Supplement analysis backed by scientific evidence · PT

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Vitamin K2 (MK-4)

MK-4 is a licensed osteoporosis drug in Japan at 45 mg/day — but that is pharmacology, not supplementation. At the microgram-to-milligram doses sold as supplements, MK-4 barely registers in the bloodstream, and its very short half-life makes MK-7 the more practical form.

What the science says

  • Reduces fractures at pharmacological doses Limited evidence

    A 2006 meta-analysis of vitamin K trials — nearly all Japanese studies of MK-4 at 45 mg/day — reported striking reductions in vertebral (odds ratio 0.40), hip (OR 0.23) and all non-vertebral fractures (OR 0.19). Those numbers are almost certainly too good: the constituent trials were small, unblinded or poorly blinded, and the effect has not been reproduced in larger, better-controlled Western trials. Treat it as a hypothesis from one country's literature, not an established effect.

  • Supplement doses raise vitamin K2 status Limited evidence

    Mostly they do not. In a bioavailability study in healthy women, a single 420 µg dose of MK-4 produced no detectable increase in serum MK-4, while the same dose of MK-7 raised serum MK-7 substantially. MK-4's circulating half-life is a matter of hours versus roughly three days for MK-7. A 100 µg or 1 mg MK-4 capsule taken once daily is unlikely to change your measurable K2 status at all.

  • Directs calcium into bone and away from arteries Limited evidence

    The mechanism — gamma-carboxylation of osteocalcin and matrix Gla protein — is real biochemistry. The clinical claim is not supported for MK-4: no randomised trial of MK-4 has shown reduced arterial or valvular calcification, and the trials that did test this hypothesis used MK-7 and were largely negative.

  • MK-4 is superior to MK-7 because it is 'the human form' Limited evidence

    MK-4 is indeed the menaquinone tissues make from K1 and other menaquinones, and it is the form found in some tissues. But that argument works against oral MK-4, not for it: your body already converts, and the oral molecule barely reaches circulation. If you want to change vitamin K status with a supplement, MK-7 is the form with the pharmacokinetics to do it.

Dosage & safety

Studied doseThe Japanese prescription regimen is 45 mg/day (15 mg three times daily) taken with food — a dose roughly 500x what supplement capsules contain. Supplements supply 100 µg to 5 mg/day. Adequate intake for vitamin K overall is 90–120 µg/day and is met by leafy greens as K1. MK-4 requires dietary fat and frequent dosing to achieve anything; a once-daily microgram dose is largely inert.
SafetyNo toxicity is known even at 45 mg/day, and vitamin K has no established upper limit. The one serious interaction is decisive: any vitamin K supplement antagonises warfarin, acenocoumarol and other vitamin K antagonists and can destabilise INR — do not start or stop one without your prescriber, and if you take a VKA, consistency of intake matters more than avoidance. No interaction with DOACs (apixaban, rivaroxaban). Most supplemental MK-4 is synthetic, typically derived from geranylgeraniol; 'natural' MK-4 in meaningful quantity is rare in food. Pharmacological 45 mg dosing has not been established as safe in pregnancy or lactation. Not banned in sport.

Scientific references

Where to buy

Nutricost, Vitamin K2 MK-4, 100 mcg, 240 Capsules

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