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Since the amount of vitamin K1 in typical diets is ten times greater than that of vitamin K2,20 researchers have tended to dismiss the contribution of K2 to nutritional status as insignificant. Yet over the last few years, a growing body of research is demonstrating that these two substances are not simply different forms of the same vitamin, but are better seen as two different vitamins: whereas K1 is preferentially used by the liver to activate blood clotting proteins, K2 is preferentially used by the other tissues to place calcium where it belongs, in the bones and teeth, and keep it out of where it does not belong, in the soft tissues.21 Acknowledging this research, the United States Department of Agriculture, in conjunction with researchers from Tufts University, finally determined the vitamin K2 contents of foods in the U.S. diet for the first time in 2006. Tweet