Harmonization of Approaches to Nutrient Reference Values Applications to Young Children and Women of Reproductive Age (2018) / Chapter Skim
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3 A Harmonized Process for Nutrient Reference Value Development
3 A Harmonized Process for Nutrient Reference Value Development
Pages 41-72
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From page 41... ...
In this chapter, the committee examines and assesses in greater detail key steps in the nutrient review process, with a focus on how to assess relevant data from systematic reviews and other data resources and how to account for local context (e.g., culturally specific food choices and dietary patterns)
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In the figure, the option to update or adapt existing NRVs means that it is not necessary to go into a full review, rather, adjust existing reference values and document how it was done. For new values, a full review is required.
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A HARMONIZED PROCESS FOR NRV DEVELOPMENT 43 Authoritative body or expert panel identifies nutrient for review Accept, revise existing Convene expert or conduct new nutrient review panel systematic review Evaluate existing NRVs Option to keep Option to establish and update or new NRVs adapt NRV Describe the nutrient Define approach and outcomes selected and approach used Dose–response Factorial assessment approach Describe the evidence base Appraise the evidence Evaluate usual intakes and dietary patterns Evaluate usual intakes and dietary patterns Document adjustments to Assess local local context context Accept, revise, or derive FIGURE 3-1 Flow diagram for deriving nutrient reference values. NOTE: NRV = nutrient reference value.
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a rationale and description of why a nutrient review was warranted, and how it would address a current public health concern, and (2) a documented literature search demonstrating new, relevant literature since the last nutrient DRI review.
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Conclusions and Recommendation to Support the Process for Convening a Review of Nutrient Reference Values The committee came to the following conclusions: Two international organizations, WHO and FAO, both with mis sions to facilitate global cooperation in nutrition and health mat ters, present an opportunity for enabling harmonization of the process for deriving NRVs on a global scale by serving as a con vener of an expert review panel. Convening a global expert panel would be ideal for promoting a harmonized process and making efficient use of the available resources.
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, or the International Union of Nutritional Sciences (IUNS) , or secondarily, a regional consortium, should convene an expert panel to identify relevant outcome measures and request a systematic review for the nutrient of interest, and appoint a panel to advise on how to adapt the values to different population subgroups and settings.
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Yet, it is a necessary process for managing the scope, time, and expense of a systematic review. As stated in Chapter 2 (see Figure 2-2)
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Assess Uncertainty in the Evidence: Appraisal of Risk of Bias in Individual Studies Evaluation of risk of bias is an inherent step in the systematic review process. As stated in Chapter 2, an evaluation of risk of bias requires assessment of both the internal and external validity of each individual study (Higgins et al., 2011)
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Assessing Uncertainties in the Systematic Review Process One of the main shortcomings of systematic reviews is the heterogeneity that results from pooling studies carried out with different types of evidence, such as animal versus human data or study designs, different population subgroups, exposure doses, administration routes, or levels of compliance. Because such heterogeneity ultimately translates into uncertainty (Hill, 1965)
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1020. evidence for adverse health effects of a nutrient that forms the basis for deriving a UL relies to a high degree on observational studies on humans.
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In such cases, the methods discussed previously for quantitatively adjusting for bias could be applied. Convene an Expert Panel to Evaluate the Evidence After selecting a nutrient for review and initiating a systematic review, an expert nutrient review panel is convened and given its charge.
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BOX 3-2 Steps That Guide Decision Making by a Nutrient Review Panel When Updating or Adapting Existing NRVs • Describe the basis for each nutrition reference value set. o onsider the nutrient and outcomes used/selected in each review, and C the approach used.
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o Appraise the evidence from the systematic review: § Draw conclusions about the NRV. § Document the process, including methods, assumptions, and fac tors that could limit generalizability of the reference value or would require consideration for adaptation (e.g., reference body weight, genetics, environmental conditions)
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When multiple intake–response studies have been identified from a systematic review, several different modeling approaches are possible. One of these is the multivariate dose–response meta-analysis (Crippa and Orsini, 2016)
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. These include assessing the effect of heterogeneity using sensitivity scenario analysis, considering use of moderator variables to adjust intake–response relationships, average models, and estimating confidence intervals for reference values.
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Protein ARs are estimated from nitrogen balance studies by examining the effects of increasingly concentrated intakes that just replaces the amount lost; this level is considered to be the nitrogen and, therefore, protein requirement because the average nitrogen content of protein is 16 percent. Combining Approaches with Other Data to Reduce Chronic Disease Risk Observational epidemiological studies can be used to determine whether usual intakes are in agreement with values obtained through any of these three approaches.
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. Establishing a New Nutrient Reference Value: Appraise the Evidence The next step to deriving a new NRV, as illustrated in the flow diagram in Figure 3-1, is to synthesize and integrate the evidence while accounting for sources of uncertainty.
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Considerations around interindividual variability with important implications for deriving NRVs include the fact that the distribution of biological endpoints is rarely normal; therefore, using the traditional approach of adding two standard deviations to the mean value of requirement is not always the most appropriate. In addition, the magnitude of the variability is frequently unknown, which is the case when NRVs are derived using a systematic review and the data are available only in an aggregated form.
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. Evaluating Usual Intake Levels After describing the existing evidence base, when updating or adapting an existing NRV, or appraising the evidence, when establishing a new NRV, the next step in developing an NRV is to evaluate usual intakes.
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A composite of scaling methods to extrapolate from reference values of one age group to another is provided in Appendix E One method for extrapolation assumes that the physiologic requirement or the upper intake level is proportional to body mass; for example, adult requirements are often adjusted downward for children.
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. Findings, Conclusions, and Recommendations The flow diagram in Figure 3-1 is based on availability of several new tools and methodologies that were either not available or not used in previous nutrient reviews.
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If values are not relevant locally, an expert panel should adapt values to the local context or modify existing values from other experts. OTHER UNCERTAINTIES TO CONSIDER WHEN ESTIMATING A UL In addition to the different types of uncertainty discussed earlier in this chapter, another type of uncertainty in estimating NRVs arises from the use of competing risk–benefit analyses when evaluating ULs based on chronic disease risk-related outcomes versus toxicity-related outcomes.
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assessment of intakes outside the reference values, and (4) characterization of risks associated with excess intake.
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with increasing nutrient intake levels (x-axis)
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prevention of chronic diseases is taken into consideration concurrently with the avoidance of adverse effects. A FRAMEWORK FOR DERIVING NUTRIENT REFERENCE VALUES Based on its review of the strengths and weaknesses in available methodologies, as detailed throughout this chapter, the committee developed a new framework for harmonizing the process for deriving NRVs.
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Findings on the Process of Setting Nutrient Reference Values General principles for setting NRVs are summarized in Box 3-4. Included in Box 3-4, and as emphasized earlier in this chapter, it is critical that all steps in the decision-making process are documented and transparent.
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; • parameters of the search strategy for a systematic review; • confounders or modifiers affecting intake–response in determining a causal relationship; and • competing analyses of different outcomes, such as deficiency versus chronic disease. The committee came to the following conclusion: Identifying a strategy for managing uncertainties is critical to main taining the accuracy and relevance of all NRVs as well as assuring BOX 3-4 General Principles for Setting Nutrient Reference Values (NRVs)
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Such credibility requires the establishment of a transparent process including how members of the review panels are selected and the training and expertise of each; public availability of all material reviewed by the committee during its deliberations; and written protocols for systematic reviews, quality assessment of each study, assumptions made, and evidence synthesis leading up to the established refer ence values.
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, to achieve transparency the nutrient review expert panel should clearly report the reference population, adjust ment factors, and the methodology used. Expert panels should also document the uncertainty in the evidence and in the methods used to develop the NRVs quantitatively.
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2013 EURRECA-estimating vitamin D requirements for deriving dietary reference values. Critical Review of Food Sciemce and Nutrition 53: 1097-1109.
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2017. Guiding prin ciples for developing Dietary Reference Intakes based on chronic disease.
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2016. ROBIS: A new tool to assess risk of bias in systematic reviews was developed.
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