Most Vitamin K2 products do not specify which form of K2 they contain. When they do, the explanation of why it matters is usually missing.
It matters because of a very simple pharmacokinetic fact: MK-4 and MK-7 have half-lives that differ by a factor of roughly 36. For once-daily supplementation — which is how virtually everyone takes supplements — this is the difference between a dose that covers you and one that largely does not.
MK-4 and MK-7: The Same Mechanism, Very Different Duration
Both forms are menaquinones — members of the Vitamin K2 family. Both activate osteocalcin (which binds calcium into bone) and Matrix GLA Protein (which prevents calcium from depositing in artery walls). The activation mechanism is the same.
What differs is pharmacokinetics: how long each form remains active in circulation after a dose.
- A landmark study published in Blood (Schurgers et al., 2007) measured circulation time of both forms in healthy volunteers following a single dose.
- MK-4 was cleared from blood within 4–8 hours. Calculated half-life: approximately 1–2 hours.
- MK-7 remained detectable in blood for up to 72 hours. Calculated half-life: approximately 72 hours.
What This Means for Once-Daily Dosing
A single daily dose of MK-7 maintains consistent K2-dependent protein activation throughout the 24-hour period — including overnight, and into the following day.
A single daily dose of MK-4 provides measurable coverage for a few hours, then clears. For the remaining 20+ hours, tissue K2 levels from that dose are negligible.
Matrix GLA Protein in particular requires sustained K2 levels to remain active. MGP is produced continuously in vascular tissue, and each new MGP protein requires K2 carboxylation to activate its arterial-protective function. Rapid MK-4 clearance leaves extended periods where new MGP proteins cannot be activated — which is precisely the protective gap you would want to avoid.
The Research That Uses MK-7
The cardiovascular associations from the Rotterdam Study were observed in populations with higher K2 intake from natto — an MK-7-rich food. The 2013 Knapen et al. trial in Thrombosis and Haemostasis that showed improved vascular stiffness after three years used 180mcg MK-7 per day. The evidence base for K2’s cardiovascular benefit is built predominantly on MK-7.
There are trials showing benefit from MK-4 — specifically Japanese studies at 45mg three times daily for osteoporosis. But 45mg three times daily is a pharmaceutical protocol. It has nothing to do with a 100–200mcg once-daily supplement. The evidence does not transfer.
Why MK-4 Still Appears in Products
It is cheaper to produce synthetically. High milligram counts look appealing on packaging. And most consumers do not know to ask about half-life.
Frequently Asked Questions
Is there any reason to prefer MK-4?
At the pharmacological doses used in Japanese osteoporosis trials — 45mg three times daily — MK-4 shows independent bone-related effects. For once-daily supplementation at typical doses, MK-7’s pharmacokinetic advantage makes it the better choice.
What dose of MK-7 is appropriate?
Clinical research has used 45–360mcg per day. A daily dose of 55–180mcg is a reasonable evidence-based range for healthy adults. There is no ICMR RDA for K2 specifically.
Is all MK-7 the same quality?
No. Fermentation-derived MK-7 varies in purity and isomer profile. Trans-MK-7 is the biologically active form; cis-isomers are inactive. Branded, documented MK-7 ingredients provide traceability and confirmed isomer profile that generic K2 does not.
Can I take too much MK-7?
At supplemental doses up to 360mcg per day, no toxicity has been reported. The main caution is for people on warfarin — K2 affects anticoagulation pathways and warfarin dosing may need adjustment.
If MK-7 stays in circulation for 72 hours, could I take it every other day?
Theoretically, blood levels would remain meaningful. In practice, daily supplementation is the design validated by clinical research. Consistency is also easier to maintain as a habit than alternate-day dosing.