Vitamin K2
Menaquinone
Key Benefits
Bone Mineralization
Activates osteocalcin, a protein that binds calcium to the bone matrix, improving bone density.
Cardiovascular Health
Activates Matrix Gla-protein (MGP), preventing calcium deposits in arteries and soft tissues.
Activation Synergies
Vitamin D increases calcium absorption; K2 ensures proper calcium distribution to bones vs. arteries.
Recommended Dosage
medical_servicesMK-7 form has longer half-life and better bioavailability than MK-4. Take with fats for absorption.
Deficiency Indicators
- Easy bruising or bleeding
- Osteoporosis or low bone density
- Arterial calcification (detected via imaging)
Scientific Citations
Vitamin K: Research Summary
Research & Sources
What the evidence says — with links to the original studies
Vitamin K2 (menaquinone) is a cofactor for the enzyme that carboxylates (activates) vitamin K-dependent proteins, most notably osteocalcin in bone and matrix Gla protein (MGP) in the arterial wall. Carboxylated osteocalcin binds calcium into the bone matrix, while carboxylated MGP inhibits calcium deposition in soft tissue, giving K2 a biologically plausible dual role in supporting bone density and limiting vascular calcification. The strongest human evidence comes from the long-chain form MK-7, which has a markedly longer half-life and greater bioavailability than MK-4 at nutritional doses. Two well-known Dutch trials by Knapen et al. showed that 180 micrograms MK-7 daily for three years reduced the age-related decline in lumbar spine and femoral neck bone mineral density (2013) and improved arterial stiffness (cfPWV, Stiffness Index beta) in healthy postmenopausal women (2015). Observational data (the Rotterdam Study) linked higher dietary menaquinone intake to lower coronary heart disease risk and reduced aortic calcification. Meta-analyses report positive effects on lumbar-spine BMD and undercarboxylated osteocalcin, and possibly reduced fracture risk, but the bone evidence base is dominated by Japanese trials (many using high-dose MK-4, 45 mg/day, sometimes as the drug menatetrenone) and results in Western populations are more mixed — including a well-conducted 3-year MK-7 RCT in osteopenic women that found no effect on BMD or microarchitecture despite improved osteocalcin carboxylation. K2 is frequently combined with vitamin D3, and reviews suggest combined K + D supplementation may outperform either alone, though the synergy is not conclusively established. Overall the mechanism is well characterized and biomarker effects (osteocalcin/MGP carboxylation) are robust, but hard clinical endpoints remain an emerging, not settled, area.
Supporting Evidence
Open access. MK-7 was well absorbed, peaked at 6 h, remained detectable up to 48 h and significantly raised serum levels; MK-4 at nutritional doses (420 ug single / 60 ug daily) was undetectable in serum. Supports MK-7's superior half-life/bioavailability and the rationale for preferring MK-7.
244 healthy postmenopausal women, 180 ug MK-7/day. Improved vitamin K status (ucOC/cOC ratio) and reduced age-related decline in bone mineral content and BMD at lumbar spine and femoral neck, but not total hip. Key bone-density RCT for MK-7. Abstract free; full text paywalled (PMID 23525894).
Same 180 ug MK-7/day cohort. Carotid-femoral pulse wave velocity and Stiffness Index beta significantly decreased vs placebo, with the largest benefit in women with the stiffest arteries at baseline; desphospho-uncarboxylated MGP dropped ~50%. A free repository version is available via Maastricht University CRIS.
~4,800 participants. Highest tertile of dietary menaquinone (K2) intake associated with lower coronary heart disease mortality, all-cause mortality and severe aortic calcification; no such association for phylloquinone (K1). Observational — hypothesis-generating, not causal. Full text open access via journal (S0022-3166(23)02896-1).
Open access. 16 RCTs, 6,425 subjects. Positive effect of K2 on maintenance/improvement of lumbar-spine BMD and reduced undercarboxylated osteocalcin; combination therapy (with D, calcium or bisphosphonates) stronger than K2 alone; good safety profile. Authors note the majority of included trials originated in Japan, limiting generalizability.
Open access. Reviews carboxylation of osteocalcin and matrix Gla protein as the mechanism; concludes combined vitamin D + vitamin K may be more effective than either alone for BMD, while noting limited added benefit alongside established osteoporosis drugs and calling for dosing/ratio studies. Supports the D3 synergy rationale.
Opposing / Critical Views
142 osteopenic postmenopausal women, 375 ug MK-7/day (plus D3 and calcium). Despite a 65% fall in undercarboxylated osteocalcin, MK-7 did NOT affect bone turnover markers, BMD or bone microarchitecture at any site (between-group p > 0.09). A well-conducted Western null RCT that tempers the positive Dutch findings (PMID 33030563).
Open access. 20 RCTs (~3,950 participants). Reported reduced vertebral and clinical fracture odds but a NON-significant effect on femoral BMD, and states evidence is insufficient to confirm K's therapeutic value for osteoporosis — a cautionary, mixed reading of the bone-density claim.
Full-text & official documents
- download Ma et al. (2022), Frontiers in Public Health — Efficacy of vitamin K2 in postmenopausal osteoporosis: systematic review & meta-analysis of 16 RCTs (open access)
- download Aaseth et al. (2024), Nutrients — Vitamin K and combined vitamins K and D for calcium metabolism and bone health: a review (open access)
- download Sato, Schurgers & Uenishi (2012), Nutrition Journal — Comparison of MK-4 and MK-7 bioavailability in healthy women (open access)
Educational summary of published research — not medical advice. Consult a qualified professional before supplementing.
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