Epidemiologic studies suggest that chronic disease risk can be reduced by a lifetime of consuming higher dietary vitamin E intakes. However, more than 90% of Americans consume less than 40% of the 15 mg (22 IU) 1-tocopherol recommended daily by the Food and Nutrition Board. Is the usual 6 mg consumed sufficient? The necessary evidence-based data are currently unavailable to answer this question;the proposed study seeks to fill this gap. Our previous studies show that oxidative stress in humans more rapidly depletes plasma vitamin E and sufficient vitamin C intake counters the accelerated vitamin E depletion. The proposed studies will use optimized methods for pharmacokinetic measurements to address how much vitamin E is needed by the body in response to either or both oxidative stress or depleted vitamin C status. This study is unique in that it is a collaboration between NIH intra- and extramural investigators. The proposed studies will be carried out with Dr. Mark Levine and his group at the NIH in the Clinical Research Center, who have extensive experience in measuring vitamin C pharmacokinetics and bioavailability. Our laboratory has the necessary expertise, experience and equipment to measure the low concentrations of stable isotope labeled vitamin E, its metabolites, and peroxidation biomarkers. This proposal seeks funding for the Traber group for the analysis of deuterium-labeled alpha-tocopherol samples and lipid peroxidation biomarkers.
Specific Aim 1. Determine alpha-tocopherol pharmacokinetics in normal weight women. Vitamin E kinetic studies will allow determination of key measures of vitamin E status including fractional absorption, rates of delivery to tissues, and whole body efflux. Pilot Study 1: Determine the optimal fat content in the accompanying meal necessary to optimize alpha-tocopherol absorption. Pilot Study 2: Determine the optimal alpha-tocopherol dose for turnover kinetics.
Specific Aims 2 &3. Determine alpha-tocopherol pharmacokinetics before and after vitamin C depletion in normal-weight women, obese women and obese women with diabetes. Our working hypothesis is that alpha-tocopherol concentrations are maintained by adequate vitamin C (ascorbic acid) concentrations. Thus, the delivery of alpha-tocopherol to the target tissues will be increased if ascorbic acid is limiting. Furthermore to maintain tissue alpha-tocopherol concentrations, rates of delivery of alpha-tocopherol increase due to increased turnover resulting from oxidative stress caused by obesity and from obesity with diabetes. The successful completion of these studies will provide essential key measures of alpha-tocopherol status, including fractional absorption, rates of delivery to tissues, and whole body efflux, for formulation of recommended daily intakes in healthy women, as well as women with conditions associated with increased oxidative stress.
We have shown that alpha-tocopherol is the most potent vitamin E form because the human body actively regulates its plasma concentrations and delivery to tissues while other vitamin E forms are actively metabolized and excreted. The proposed studies will use optimized methods for pharmacokinetic measurements and apply these to the problem of assessing """"""""how much vitamin E is needed by the body?"""""""", and do these needs change with increased oxidative stress or decreased vitamin C status.
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