Vitamin E Pharmacokinetics And Biomarkers In Normal And Obese Women

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Explanation Vitamin E (alpha-tocopherol) is essential for humans, but lack of a specific -tocopherol-dependent pathway has made setting human dietary requirements difficult. The recommended dietary allowance (RDA) for vitamin E will have to be carefully revised when it is next due for review. Approximately 96% of American women do not meet the 2000 recommendation, although without apparent harm. No new data are currently available, and this study seeks to fill the gap. Accurate alpha-tocopherol requirements may improve the health of women, especially obese women who experience high levels of inflammation and oxidative stress, because vitamin E is an antioxidant. We hypothesize that alpha-tocopherol functions as an antioxidant as related to its tissue stores in normal weight and obese women; that delivery to tissue stores can be calculated from plasma alpha-tocopherol turnover kinetics from slow release pools; and that turnover kinetics are a new means to estimate an alpha-tocopherol recommended dietary allowance. 1. Evidence indicates that the most relevant alpha-tocopherol parameters are those from the slow release pools. Therefore, these will be characterized using dual stable-isotope labeled (deuterium) alpha-tocopherols administered orally and intravenously to healthy lean and obese women. Because ascorbic acid (vitamin C) concentrations may alter alpha-tocopherol pharmacokinetics, subjects will be studied first at low and then high steady state vitamin C concentrations. Before this main study is initiated, two preliminary trials will be performed. a. In preliminary trial 1, fat content for optimal absorption will be assessed because fat-content of a meal may alter vitamin E absorption. The fat content will be 0 - 40% of calories in the breakfast meal. Carbohydrate and fat will vary, and protein will remain constant. Remaining meals during test days will not be restricted in fat. A single vitamin E dose of 30 mg will be given orally and intravenously. b. In preliminary trial 2, optimal fat content from preliminary trial 1 will be used, and the vitamin E dose will be varied. Vitamin E dose amount could non-specifically alter vitamin E kinetics. We will therefore determine the largest dose (2-30 mg) that does not non-specifically increase vitamin E turnover, with fat held constant. 2. Measures of alpha-tocopherol pharmacokinetics, as a function of lipid peroxidation biomarkers, will provide direct data that can be used for the first time to predict alpha-tocopherol requirements for women and set new recommendations for vitamin E intakes. These experiments will provide turnover data, essential for making new alpha-tocopherol RDAs. 3. We will explore new alpha-tocopherol functions, specifically whether gene transcription in human subjects is regulated by vitamin E status in relation to vitamin C status, and whether single nucleotide polymorphisms (SNPs) exist in relevant genes and perhaps account for inter-individual differences in vitamin E metabolism and pharmacokinetics. 4. Because vitamin E turnover may be affected by vitamin C concentrations, we will use a vitamin C depletion-repletion study design to investigate the relationship between vitamin C status and vitamin E turnover. Preliminary trial one commenced at the end of 2014 and is on-going.