Benefits
Carboxylates osteocalcin in bone tissue
Osteocalcin has to be carboxylated by a vitamin K dependent enzyme before it can bind calcium into the bone matrix. Vitamin K reliably lowers undercarboxylated osteocalcin, and this is the one effect that repeats from trial to trial, including those where bone density itself did not budge.
Studied at drug-level doses for fracture risk
Japanese trials of 45 mg a day in people with osteoporosis reported fewer new fractures and better-maintained spinal bone density, and an early pooled analysis echoed that. A much larger later Japanese trial at the same dose did not reduce vertebral fractures overall. Nothing in this literature applies to microgram supplement doses.
Bone mineral density outcomes in Western trials
A twelve-month randomized trial in healthy postmenopausal North American women using the same 45 mg dose reduced undercarboxylated osteocalcin but changed nothing about bone turnover, density or geometry at the spine or hip. The authors concluded the data do not support vitamin K for osteoporosis prevention in that population.
Tissue-level vitamin K activity via UBIAD1
The body converts K1 and other menaquinones to MK-4 inside tissues that need it, which is why MK-4 concentrates in bone, brain and arterial wall rather than the liver. This explains the interest in the form, but it also means normal K1 intake already supplies tissue MK-4.
Mechanism of action
Gamma-glutamyl carboxylase cofactor
Vitamin K hydroquinone is the cofactor for gamma-glutamyl carboxylase, which converts glutamate residues on osteocalcin, matrix Gla protein and the clotting factors into calcium-binding gamma-carboxyglutamate. The vitamin K epoxide reductase cycle then regenerates it.
UBIAD1-mediated tissue conversion
UBIAD1 was identified as the human enzyme that replaces the side chain of phylloquinone or menadione with a geranylgeranyl group to produce MK-4 directly inside target tissues. This is why MK-4 is the dominant vitamin K form in bone, brain and pancreas.
Matrix Gla protein and vascular calcium
Carboxylated matrix Gla protein binds calcium in the arterial wall and restrains its deposition into soft tissue. Undercarboxylated matrix Gla protein tracks with vascular calcification, which is the basis for cardiovascular interest in vitamin K, mostly studied with MK-7 rather than MK-4.
Short plasma half-life
MK-4 clears from plasma within a few hours, unlike MK-7, which persists for days. That pharmacokinetic gap is why Japanese protocols split 45 mg across three daily doses and why low-dose MK-4 supplements do not produce a measurable rise in serum MK-4.
Clinical trials
Randomized controlled trial of 45 mg/day menatetrenone over 24 months (Shiraki M, Shiraki Y, Aoki C, Miura M 2000, J Bone Miner Res 15(3):515-21, PMID 10750566).
241 patients with osteoporosis, 120 treated and 121 controls, followed for 24 months.
Fracture incidence was higher in the control group than in the treated group (p=0.0273), and lumbar bone mineral density was sustained rather than increased. The authors concluded menatetrenone effectively prevents new fractures while failing to raise lumbar density. The dose used is a prescription drug dose in Japan, not a supplement dose.
Phase IV randomized controlled study of 15 mg menatetrenone capsules for osteoporotic fracture prevention (Inoue T, Fujita T, Kishimoto H, Makino T, Nakamura T, Nakamura T, Sato T, Yamazaki K 2009, J Bone Miner Metab 27(1):66-75, PMID 19082528).
4,378 patients randomized to menatetrenone monotherapy or combined therapy, followed for 36 months.
The incidence of new vertebral fractures over 36 months did not differ significantly between groups. The authors concluded menatetrenone was not effective for preventing vertebral fractures in the full analysis set, while suggesting a possible effect in patients with more advanced osteoporosis. This is the largest trial of the form and it did not meet its endpoint.
Twelve-month randomized trial of phylloquinone 1 mg/day or MK-4 45 mg/day (Binkley N, Harke J, Krueger D, Engelke J, Vallarta-Ast N, Gemar D, Checovich M, Chappell R, Suttie J 2009, J Bone Miner Res 24(6):983-91, PMID 19113922).
381 healthy postmenopausal North American women, all receiving calcium and vitamin D.
Both forms lowered undercarboxylated osteocalcin, but neither changed bone turnover markers or bone mineral density at the lumbar spine or proximal femur. The authors concluded the study does not support a role for vitamin K supplementation in osteoporosis prevention among healthy postmenopausal women already taking calcium and vitamin D.