Vitamin K2 MK-4 vs MK-7: Half-Life, Dose, and the Bone Trial Evidence

Vitamin K2 menaquinones come in subtypes named by the length of the isoprenoid side chain: MK-4 has four units, MK-7 has seven. Supplement labels rarely explain that the two forms have meaningfully different pharmacokinetics, different doses in trials, and a fundamentally different evidence base. A 45 microgram MK-7 capsule and a 45 milligram MK-4 capsule are not interchangeable.

Half-life and tissue distribution diverge sharply

Single-dose human pharmacokinetic work shows MK-7 has a serum half-life of about 68 hours, compared with roughly 1 to 2 hours for MK-4 [1]. The practical consequence is that low-dose MK-7 produces stable circulating levels with once-daily dosing, while MK-4 must be taken in much larger doses several times daily to reach measurable plasma levels [2]. MK-4 also concentrates preferentially in extrahepatic tissues such as pancreas and salivary gland, while MK-7 distributes more broadly to bone and vasculature.

The MK-4 bone trial record is built on 45 milligrams per day

Japanese osteoporosis trials going back to the late 1990s used 45 milligrams per day of synthetic MK-4 (menatetrenone), the dose at which it is licensed as a prescription drug in Japan. Pooled analyses of these trials report reduced fracture incidence, although a later large RCT (OF Study, 2009) found no significant fracture reduction in postmenopausal women without osteoporosis [3]. A 2006 meta-analysis by Cockayne and colleagues concluded that high-dose MK-4 modestly reduced vertebral fracture risk, but most included trials were Japanese and used the 45 mg pharmaceutical dose, not the microgram doses sold as supplements [4].

The MK-7 trial record looks bigger than it is

The most-cited MK-7 trial is Knapen and colleagues 2013, which randomized 244 postmenopausal women to 180 micrograms MK-7 daily for three years and found preserved vertebral bone mineral density and reduced height loss compared with placebo [5]. Vascular outcomes were tested in the same cohort, with reduced carotid arterial stiffness after three years of MK-7 supplementation [6]. These are positive surrogate-marker trials, but no MK-7 trial has demonstrated fracture reduction with hard outcomes, and head-to-head studies versus MK-4 do not exist.

Form interacts with vitamin K antagonist therapy

Both MK-4 and MK-7 will antagonize warfarin and other vitamin K antagonist anticoagulants. MK-7's long half-life makes INR stabilization especially difficult after introduction, and clinical case reports describe sub-therapeutic INRs from supplement initiation [7]. Patients on warfarin should not start either form without consulting the prescribing clinician.

What the comparison means in practice

The most defensible reading of the evidence is that MK-7 at 90 to 180 micrograms per day is supported by surrogate-marker trials for bone density and arterial stiffness, while MK-4 fracture-reduction evidence is largely confined to 45 mg pharmaceutical-dose Japanese trials and has not been replicated in Western populations. Both forms reach measurable carboxylation of matrix Gla protein, which is the surrogate vitamin K2 supplementation is built around [8]. Whether either form changes long-term cardiovascular or fracture endpoints in well-nourished adults remains an open question — the largest cardiovascular RCT (AVADEC) using high-dose MK-7 has so far reported no slowing of coronary calcification.