Dietary Reference Intakes for Calcium and Vitamin D (2011) / Chapter Skim
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1 Introduction
1 Introduction
Pages 15-34
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From page 15... ...
in Washington, DC, began an initiative to develop a new, broader set of values known as the Dietary Reference Intakes or DRIs (IOM, 2008)
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This committee's focus was, first, to review objectively the existing evidence concerning the benefits and health outcomes associated with vitamin D as well as calcium, using the well-established scientific principles for judging the quality and relevance of data from intervention as well as observational studies. The members of the committee next integrated the available data and, within the context of the risk assessment approach for establishing DRIs, carried out activities to specify DRIs for calcium and vitamin D
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Specifically, in carrying out its work, the committee was to: • Review evidence on indicators to assess adequacy and indicators to assess excess intake relevant to the general North American popu lation, including groups whose needs for or sensitivity to the nutri ent may be affected by particular conditions that are widespread in the population such as obesity or age-related chronic diseases. Special groups under medical care whose needs or sensitivities are affected by rare genetic disorders or diseases and their treatments were to be excluded; • Consider systematic evidence-based reviews, including those made available by the sponsors as well as others, and carefully document the approach used by the committee to carry out any of its own literature reviews; • Regarding selection of indicators upon which to base DRI values for adequate intake, give priority to selecting indicators relevant to the various age, gender, and life stage groups that will allow for the determination of an Estimated Average Requirement (EAR)
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Although the terminology associated with the discipline of risk analysis may at times be unfamiliar to those in the nutrition field, the discipline's structure and application are a good match for DRI development (Taylor, 2008)
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. Definition of Dietary Reference Intakes The DRIs are comprised of several reference values that relate to the concept of a distribution of requirements and a distribution of intakes.
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That was not the task of this committee for whom the focus has been the quantitative nutrient requirements and upper levels of intake. Currently, the mainstays of DRI development are the EAR, and the Tolerable Upper Intake Level, or UL (also referred to at times as Upper Levels of Intake)
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. Adequate Intake The possibility of the AI -- except for reference values for infants -- was not considered when the DRI framework was first developed in 1994 (IOM, 2008)
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The EAR is a reference value often important to the government sponsors of the report who may use requirement distributions to set national food policy, establish criteria for food programs, and make decisions about the adequacy of the food supply. An individual's nutrient requirement cannot be readily determined, and the use of DRIs for the purposes of assessing and planning diets of individuals is challenging.
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Children: Ages 1 Through 3 Years In terms of height, toddlers experience a faster growth rate compared with older children, and this distinction provides the biological basis for establishing separate recommended intakes for 1- to 3-year-olds compared with 4- to 8-year-olds. However, data on which to base DRIs for toddlers are often sparse; in many cases, DRIs must be derived by extrapolating data taken from the studies of infants or adults.
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From page 24... ...
For many nutrients, a reasonable number of data have been available on nutrient intake, and various criteria for adequacy serve as the basis for nutrient reference values for this group. For nutrients that lack data on the requirements of children in this age group, the nutrient reference values must be based on extrapolations from other life stage groups.
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Owing to the last two factors, for some nutrients there may not be a basis for setting reference values for pregnant or lactating women that differ from the values set for other women of comparable age. Indicators for DRI Development Indicators for DRIs are defined as the health outcomes that serve as the basis for estimating a nutrient requirement.
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. Given that the DRI development process couples the considerations for nutrient adequacy with those for excess intakes, there are advantages to applying the same organizing scheme for both ULs and EARs.
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One example is the procedures used for extrapolation relative to EAR and UL values. Study committees would likely notice potential incompatibilities if the evaluations for both adequate and excess intakes were compared in a side-by-side risk assessment framework.
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De novo literature reviews carried out as part of the study are well documented, including, but not limited to, information on search criteria, inclusion/exclusion criteria, study quality criteria, summary tables, and study relevance to the task at hand consistent with generally accepted methodology used in the systematic review process. • Identification of indicators to assess adequacy and excess intake Based on results from literature reviews and information gathering activities, the evidence is examined for potential indicators related to adequacy for requirements and the effects of excess intakes of the substance of interest.
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From page 29... ...
Step 3: Intake Assessment Consistent with risk assessment approaches, after the reference value is established, based on the information derived from scientific studies, an assessment of the current intake of (or exposure to) the nutrient of interest is carried out in preparation for the risk characterization step.
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The AHRQ-Ottawa and AHRQ-Tufts analyses represent the current thinking on approaches to developing dietary reference values in which expansive and at times conflicting bodies of evidence must be arrayed and evaluated in as objective a manner as possible. The key to ensuring the relevance of such analyses to the DRIs as well as their rigor and objectivity is to integrate subject matter experts with methodologists at the planning stages of the systematic reviews.
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But they do not and cannot establish nutrient reference values, nor do they replace the rigorous integration process and exercise of scientific judgment that characterizes DRI development. That process remains within the purview of the committee.
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The risk assessment approach begins with Chapter 4, which reflects a literature review and evaluation concerning potential indicators for development of DRIs for adequacy; at the close of the chapter, the indicator to be used for the development of DRIs for adequacy is identified. Chapters 5 through 8 contain discussions related to the other steps of risk assessment as specified in the generic model with Chapter 5 providing the reference values related to adequacy of calcium and vitamin D
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From page 33... ...
2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements.
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