Supplement quality stories usually concern how much of an ingredient a product contains. MK-7 adds a subtler failure mode: a product can contain exactly the labelled milligrams of menaquinone-7 and still deliver a fraction of the biology — because MK-7 exists as geometric isomers, and only one of them works. This is the quality question most labels never mention, and the reason isomer testing has become the differentiator among serious K2 products.
Same formula, different shape, different biology
MK-7’s side chain is built from seven isoprene units linked by double bonds, and each double bond can adopt one of two geometries: trans (extended, straight) or cis (kinked). Natural MK-7 — as bacteria have always made it — is all-trans: every bond extended, the molecule straight as a ruler. That geometry is not cosmetic. Vitamin K function depends on the side chain seating into the hydrophobic channels of gamma-glutamyl carboxylase’s membrane environment and into lipoprotein transport; a cis kink bends the molecule out of fit. The analytical and biological literature (Szterk 2018, and the surrounding analytical-chemistry work) is unambiguous: cis-MK-7 shows essentially no vitamin K activity — it is a passenger with the passport of an active molecule.
Where cis contamination comes from
The isomer problem is a manufacturing-route problem. Chemical synthesis of MK-7 builds the side chain through reactions that, without tight stereochemical control, produce a mixture of geometries; poorly controlled processes have been documented delivering products with substantial cis fractions — historically, market surveys have found synthetic-route products ranging anywhere from excellent to majority-inactive. Fermentation-derived MK-7 — produced by Bacillus subtilis and related strains, the natto route — is naturally all-trans, because bacterial enzymes are stereospecific by construction; the isomer purity is inherited from the biology rather than imposed by process control. (Careful storage still matters: prolonged UV exposure can isomerise even good material — one more argument in the packaging-and-format chain.)
Why a basic potency assay cannot catch it
Here is the uncomfortable analytical truth: a standard content assay — even standard HPLC with typical reversed-phase columns — quantifies “MK-7” by mass and can report cis and trans together as one number. A product that is 60% inactive isomer passes a naïve potency test at full label claim. Separating the isomers requires isomer-resolving chromatography: specialised stationary phases (C30 columns are the classic choice) or optimised methods that split the cis and trans peaks, quantifying each — the methodology Szterk and colleagues applied when surveying commercial supplements (Food Chem, 2018) and finding exactly the variability the mechanism predicts. This test exists, is routine in competent laboratories, and is rarely published by brands — largely because it can only be flattering to products that have nothing to hide.
Reading a certificate of analysis like an isomer sceptic
Applying the CoA-reading method to K2 specifically, the questions become: Does the certificate state “all-trans MK-7” as the analyte — with a declared all-trans percentage (≥96–98% is the serious-product range) — or merely “menaquinone-7”? Does the method column reference an isomer-resolving HPLC procedure, not just “HPLC”? Is the source declared (fermentation-derived being the naturally all-trans route)? A certificate answering all three has measured the thing that matters; a certificate silent on isomers has measured milligrams of molecule-shaped material. On K2 labels, “all-trans” is not decoration — it is the entire difference between the trial-tested vitamin and its inert twin.
The clinical bottom line
MK-7’s biology belongs exclusively to the all-trans isomer; cis-MK-7 is inactive cargo that ordinary potency testing counts as product. Fermentation makes all-trans by nature, sloppy synthesis makes mixtures, and only isomer-resolving HPLC can tell — so the quality signal to demand is explicit: all-trans MK-7, percentage stated, isomer-specific method on the certificate. Everything else is label-claim theatre.
Primary sources
- Szterk A, Zmysłowski A, Bus K. Identification of cis/trans isomers of menaquinone-7 in food as exemplified by dietary supplements. Food Chem. 2018;243:403–409. doi:10.1016/j.foodchem.2017.09.121
- Berenjian A, Mahanama R, Talbot A, et al. Efficient media for high menaquinone-7 production: response surface methodology approach. N Biotechnol. 2011;28(6):665–672. doi:10.1016/j.nbt.2011.07.007 (fermentation route)
- Schurgers LJ, Vermeer C. Determination of phylloquinone and menaquinones in food: effect of food matrix on circulating vitamin K concentrations. Haemostasis. 2000;30(6):298–307. doi:10.1159/000054147
- Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutr J. 2012;11:93. doi:10.1186/1475-2891-11-93
- ISO/IEC 17025:2017 — competence requirements the isomer-testing laboratory itself should meet. iso.org
Educational information on analytical quality, not medical advice. Anticoagulated readers: the interaction rules apply to all active vitamin K, isomer-pure or otherwise.
Was this article helpful?
Related Coverage
Editorial standards. This article was produced under the GMJ News editorial process, with oversight by the GMJ Editorial Board. Our editorial process. Spotted an error? Contact the editorial team.
