1a. Objectives (from AD-416)
1. Determine the amounts of individual dietary forms of vitamin K in nationally representative samples of frequently consumed U.S. foods and dietary supplements. 2. Characterize the effects of dietary and non-dietary factors, such as age, lipid profile and body fat, on the bioavailability and utilization of different forms of vitamin K in humans. 3. Identify mechanisms of action for vitamin K, other than its classic role as an enzyme cofactor, using cellular and animal models.
1b. Approach (from AD-416)
Laboratory analysis of different forms of vitamin K will be conducted in selected foods obtained through collaboration with the USDA Nutrient and Data Laboratory (NDL), as part of the Food and Nutrient Analysis Program. Priorities for food analysis will include dietary supplements, food purchased in family style restaurants, foods common to the Hispanic/Latino diet, and foods associated with high calorie diets. Food composition data will be transferred to the NDL for entry into national food composition databases. To identify dietary and non-dietary factors that determine how much vitamin K obtained from foods is utilized, we will apply stable isotope techniques to measures of vitamin K metabolism. Data obtained from ongoing metabolic studies in men and women, in addition to pilot feasibility studies, will be used to refine the study design to test the response of these measures to intake of different vitamin K-rich food sources. Animal models will be used to identify tissue-specific effects of interactions between vitamin K and other fat-soluble vitamins, with an emphasis on vitamins A and D. To identify mechanisms of action for vitamin K other than its classic role as an enzyme cofactor, urinary and serum levels of vitamin K metabolites will be measured in response to vitamin K supplementation using archived samples from human and animal studies. We will then focus on the role of different forms of vitamin K in inflammation through the inactivation of nuclear receptors in macrophages.
3. Progress Report
To conduct studies for guidance on the health benefits of vitamin K, accurate and up-to-date food composition information is required. Foods obtained from restaurants and markets from various locations, including four Hispanic Community Health Study locations, were analyzed for vitamin K. Several foods were identified as important sources of dietary vitamin K, including plantain chips. Other foods, such as empanadas, show large variation in vitamin K content. The vitamin K food composition data were transferred to the Nutrient Data Laboratory at Beltsville Human Nutrition Research Center (BHNRC) for entry into the USDA National Nutrient Database for Standard Reference. These data will facilitate assessment of vitamin K status of Hispanics, which is the fastest growing minority group in the United States. To understand the benefits of an increased consumption of vitamin K on human health, we are studying the bioavailability and utilization of vitamin K. We will compare the effects of dietary and non-dietary factors, including age, lipid profile and body fat, on the utilization of vitamin K provided in the form of a green, leafy vegetable, in 42 younger and older men and women following 1-month periods of vitamin K depletion and vitamin K repletion, respectively. We have successfully completed the subject participation of this metabolic study, and are in the process of conducting laboratory analysis on biological samples collected over the duration of the study. Little is known about the metabolic fate of vitamin K following dietary intake. We applied novel stable isotope techniques to identify urinary vitamin K metabolites that can be used in bioavailability studies to indicate how much vitamin K is retained in the body following dietary intake. Using samples collected from previous human studies conducted in our laboratory, we identified a unique metabolite that is excreted in urine, and is a robust marker of dietary vitamin K depletion and repletion. This metabolite will also provide insight into mechanisms by which vitamin K is converted in the body from the forms present in plant foods to forms that have unique biological functions that may contribute to human health. For publications related to project, see parent project #1950-51000-069-00D.
1. Body Fat Stores Vitamin K and Reduces Its Availability for Important Body Functions It has been proposed that overweight and obese people store fat-soluble vitamins in their fat cells, and this storage can decrease these nutrients’ contribution to health. In contrast to vitamins A, D, and E, and carotenoids, little is known about the role of body fat in changing vitamin K functions. ARS-funded researchers from Tufts University in Boston, MA determined that vitamin K is stored in body fat. Furthermore, more body fat was associated with less vitamin K available to other organs. Moderate weight loss did not result in an improvement in vitamin K status. These findings suggest that obesity may attenuate the contribution of dietary vitamin K to human health.