GradedHealth

Vitamin K2

Last reviewed October 2026 · Based on 16 studies

Bottom line

Vitamin K2 may help keep spine bone density up in postmenopausal women, but fracture results are mixed and the artery studies are small and do not agree. No serious side effects were reported, though adverse reactions were more common in some pooled analyses.

What it helps with

  • Builds bone density — Benefit, evidence grade C (Limited). Meta-analyses of 9 to 16 RCTs show lumbar gains, but two well-run trials found none; downgraded for inconsistency and because bone density is a surrogate marker.
  • Prevents fractures — Mixed results, evidence grade B (Moderate). Meta-analyses of RCTs disagree: the pooled result is not significant, and a significant result appears only after excluding a heterogeneous trial; downgraded once for inconsistency.
  • Causes side effects — Mixed results, evidence grade B (Moderate). Pooled analyses disagree on whether adverse reactions are more common; no serious adverse events reported; downgraded once for inconsistency.
  • Slows arterial calcification — Mixed results, evidence grade C (Limited). Small RCTs using calcification imaging as the outcome; one positive two-year trial, one null two-year trial, and one non-significant trend; downgraded for inconsistency and surrogate outcome.

What it is

Vitamin K2 is a group of forms of vitamin K. Trials have used menaquinone-7 (MK-7), a form found in natto, and menatetrenone [1][2][3].

How it might work

Proposed mechanism: vitamin K helps activate osteocalcin, a protein that binds to bone mineral [4]. Vitamin K is also thought to help block calcium from building up in arteries [5].

What the research says

Pooled trials of 16 studies with 6,425 people found a significant improvement in lumbar spine bone density [4]. A second meta-analysis of nine trials found a lumbar gain of 2.17 percentage points (95% CI 1.59 to 2.76) [6]. Single trials disagree: one three-year trial of 244 women found slower bone loss at the lumbar spine and femoral neck [7], while a 12-month trial of 334 women found no difference [1]. Fracture results are not clearly positive: overall risk ratio 0.96 (P = 0.65) across six trials [4], and vertebral fracture risk ratio 0.87 (0.64 to 1.20) for menatetrenone [3]. For arteries, MK-7 slowed coronary calcium growth in one two-year trial of 180 people [2], but showed no difference in aortic valve calcification in 365 men [5].

Doses used in studies

MK-7 was given at 360 µg a day in coronary calcification trials [2][8], at 375 µg a day in a bone microarchitecture trial [9], and at 720 µg a day with 25 µg of vitamin D in an aortic valve trial [5]. A Chinese trial used menatetrenone at 45 mg a day [10].

Safety and interactions

Side effects: pooled analyses found higher rates of adverse reactions with vitamin K2 (risk ratio 1.33, 1.11 to 1.59), with no serious adverse events related to it [6]. Menatetrenone was linked to more adverse drug reactions (risk ratio 1.29, 1.07 to 1.56) [3]. Kidney: no serious adverse events were seen in a 24-week trial in people on haemodialysis [11]. Blood thinners: a 2016 review of dietary vitamin K and warfarin found conflicting evidence and advised against restricting vitamin K-rich foods, but it excluded supplements [12]. Our searches did not find studies on the upper intake limit, pregnancy or breastfeeding, so check those with a doctor.

Caveats and open questions

Pooled bone results mix several forms of vitamin K2, and one fracture result depends on dropping a trial [4][3]. Arterial trials are small, use calcification imaging as their outcome, and disagree with each other [2][5][8].

References

  1. Vitamin K2 supplementation does not influence bone loss in early menopausal women: a randomised double-blind placebo-controlled trial.. Osteoporos Int, 2010.
  2. Two Years of Menaquinone-7 Supplementation and Coronary Artery Calcification: A Randomized Clinical Trial.. JAMA Cardiol, 2026.
  3. The efficacy and safety of menatetrenone in the management of osteoporosis: a systematic review and meta-analysis of randomized controlled trials.. Osteoporos Int, 2019.
  4. Efficacy of vitamin K2 in the prevention and treatment of postmenopausal osteoporosis: A systematic review and meta-analysis of randomized controlled trials.. Front Public Health, 2022.
  5. Vitamin K2 and D in Patients With Aortic Valve Calcification: A Randomized Double-Blinded Clinical Trial.. Circulation, 2022.
  6. Efficacy and safety of vitamin K2 for postmenopausal women with osteoporosis at a long-term follow-up: meta-analysis and systematic review.. J Bone Miner Metab, 2022.
  7. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women.. Osteoporos Int, 2013.
  8. The effect of menaquinone-7 supplementation on vascular calcification in patients with diabetes: a randomized, double-blind, placebo-controlled trial.. Am J Clin Nutr, 2019.
  9. Vitamin K2 (menaquinone-7) prevents age-related deterioration of trabecular bone microarchitecture at the tibia in postmenopausal women.. Eur J Endocrinol, 2016.
  10. Menatetrenone versus alfacalcidol in the treatment of Chinese postmenopausal women with osteoporosis: a multicenter, randomized, double-blinded, double-dummy, positive drug-controlled clinical trial.. Clin Interv Aging, 2014.
  11. Effect of Menaquinone-7 Supplementation on Arterial Stiffness in Chronic Hemodialysis Patients: A Multicenter Randomized Controlled Trial.. Nutrients, 2023.
  12. Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True?: A Systematic Review.. Medicine (Baltimore), 2016.