What is vitamin K2 (MK-7)?
Vitamin K2 is a group of menaquinones that differ in the length of their side chain (MK-4 to MK-13). MK-7 is produced by bacteria, for example during the fermentation of natto, and stays in the blood much longer than vitamin K1.
What is vitamin K2 and what does MK-7 mean?
Vitamin K is a group of fat-soluble vitamins. K1 (phylloquinone) is found in green leafy vegetables. K2 (menaquinones, MK-n) is made by bacteria and occurs in fermented foods and animal products. The number after “MK” gives the side-chain length. MK-7 is particularly abundant in natto, fermented soybeans, and supplements commonly use MK-7 from natto fermentation.
Vitamin K is needed to activate certain proteins (carboxylation), including clotting factors and proteins in bone metabolism.
Why is MK-7 often highlighted?
In a study by Schurgers et al. (Blood, 2007) in healthy volunteers, MK-7 showed a very long half-life compared with K1. As a result, serum levels were steadier, and with prolonged intake MK-7 accumulated to about 7 to 8 times higher levels. K1, by contrast, is cleared within a few hours. A longer half-life, however, does not automatically mean a stronger effect in tissues.
Authorised claims and intake
In the EU the following claims are authorised for vitamin K: vitamin K contributes to normal blood clotting and to the maintenance of normal bones. The claims apply to vitamin K in general. The nutrient reference value (NRV) is 75 µg. EFSA sets the adequate intake for adults at 1 µg per kg body weight per day. Combinations with vitamin D3 are common; there is no separate authorised claim for the combination.
Vitamin K opposes vitamin K antagonists such as phenprocoumon (Marcumar) or warfarin. According to Schurgers et al. (2007), supplements providing 50 µg MK-7 per day or more may already affect such treatment in a clinically relevant way. If you take such anticoagulants, talk to your doctor before using any vitamin K supplement. This is general information, not medical advice. See also interactions.