Submitted to: American Journal of the Medical Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/1999
Publication Date: N/A
Interpretive Summary: Vitamin C (ascorbic acid, ascorbate) is an essential micronutrient involved in many biological and biochemical functions. Humans cannot synthesize vitamin C because of lack of gulonolactone oxidase, the last enzyme in the biosynthetic pathway. To avoid scurvy, humans must ingest vitamin C. Therefore, the Recommended Dietary Allowance (RDA) for vitamin C is an important guidepost for human needs. Recommendations for vitamin C intake are under revision by the Food and Nutrition Board of the National Academy of Sciences. Since the last recommendations for vitamin C intake issued in 1989, extensive biochemical, molecular, epidemiologic, and clinical data have been published. This article reviews the role of vitamin C in metabolic processes, discusses criteria used for recommended ingestion of vitamin C, and presents recommendations for vitamin C intake. Therefore, the information in this paper is useful to researchers who want to investigate the functional roles of vitamin C and provide data for recommendation of vitamin C intake. Also, this information is helpful to scientists who develop guidelines for recommendations for other nutrients.
Technical Abstract: Recommendations for vitamin C intake are under revision by the Food and Nutrition Board of the National Academy of Sciences. Since the recommendations of 1989, a wealth of biochemical, molecular, epidemiologic, and clinical data have become available. Based on these data, new recommendations can utilize the following nine criteria: dietary availability; steady-state concentrations in plasma in relation to dose; steady-state concentrations in tissues in relation to dose; bioavailability; urine excretion; adverse effects; biochemical and molecular function in relation to vitamin concentration; direct beneficial effects and epidemiologic observations in relation to dose; and prevention of deficiency. We applied these criteria to the Food and Nutrition Board's new guidelines on Dietary Reference Intakes. A new Recommended Dietary Allowance is proposed to be 120 mg daily, based on 100 mg as the new Dietary Reference Intake Classification Estimated Average Requirement. The new classification Adequate Intake, used when data are considered insufficient for a Recommended Dietary Allowance, was estimated to be either 200 mg daily from 5 servings of fruits and vegetables or 100 mg daily to prevent deficiency with a margin of safety. The new classification, Tolerable Upper Intake, is proposed to be less than 1 gram of vitamin C daily.