M F Picciano, National Institutes of Health, Bethesda, MD, USA
S S McDonald, Raleigh, NC, USA © 2005 Elsevier Ltd. All rights reserved.
A dietary supplement is a product that is intended to supplement the diet and contains at least one or more of certain dietary ingredients, such as a vitamin, mineral, herb or other botanical, or an amino acid. These products may not be represented as conventional foods; rather, they are marketed in forms that include capsules, tablets, gelcaps, soft-gels, and powders. Although manufacturers must have evidence to support their claims of a dietary supplement's safety and efficacy, US Food and Drug Administration (FDA) approval is not required before a product is marketed. Micronutrient dietary supplements (vitamins and minerals for purposes of this discussion) are commonly purchased and consumed in developed countries, even though taking greater quantities of micronutrients than recommended may not have proven benefits for the general population and, for some micronutrients (e.g., vitamin A), may have harmful effects. It may seem logical to assume that the majority of people who live in developed countries can use food sources to obtain the amounts of micronutrients required to maintain overall good health. However, the possibility of helping to prevent chronic diseases through micronutrient supplementation is attracting the interest of many people. A rigorous research approach must be used to determine in what circumstances micronutrient dietary supplements can have beneficial, including preventive, health effects. Special attention must be given to possible differences in micronutrient requirements at different life cycle stages. These stages include infancy (birth to 12 months), childhood (1-18 years), adulthood, and older adulthood (70 years and older). Evidence supporting dietary supplementation at different lifestyle stages is summarized here for several micronutrients.
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