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DRI DIETARY REFERENCE INTAKES FOR Vitamin C, Vitamin E, Selenium, and Carotenoids
it is critically important to conduct large-scale studies with children using state-of-the-art biomarkers to assess their vitamin E requirements.
Valid estimates are needed of vitamin E intakes. These estimates require identification of the specific fats and oils consumed, in addition to careful tabulation of all of the foods consumed, because the vitamin E content of various fats and oils differs widely and because vitamin E is widely distributed in many foods. Most individual foodstuffs consumed account for less than 1 percent of the daily intake of α-tocopherol. Calories are frequently underreported, as is dietary fat, and the form and quantity of fat consumed are unknown. Better methods for estimating vitamin E intakes are needed.
Information on the relationship between oxidative stress and vitamin E status is needed. Some information is available about the dosage of vitamin E needed to achieve plasma levels that protect circulating low-density lipoprotein (LDL) from ex vivo oxidation. However, there are scant data on tissue levels of vitamin E at different levels of intake. Do the large doses that confer protection of circulating LDL also confer protection within tissues against lipid peroxidation or other manifestations of reactive oxygen species generation? Are there markers of oxidative stress that can be related to vitamin E status?
Vitamin E kinetics and metabolism are promising areas of research. Can estimates of α-tocopherol requirements be made using stable isotopes? Are balance studies feasible that measure intake and output of stable isotope-labeled vitamin E? What is the turnover of α-tocopherol in various human tissues? In which tissues is it degraded and how rapidly? What are the major metabolic intermediates during degradation, and do they have biological function?
Determination of the effects of vitamin E intake on the prevention of chronic disease is needed. There is a great deal of suggestive or indirect evidence that vitamin E intakes above those that can reasonably be obtained from foods may confer health benefits. Before clinical intervention trials can be interpreted properly, more knowledge about the relationship of vitamin E dosage to level of protection, or level of protection to plasma cholesterol or lipoprorein levels, is needed. Additional clinical trials to test directly whether or not supplementation with vitamin E can reduce the risk of coronary heart disease are needed. A number of trials already in progress are evaluating vitamin E effects in well over 100,000 individuals. However, whether the results are positive or negative, additional studies will be needed. For example, if the results are negative, the question will arise of whether treatment was instituted early