Purpose: The goal of this report is to review the dietary requirements, including the physiological roles and recommended intakes, of vitamins and minerals in human nutrition. The report is composed of several chapters. This summary will focus on the first introductory chapter, Concepts, definitions and approaches used to define nutritional needs and recommendations. Information from this report for specific micronutrients is reviewed in the individual summaries for each nutrient.
Introduction to Dietary Requirements of Vitamins and Minerals
- The dietary requirement of any given micronutrient (vitamin or mineral) is the intake level that is required to be adequate and which minimizes a deficit or excess of that nutrient. Adequacy depends on the following:
- The dietary intake required to prevent death either due to a deficiency or to an excess
- The dietary intake required to prevent clinical diseases and subclinical conditions due to a deficiency
- The nutritional needs across age ranges, sex, and physiological states
- Variations in micronutrient bioavailability and utilization
- Assessment of micronutrient status is generally done using functional assays or biomarkers.
- Appropriate biomarkers must be both sensitive to changes in a given micronutrient and specific to the nutrient that is responsible for the subclinical conditions. It is often difficult to have a biomarker that is both sensitive and specific to a particular nutrient deficiency. For example:
- Low serum ferritin is a sensitive indicator for iron deficiency; however it is not specific to iron deficiency. Serum ferritin concentrations change due to iron status, but also change due to acute infections or inflammatory processes.
- Anemia is an indicator used for iron deficiency, but it is not specific to inadequate iron. Folate, vitamin B12, and copper deficiencies are all independent causes of anemia.
Select Terms Used to Describe Dietary Requirements: The following are terms that are commonly used when discussing the recommended intakes for individual nutrients.
- Estimated Average Requirement (EAR):
- The EAR is defined as the average daily intake that meets the needs of 50% of the healthy individuals within an age- and sex- specific population.
- Recommended Nutrient Intake (RNI):
- The RNI is defined as the daily dietary intake that meets the nutrient requirement of almost all (i.e., 97.5%) apparently healthy individuals in a particular age- and gender- specific population.
- The RNI is the same as the recommended dietary allowance (RDA) that is use by the Food and Nutrition Board of the United States National Academy of Sciences.
- Tolerable Upper Limit (UL):
- The UL is the maximum amount of daily intake from food, water, and supplements that does not have a risk for adverse health effects in almost all (i.e., 97.5%) apparently healthy individuals within an age- and sex- specific population.
Dietary Intake Assessments
- Assessment of dietary intake should include food water and supplements.
- Dietary intakes vary day-to-day, and therefore, daily requirements refer to the average intake over several days.
- Using the dietary recommendations for individuals:
- The RNI and UL are used to define intakes for populations rather than individuals. However, intakes between the RNI and the UL should be sufficient to prevent both a nutrient deficiency and a nutrient excess in healthy individuals.
- The dietary recommendations based on the RNI and UL may not meet the requirements for individuals and populations who are not considered healthy. Nutrient recommendations for these individuals will need to be adjusted based on the special needs of their disease or environmental conditions.
- Using the dietary recommendations for populations:
- The EAR (not RNI) should be used to assess the dietary intakes of any given population group.
- When estimating the prevalence of a deficiency based on the intake in a population, the prevalence is defined as the proportion of the population who are below the EAR.
- Intakes between the EAR and UL are considered acceptable intakes for a population.
- RNIs are important in defining adequate intakes for vitamins and minerals. However, RNIs alone (or single-nutrient approaches) are not useful in implementing public health programs aimed at improving nutrition in populations.
- The use of food-based dietary guidelines (FBDGs) for public health programs is more effective in addressing diet-health relationships within a particular country or region.
- FBDGs consider the cultural dietary patterns, the foods available, and the factors that determine the consumption of foods within a region. Using this information, FBDGs identify which of these aspects should be modified to improve the nutrition within that region.
- RNIs and FBDGs are used together in public health programs aimed at improving nutrition. RNIs, and the empirically defined nutrient requirements, are used to develop the FBDGs. The FBDGs then take into account the dietary patterns, the socioeconomic and cultural factors, and the biological and physical environments which affect the health and nutrition of a community to design and implement public health programs aimed at improving nutrition.
Reference: Concepts, definitions and approaches used to define nutritional needs and recommendations. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004:1-16.