Vitamin K2 is a group of menaquinones, forms of vitamin K that differ by the length of a side chain. MK-7, the form in most K2 supplements, comes from natto (fermented soybeans).
Also known as: menaquinone-7, MK-7.
There is no separate intake value for K2. For vitamin K as a whole, ODS lists an Adequate Intake of 120 mcg a day for men and 90 mcg for women (ages 19 and up), and no upper limit, because of its low potential for toxicity.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. The FDA-approved vitamin K drug is phytonadione (vitamin K1), a tablet and an injection, which is a different form from K2.
ODS warns that vitamin K can have a serious interaction with blood thinners such as warfarin (Coumadin), and that people on warfarin need a consistent vitamin K intake. In a study comparing K1 with MK-7, Schurgers and colleagues (2007) concluded that 50 mcg a day or more of MK-7 may interfere with warfarin treatment in a clinically relevant way. If you take a blood thinner, talk to your prescriber before starting K2.
In a study comparing vitamin K1 with MK-7 (Schurgers 2007), both peaked about 4 hours after a dose, and MK-7 had a very long half-life, building up 7- to 8-fold with daily intake. Later studies found MK-7 peaked about 6 hours after a dose (Sato 2012) and reviews give a half-life of about 68 to 72 hours (Akbulut 2020). Dose Track uses 72 hours and 6 hours.
Numbers shown are the values Dose Track uses, listed only where they agree with the source above. Half-life varies from person to person and with injection site.