Vitamin KIs vitamin K safe?
Short answer
Yes, for most people. Neither the US nor the EU has set an upper limit for vitamin K.[1][2] US experts found no reports of harm from vitamin K in food or supplements.[1] A 2017 safety review found no serious risk from MK-7 supplements.[3] In pregnancy the US adequate intake is the same as for other adult women: 90 µg a day.[1]
The main risk is for people who take warfarin or a similar blood thinner. Vitamin K works against these medicines, so a sudden change in intake can make them work more or less strongly.[1] The authors of one study warned that 50 µg of MK-7 a day or more may change their effect.[4] Vitamin K3 (menadione) is no longer used in supplements, because it damaged liver cells in lab studies.[1]
Sources (4)
- Vitamin K: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
- Dietary reference values for vitamin K. European Food Safety Authority, 2017. efsa.onlinelibrary.wiley.com
- US Pharmacopeial Convention safety evaluation of menaquinone-7, a form of vitamin K. Marles RJ, Roe AL, Oketch-Rabah HA Nutr Rev, 2017. PMID 28838081
- Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Schurgers LJ, Teunissen KJ, Hamulyák K, Knapen MH, Vik H, Vermeer C Blood, 2007. PMID 17158229
More about vitamin k
What is vitamin K?Which foods contain vitamin K?What is vitamin K used for?Who is at risk of vitamin K deficiency?Why do newborn babies get vitamin K?Does vitamin K help keep bones strong?For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.