Is Vitamin K2 an Essential Nutrient?
Vitamins K1 and K2 are both effective cofactors for the enzyme that activates vitamin K-dependent proteins,23 but the liver preferentially uses vitamin K1 to activate clotting factors while most other tissues preferentially use vitamin K2 to activate the other vitamin K-dependent proteins.21 Although animals can convert vitamin K1 to vitamin K2,14 there are a number of lines of evidence strongly suggesting that humans require preformed K2 in the diet to obtain optimal health. Humans appear to have a finite ability to absorb vitamin K1 from plant foods. In the United States, where the mean intake of vitamin K1 is less than 150 micrograms per day, blood levels increase with increasing dietary intake until the latter reaches two hundred micrograms per day, after which they plateau. In the Netherlands, where the mean intake of vitamin K1 is much higher (250 micrograms per day), plasma levels of vitamin K1 have no relationship to dietary intake at all.24 These results suggest that humans do
