chapter  4
24 Pages

- Vitamin E

Vitamin E is unique because it remains a vitamin without a specic function, other than its action as a lipid-soluble antioxidant. Other vitamins are cofactors, are hormones, or have specic roles in metabolism. Vitamin E deciency symptoms are varied and dependent upon tissue α-tocopherol content, uptake and turnover, as well as susceptibility to and the degree of oxidative stress in a given

4.1 Introduction .......................................................................................................................... 125 4.2 History .................................................................................................................................. 126 4.3 Structures and Antioxidant Chemistry ................................................................................. 126

4.3.1 Structure ................................................................................................................... 126 4.3.2 Nomenclature ............................................................................................................ 127 4.3.3 Chemical Properties ................................................................................................. 127 4.3.4 Antioxidant Network ................................................................................................ 128 4.3.5 Oxidized Vitamin E .................................................................................................. 128

4.4 Physiologic Relationships ..................................................................................................... 128 4.4.1 Absorption ................................................................................................................ 128 4.4.2 Lipoprotein Transport ............................................................................................... 129 4.4.3 Tissue Delivery ......................................................................................................... 129 4.4.4 Storage Sites .............................................................................................................. 130

4.5 Vitamin E-Specic Proteins ................................................................................................ 130 4.5.1 α-Tocopherol Transfer Protein .................................................................................. 130 4.5.2 Other Tocopherol Binding Proteins .......................................................................... 131

4.6 Plasma Vitamin E Kinetics ................................................................................................... 132 4.7 Metabolism and Excretion .................................................................................................... 132 4.8 Cellular and Biochemical Functions ..................................................................................... 134 4.9 Nutritional Requirement ....................................................................................................... 135

4.9.1 Adequacy of Vitamin E Intakes in Normal US Populations .................................... 136 4.9.2 Food Sources of Vitamin E ...................................................................................... 136

4.10 Deciency Signs and Methods of Nutritional Assessment ................................................... 137 4.10.1 Vitamin E Deciency Caused by Genetic Defects in the α-Tocopherol Transfer

Protein ....................................................................................................................... 137 4.10.2 Vitamin E Deciency Caused by Genetic Defects in Lipoprotein Synthesis........... 138 4.10.3 Vitamin E Deciency as a Result of Fat Malabsorption Syndromes ....................... 138 4.10.4 Pathology of Human Vitamin E Deciency ............................................................. 138 4.10.5 Assessment of Vitamin E Status ............................................................................... 139

4.11 Efcacy of Pharmacological Doses of Vitamin E ................................................................ 139 4.12 Conclusion ............................................................................................................................ 140 Acknowledgments .......................................................................................................................... 140 References ...................................................................................................................................... 141

organ. Furthermore, vitamin E concentrations depend upon the presence of other antioxidants to maintain α-tocopherol in its unoxidized state (Buettner 1993).