Recommended Dietary Allowances (RDA) are used as the basis for decisions about the adequacy of food supplies, so it is important that the basis for establishing them and their limitations be clearly understood. As the concept of dietary allowances seems not to be generally well understood, I shall talk first about the general concept of RDA 1, 2 and then discuss the revision of the allowances for ascorbic acid.

Recommended Dietary Allowances are defined as “the levels of intake of essential nutrients considered, in the judgment of the Food and Nutrition Board on the basis of available scientific knowledge, to be adequate to meet the known nutritional needs of practically all healthy persons.” That is, they are recommendations for the quantities of a group of specific chemical compounds that should be consumed by each member of a population in order to provide reasonable assurance that the physiologic needs of all will be met. This is a public health concept. The RDA are nutritional standards. They are recommendations that can be used as the basis for practical decisions. They are standards designed to be used in planning the food supply of a population in order to ensure that the food procured will be nutritionally adequate to maintain the health of that population. They are standards also against which the nutritional adequacy of the available food supply can be assessed in order to identify possible nutrient shortages that could create public health problems. How are these standards established? The starting point is the quantitative information about human requirements. Two types of information are used for the most part:(1) information from studies on human subjects in which the amount of nutrient required for satisfactory growth, to maintain body weight, to prevent depletion of the nutrient from the body, to maintain some specific body function or to prevent the development of unique signs or symptoms has been established;(2) information from dietary surveys indicating how much of the nutrient is consumed by populations that are generally healthy and show none of the signs that are associated with an inadequate intake of the nutrient. From the first of these a figure for the average requirement of the population studied can be obtained; from the second, an estimate of the upper limit of human needs is obtained, but this may not be very precise. The upper limit of the requirement will usually be less than the average intake of a healthy population.