Handbook of Vitamin C Research

Human Specific Vitamin C Metabolism… 49vivo studies [4, 5, 8] are needed to determine nutritional requirement of VC and to elucidatethe effects of polymorphisms in xenobiotic enzymes [4, 5].(2) Recommended Dietary Allowances (RDA) for VC and Optimal NutritionThe recommended dietary allowance (RDA) is based on the estimated averagerequirement (EAR: the intake sufficient to satisfy the needs of 50% of the subjects and thestandard deviation (SD) obtained by balancing studies on large numbers of subjects [28].Therefore, RDA (defined as EAR+2SD) is intended to cover the nutritional requirements of97.5% of subjects. In May 2005, RDAs for VC as part of ―Dietary Reference Intakes forJapanese, 2005‖ were released by the Ministry of Health, Labor, and Welfare, Japan [28]. Forboth men and women from 12 years to over 70 years, an EAR of 85 mg/day was determinedfrom depletion–repletion data [28]. On the basis of this value, considering the coefficient ofvariation (SD/EAR = 10 %) for interindividual difference, an RDA of 100 mg/day (RDA =EAR+2SD) was derived for both men and women from 12 years to over 70 years [28].Because similar data were not available for children, an EAR had to be extrapolated on thebasis of standard body weight differences and growth factors [28]. RDAs for VC are 90mg/day for men and 75 mg/day for women in U. S. A. (RDA 2000, for detailed recent values,see section (9) of discussion) [29].However, Pauling pointed out that the RDA is less than the optimum intake,corresponding to the best health [30]. Based on synthetic rates of VC in rat, 58mg/day/kgbody weight, he concluded that the optimum daily intake is about 2.3 g or more, for an adultwith energy requirement 2500 kcal/day [30]. This is the problem of RDA vs. optimalnutrition [31]. Optimal nutrition for VC covers wider scope than RDA due to the followingthree reasons: polymorphism, long-term outcome and xenobiotics [31].Polymorphism: The statistics of the RDAs assumes nearly normal distribution of the data[28], which is not always true in populations composed of many genetic polymorphisms[5, 8, 31]. For example, the guideline recommends ethanol intake