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Vitamin K

Supplement Forms/Alternate Names

Vitamin K1 (phylloquinone), vitamin K2 (menaquinone), vitamin K3 (menadione)


Vitamin K is found in leafy greens, whole wheat, and oats. The body needs it for blood clotting and blood flow. Vitamin K has been used to clot blood and improve bone strength.

It can be taken as a pill or powder. It can also be injected into the bloodstream or muscle by a healthcare provider.


1 to 2 milligrams daily

What Research Shows

Unlikely to Be Effective

Not Enough Data to Assess

Editorial process and description of evidence categories can be found at EBSCO NAT Editorial Process.

Safety Notes

It is likely safe to take vitamin K in small doses for a short time. Not enough studies have been done to say whether it is safe to use for a long period.


Talk to your doctor about any supplements or therapy you would like to use. Some can interfere with treatment or make conditions worse, such as:

  • People taking blood thinners should talk to their doctors before taking vitamin K. It may interfere with the medicine.


A. Blood Clots

A1. Lam J, Schulman S, et al. Anticoagulation control with daily low-dose vitamin k to reduce clinically adverse outcomes and international normalized ratio variability: a systematic review and meta-analysis. Pharmacotherapy. 2013 Nov;33(11):1184-1190.

A2. Mahtani KR, Heneghan CJ, et al. Vitamin K for improved anticoagulation in patients receiving warfarin. Cochrane Database Syst Rev. 2014;(5):CD009917.

B. Bone Strength

B1. Cockayne S, Adamson J, et al. Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Arch Intern Med. 2006;166(12):1256-1261.

B2. Knapen MH, Schurgers LJ, et al. Vitamin K2 supplementation improves hip bone geometry and bone strength indices in postmenopausal women. Osteoporos Int. 2007;18(7):963-972.

B3. Iwamoto J, Sato Y, et al. High-dose vitamin K supplementation reduces fracture incidence in postmenopausal women: a review of the literature. Nutr Res. 2009 Apr;29(4):221-228.

B4. Stevenson M, Lloyd-Jones M, et al. Vitamin K to prevent fractures in older women: systematic review and economic evaluation. Health Technol Assess. 2009;13(45):iii-xi.

C. Cardiometabolic Risk Factors

C1. Verma H, Garg R. Effect of Vitamin K Supplementation on Cardiometabolic Risk Factors: A Systematic Review and Meta-Analysis. Endocr Metab Immune Disord Drug Targets. 2019;19(1):13-25.

D. Cardiovascular Disease

D1. Hartley L, Clar C, et al. Vitamin K for the primary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2015;(9):CD011148.

E. Cystic Fibrosis

E1. Jagannath VA, Fedorowicz Z, et al. Vitamin K supplementation for cystic fibrosis. Cochrane Database Syst Rev. 2011;(1):CD008482.

E2. Jagannath VA, Thaker V, et al. Vitamin K supplementation for cystic fibrosis. Cochrane Database Syst Rev. 2017 Aug 22;8:CD008482.

F. Osteoporosis

F1. Fang Y, Hu C, et al. Effect of vitamin K on bone mineral density: a meta-analysis of randomized controlled trials. J Bone Miner Metab. 2012 Jan;30(1):60-68.

F2. Huang ZB, Wan SL, et al. Does vitamin K2 play a role in the prevention and treatment of osteoporosis for postmenopausal women: a meta-analysis of randomized controlled trials. Osteoporos Int. 2015;26(3):1175-1186.

Last reviewed July 2019 by EBSCO NAT Review Board Eric Hurwitz, DC  Last Updated: 3/27/2020