Fluctuations in international normalized ratio values are often ascribed to dietary changes in vitamin K intake. Here we present a database with vitamin K(1) and K(2) contents of a wide variety of food items. K(1) was mainly present in green vegetables and plant margarins, K(2) in meat, liver, butter, egg yolk, natto, cheese and curd cheese. To investigate the effect of the food matrix on vitamin K bioavailability, 6 healthy male volunteers consumed either a detergent-solubilized K(1) (3.5 micromol) or a meal consisting 400 g of spinach (3.5 micromol K(1)) and 200 g of natto (3.1 micromol K(2)). The absorption of pure K(1) was faster than that of food-bound K vitamins (serum peak values at 4 h vs. 6 h after ingestion). Moreover, circulating K(2) concentrations after the consumption of natto were about 10 times higher than those of K(1) after eating spinach. It is concluded that the contribution of K(2) vitamins (menaquinones) to the human vitamin K status is presently underestimated, and that their potential interference with oral anticoagulant treatment needs to be investigated.