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DRI DIETARY REFERENCE INTAKES FOR Vitamin C, Vitamin E, Selenium, and Carotenoids
the selection of the degree of risk that can be tolerated when planning for the group (e.g., a 2 to 3 percent prevalence versus a higher or lower prevalence).
The effect of cigarette smoking on vitamin C status has led to recommending an increase to cover the higher vitamin C requirements for those who smoke. Thus, smoking status has to be considered in assessing and planning ascorbate intakes. Another consideration in evaluating vitamin C intake is the variability in the food supply and the loss during cooking of this water-soluble and heat-labile vitamin. Destruction of vitamin C in processing and cooking (Williams and Erdman, 1999) may be different than assumed by the values in the food composition tables resulting in an over- or under-estimation of the population at risk, while underreporting of dietary intakes in general may lead to an overestimate of the population at risk.
The Tolerable Upper Intake Level (UL) for vitamin C for adults is 2,000 mg/day. Sensitive individuals who regularly consume more than 2,000 mg/day may be at risk of osmotic diarrhea and gastrointestinal disturbances.
The Estimated Average Requirements (EARs), Recommended Dietary Allowances (RDAs), and Adequate Intakes (AIs) for vitamin E are based on α-tocopherol only and do not include amounts obtained from the other seven naturally occurring forms of vitamin E (β-, γ-, δ- tocopherol and the four tocotrienols). Although absorbed, these forms do not contribute to meeting the vitamin E requirement because they are not converted to α-tocopherol. Only the 2R-stereoisomeric forms of α-tocopherol are preferentially secreted by the liver into the plasma for transport to tissues. Since the 2S-stereoisomeric forms of α-tocopherol are not maintained in human plasma or tissues, vitamin E is defined in this report as limited to the 2R-stereoisomeric forms of α-tocopherol to establish recommended intakes. However, all eight stereoisomers of supplemental α-tocopherol are used as the basis for establishing the Tolerable Upper Intake Level (UL) for vitamin E.
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