Guiding Principles for Developing Dietary Reference Intakes Based on Chronic Disease (2017) / Chapter Skim
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3 Conceptual and Methodological Challenges in Establishing Chronic Disease Dietary Reference Intakes
3 Conceptual and Methodological Challenges in Establishing Chronic Disease Dietary Reference Intakes
Pages 73-88
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From page 73... ...
Systematic reviews in nutrition have many special challenges not present in reviews of pharmacologic agents, even without adding the complexity of chronic disease endpoints. As discussed in this chapter, NOFS-chronic disease questions raise spe 73
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From page 74... ...
These factors include • Characterizations of nutrient intake or exposures of individuals, • Ways to account for intra- or inter-personal biological variations in effects of nutrient exposure, • Nutrient interrelationships, • Subpopulation differences in effects of a given nutrient intake, • Study designs available for making causal judgments, and • Intra- and inter-person variability in measures of exposure and outcome. The nature of the challenges relates in part to the level at which diet or nutrition is being considered.
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From page 75... ...
CHARACTERIZING NUTRIENT INTAKES (EXPOSURES) Documenting what people eat to the greatest possible degree of certainty is fundamental for assessing NOFS-chronic disease relationships because the relationships themselves carry an inherent measure of uncertainty.
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From page 76... ...
ACCOUNTING FOR BIOLOGICAL FACTORS THAT INFLUENCE NUTRIENT EXPOSURES Nutrient intakes, even when assessed with minimal error, may not necessarily reflect the biological exposures that influence chronic disease pathways. As indicated above, the biological "dose" associated with a given amount of food is affected by the chemical form of the nutrient and its digestibility and bioavailability in the human gastrointestinal tract.
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From page 77... ...
ASSESSING BIASES DUE TO STUDY DESIGNS Basing judgments about causal relationships using the typical biomedical hierarchy of study designs inherently lessens the ability to make definitive judgments about NOFS-chronic disease questions because the relevant evidence is much more likely to rely on observational study designs, rather than RCTs. RCTs are at the top of the hierarchy (i.e., are the strongest study designs)
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From page 78... ...
C↓ Plant sterols and stanols P↓ α-Linolenic acid P↓ Oleic acid P↓ Stearic acid P-NR Nuts (unsalted) P↓ Carbohydrate High intake of NSP (dietary fiber)
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From page 79... ...
b Evidence also summarized for selected specific fatty acids; see myristic and palmitic acid. c For dental caries.
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From page 80... ...
Residual confounding due to lack of proper statistical adjustments, untestable assumptions, or measurement error limits the causal certainty, even with the best observational study design and execution. However, RCT designs have limitations for answering NOFS-chronic disease questions, and observational data are indispensable for certain aspects of the process of developing DRIs, including chronic disease DRIs.
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From page 81... ...
The inherent susceptibility of dietary assessments to systematic error also affects the certainty of evidence from observational studies; unlike trials, in which the intervention is the basis for the comparison, the classification on usual dietary intake is the basis for the comparison in observational studies (see Chapter 4)
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From page 82... ...
NOTES: BMC = bone mineral content; BMD = bone mineral density; BMI = body mass index; CVD = cardiovascular disease.
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From page 83... ...
The general challenges in evaluating NOFS-chronic disease relationships for DRI purposes are in the first column, with comments in BOX 3-1 Key Questions Guiding the Evidence Review for the Calcium/Vitamin D Update Key Question 1. What is the effect of vitamin D, calcium, or combined vita min D and calcium intakes on clinical outcomes, including growth, cardiovas cular diseases, body weight outcomes, cancer, immune function, pregnancy or birth outcomes, mortality, fracture, renal outcomes, and soft tissue calcification?
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From page 84... ...
D concentrations reduces the intake-response uncertainty that would be associated with using self relationships reported intake data, but DRIs based on serum levels require translation of serum levels into recommendations for dietary intake from food and/or supplements, and consideration of the possibility that the vitamin D in supplements has different levels of biological activity compared to food sources.
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From page 85... ...
Multiple potential Evidence review questions related to health effects of clinical outcomes vitamin D address effects of vitamin D intake or serum and surrogates 25(OH) D concentrations on growth, cardiovascular diseases, body weight outcomes, cancer, immune function, pregnancy or birth outcomes, mortality, fracture, renal outcomes, soft tissue calcification or on surrogate markers such as hypertension, blood pressure, and bone mineral density, and hypercalcemia; potential adverse effects of sunlight (as a "source" of vitamin D)
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From page 86... ...
Criteria for inclusion Primary studies eligible for inclusion in the systematic in systematic review review were "randomized controlled trials (RCTs) , non-randomized, prospective comparative studies of interventions; prospective, longitudinal, observational studies (where the measure of exposure occurred before the outcome)
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From page 87... ...
. The final chapter of the report addresses questions considered by the committee about the nature of the process to be used when developing chronic disease DRIs in relation to the existing DRI process, as described in Chapter 2.
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From page 88... ...
2009. Opportunities and challenges in conducting systematic reviews to support the development of nutrient reference values: Vitamin A as an example.
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