Vitamin K2 Needs an RDI Separate from Vitamin K1

Abstract

Vitamin K and its essential role in coagulation (vitamin K [Koagulation]) have been well established and accepted the world over. Many countries have a Recommended Daily Intake (RDI) for vitamin K based on early research, and its necessary role in the activation of vitamin K-dependent coagulation proteins is known. In the past few decades, the role of vitamin K-dependent proteins in processes beyond coagulation has been discovered. Various isoforms of vitamin K have been identified, and vitamin K2 specifically has been highlighted for its long half-life and extrahepatic activity, whereas the dietary form vitamin K1 has a shorter half-life. In this review, we highlight the specific activity of vitamin K2 based upon proposed frameworks necessary for a bioactive substance to be recommended for an RDI. Vitamin K2 meets all these criteria and should be considered for a specific dietary recommendation intake.

Keywords: RDI; menaquinone; vitamin K; vitamin K-dependent proteins; vitamin K1; vitamin K2.

Figure 1

Name, structure, K1/2, T1/2, and main sources of vitamin K1 and major vitamin K2 isoforms [25].

Figure 2

Intake of vitamin K and percentage of total absorbed vitamin K based upon estimated approximations of levels of vitamin K in the Western diet and previously determined absorption values. Given that VK1 is only 10–15% absorbed and that VK2 analogs are more completely absorbed, actual vitamin K levels vary significantly compared to the food content. Further to this, consumption of VK2 isoforms MK-7, -8, and -9 contributes to the majority of extrahepatic processes regulated by VKDPs.