ABSTRACT Accurate dietary assessment of vitamin K requires representative food composition data for specific geographical regions. The purpose of this study was to determine the contents of 3 different forms of vitamin K (phylloquinone [K1], 2′,3′-dihydrophylloquinone [dK], and menaquinone-4 [MK-4]) in representative grains, cereals, and baked goods, including breakfast foods, in the U.S. food ... [Show full abstract] supply. Samples were obtained as part of USDA's Natl. Food and Nutrient Analysis Program and analyzed by high-performance liquid chromatography (HPLC). Overall, breads, grains, and breakfast cereals were limited sources of K1 (range: nondetectable [ND] to 11.2 μg/100 g), with a wide range in dK (range: ND to 47.0 μg/100 g). In contrast, processed foods, such as fast-food breakfast sandwiches and baked goods, contain wide ranges of K1 (0.9 to 39.3 μg/100 g) and dK (ND to 72.2 μg/100 g). For any given food, K1 concentrations clustered within a narrow range, whereas dK concentrations had a wide range for a given food, suggestive of divergent use of hydrogenated oils in the manufacturing process. Low MK-4 concentrations (1.8 to 4.0 μg/100 g) were detected in meat- and cheese-containing breakfast foods and certain pie crusts. These data suggest that processed foods that contain K1-rich plant oils are a source of K1 and dK in the U.S. food supply.