Criteria and recommendations for vitamin C intake

Recommendations for vitamin C intake are under revision by the Food and Nut rition Board of the National Academy of Sciences, Since 1989 when the last recommended dietary allowance (RDA) of 60 mg was published, extensive bioch emical, molecular, epidemiologic, and clinical data have become available. New recommendations can be based on the following 9 criteria: dietary avail ability, steady-state concentrations in plasma in relationship to dose, ste ady-state concentrations in tissues in relationship to dose, bioavailabilit y, urine excretion, adverse effects, biochemical and molecular function in relationship to vitamin concentration, direct beneficial effects and epidem iologic observations in relationship to dose, and prevention of deficiency, We applied these criteria to the Food and Nutrition Board's new guidelines , the Dietary Reference Intakes, which include 4 reference values, The esti mated average requirement (EAR) is the amount of nutrient estimated to meet the requirement of half the healthy individuals in a life-stage and gender group, Based on an EAR of 100 mg/d of vitamin C, the RDA is proposed to be 120 mg/d, If the EAR cannot be determined, an adequate intake (AI) amount is recommended instead of an RDA. The AI was estimated to be either 200 mg/ d from 5 servings of fruits and vegetables or 100 mg/d of vitamin C to prev ent deficiency with a margin of safety, The final classification, the toler able upper intake level, is the highest daily level of nutrient intake that does not pose risk or adverse health effects to almost all individuals in the population. This amount is proposed to be less than 1 g of vitamin C da ily. Physicians can tell patients that 5 servings of fruits and vegetables per day may be beneficial in preventing cancer and providing sufficient vit amin C intake for healthy people, and that 1 g or more of vitamin C may hav e adverse consequences in some people.