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