conditions at 40 °C/75 %:

Admixed substance	Result
Calcium citrate	unremarkable, no loss of stability with the pure raw material
Calcium carbonate	unremarkable
L-arginine	clear degradation under stress conditions
Magnesium oxide	strongest degradation; under stress conditions the content fell far below 90 %

So the widespread rule of thumb “calcium destroys the K2” misses the point. What was measured as the disruptive factor was the alkaline magnesium oxide, and the authors trace the effect precisely to that: to the alkalinity of the formulation. In practice this does not mean magnesium and K2 cannot be taken on the same day — they are then not lying in the same pressed tablet for months. It means that a multimineral combination product with magnesium oxide and K2 in one tablet is the riskiest design. Which combinations can sensibly be separated at intake is covered in How to take vitamin K2; how calcium and K2 are connected, in Vitamin K2 and calcium.

The raw material beats any mineral

Even more clearly than the accompanying substance, the purity of the raw material took effect in the same study. The high-purity material (99.3 % all-trans MK-7, no unidentified side peaks) stayed stable over twelve months. The two impure samples — 19 and 23 unknown peaks in the chromatogram respectively — decayed rapidly: the synthetic material had lost half of its MK-7 within one month under entirely normal storage conditions. The accompanying market comparison found contents between 55 and 116 % of the declaration, and the deviation went hand in hand with the impurity profile.

Packaging cannot make up for that — it can only avoid making it worse. Amber glass, opaque blisters or a closed tub protect against UV; stored dry and at room temperature, not on the windowsill, and the rest is done.

Oil or tablet

A Polish research group analysed eight MK-7 preparations, four hard tablets and four soft capsules with oil (Szterk et al., Molecules 2018;23(5):1056). The tablets contained 22.7 to 87.7 µg per unit and thus frequently lay below the claim; the oil capsules came to 26 to 373.8 µg and thus lay partly far above it — the authors put this down to loss during storage being factored in. At the same time they found considerable amounts of inactive isomers: 70.9 to 218.7 µg of cis/trans MK-7 and 5.5 to 16.9 µg of cis/trans MK-6 per unit.

No recommendation for one dosage form follows from this, only the sober finding that both designs have their typical deviation. What the form means for uptake is described in How to take vitamin K2.

Origin: where the raw material comes from and who tested it

Vitamin K2 is produced either by fermentation with Bacillus subtilis natto — that is how the EU authorisation puts it — or by chemical synthesis. Enzymes work stereospecifically and deliver all-trans from the start; synthesis initially produces a mixture of isomers that has to be separated off. This is precisely why the Polish group was able to infer the actual origin from high cis fractions: genuine natto contains all-trans MK-7 only, so a preparation with a high cis fraction can hardly come from pure fermentation, whatever the pack claims.

How origin and testing can be traced:

• A named branded raw material. If the trade name of the K2 raw material is on the label, there is a public specification to read it against. If it is missing, only the manufacturer’s word remains.
• An isomer statement with a figure. “≥ 99 % all-trans” is a test value, “all-trans” alone is an assertion. Only separate determination by isomer shows what is active — a summed “total vitamin K2” analysis does not.
• Batch and best-before date on the pack. Without a batch number there is no traceability, and the date is the period for which the declared content holds.
• A certificate of analysis on request. Reputable suppliers issue one for the specific batch; content, isomer distribution and heavy metals are the interesting parts.
• Contaminants. Regulation (EU) 2023/915 sets maximum levels for food supplements of 3.0 mg/kg lead, 1.0 mg/kg cadmium and 0.1 mg/kg mercury. Those are limits, not quality seals — but a test report that states them shows that measurement took place at all.

In our own range the form is therefore in the product name and not in the small print — for instance with Vitamin D3 20,000 IU + K2 MK-7 all-trans or, at a daily dose, with Vitamin D3 4,000 IU + K2 200 µg MK-7. The overview of the strengths is in the vitamin K2 category.

The check in thirty seconds

Step	What to look at
1. Daily portion	How many capsules make up the stated µg?
2. Form	Does it say MK-7 — or only vitamin K2?
3. Isomerism	All-trans, better still with a percentage
4. Ingredients	Magnesium oxide and K2 in the same tablet?
5. Packaging	opaque, tightly closed
6. Date and batch	present and legible

None of this requires expert knowledge, and none of the six lines costs money — they only cost a glance at the back. How a price comparison per microgram follows from it is set out in Buying vitamin D3 + K2.

What may be said about vitamin K

The authorised health claims are set out in Regulation (EU) No 432/2012. They apply to the nutrient vitamin K, not to a particular form, purity or brand:

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

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

Frequently asked questions

Is a more expensive K2 preparation automatically the better one? No. Price says nothing about isomer distribution, and at 200 µg per daily portion the raw material cost is small anyway compared with packaging and distribution. What carries information is the statements on the back, not the figure on the price tag.

Should I buy magnesium and vitamin K2 separately? Buy yes, take not necessarily. What is problematic according to the study cited is the permanent storage of magnesium oxide and MK-7 in the same tablet, not taking them on the same day. Two separate preparations solve the problem with no effort at all.

How do I tell that my preparation has suffered? Not from the outside at all — MK-7 breaks down without smell or colour. That is why packaging, storage place and best-before date are the only levers you hold yourself. Opened tubs belong closed in the cupboard, not on the windowsill or on the shelf above the cooker.

Is “from natto” a quality seal? It describes the production route, not the result. The route speaks for all-trans material being present, but that is only substantiated by the isomer statement. Conversely, cleanly purified synthetic MK-7 can reach the same purity — the difference then lies in the accompanying substances, as described in Vitamin K2 forms.

Sources: Directive 2002/46/EC, Article 8 and Annex II (authorised vitamin K sources); Regulation (EU) No 1169/2011, Annex XIII (nutrient reference value for vitamin K, 75 µg); European Commission, DG Health and Consumers, “Guidance document for competent authorities for the control of compliance with EU legislation … with regard to the setting of tolerances for nutrient values declared on a label”, December 2012, Table 2 and section 2.2; Regulation (EU) 2023/915 on maximum levels for certain contaminants in food; Regulation (EU) No 432/2012; Orlando P, Silvestri S, Marcheggiani F et al., “Menaquinone 7 Stability of Formulations and Its Relationship with Purity Profile”, Molecules 2019;24(5):829 (PubMed 30813554); Szterk A, Bus K, Zmysłowski A, Ofiara K, “Analysis of Menaquinone-7 Content and Impurities in Oil and Non-Oil Dietary Supplements”, Molecules 2018;23(5):1056 (PubMed 29724016).