Guiding Principles for Developing Dietary Reference Intakes Based on Chronic Disease (2017) / Chapter Skim
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5 Measuring Chronic Disease Outcomes
5 Measuring Chronic Disease Outcomes
Pages 107-128
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From page 107... ...
committees with guidance on considerations related to potential biases and limitations in measuring chronic disease outcomes reported in individual research studies and included in systematic reviews and evidence summaries that are used to make judgments about relationships between NOFSs and a chronic disease. Considerations include how well the outcome has been defined and measured, either directly or indirectly with a surrogate marker that is sufficiently specific to reflect the causal pathway of potential interest.
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From page 108... ...
Research studies often include information on biomarkers along a pathway between exposure and disease, and some can serve as surrogate markers of disease when chronic disease events have not been measured or were observed in numbers too small to permit definitive statistical analyses of causal relationships. CHRONIC DISEASE OUTCOMES Defining Chronic Disease Chronic diseases, including diabetes, cardiovascular and neurodegenerative diseases, and many common cancers, manifest over a lifetime and can begin before birth.
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systematic review (WHO, 2012) that explored the effects of potassium on all cardiovascular disease, stroke, and coronary heart disease events (fatal and non-fatal)
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As an example, coronary heart disease may be suspected based on medical and family history, risk factors, and tests, but no single test for a definitive diagnosis is currently available. Data from studies relying on self-reporting of chronic diseases depend on having had an opportunity for diagnosis as well as accurate recall of the diagnosis; they may, therefore, be regarded as not suitably accurate when establishing DRIs.
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. Using Surrogate Markers as a Substitute for a Chronic Disease Outcomes The initial problem formulation (see Figure 1-2)
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. Without adequate 100 percent (e.g., with Always <100 percent (no intake, proportion of very low intakes of vitamin chronic diseases occur in 100 the population who will C, everyone will develop percent of the population; for develop the deficiency or scurvy, as vitamin C example, the lifetime risk of chronic disease deficiency is the only cause cancer in the United States is of scurvy)
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From page 113... ...
are included in the definition for completeness, the focus here is on biomarkers of disease endpoints. Surrogate Markers in Studies of Nutrient-Chronic Disease Relationships As noted in Chapter 3, studies that employ randomized controlled trial (RCT)
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Surrogate disease marker (also known as a surrogate marker, surrogate end point, or surrogate disease outcome marker) : A biomarker of effect that predicts clinical benefit (or harm, or lack of benefit or harm)
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for prostate cancer or serological markers of inflammation in various infections or rheumatic conditions. Another challenge is the usual modest ability of candidate surrogate markers to predict full disease outcomes.
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. Another example of the challenges is the ongoing need to find surrogate markers for cardiovascular disease, one of the major causes of death worldwide.
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. Qualified Surrogate Markers Biomarkers of effect (in this case, a chronic disease)
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Examples of biomarkers accepted as qualified surrogate endpoints for the purpose of health claims for specific chronic disease endpoints by FDA's Center for Food Safety and Nutrition include (1) serum LDL cholesterol concentration, total serum cholesterol concentration, and blood pressure for cardiovascular disease, (2)
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disease risk in prospective cohort studies Dental Caries Fluoride (AI) Decreased Calcium disease risk Type 2 Diabetes Magnesium, vitamin E, chromium, dietary fiber, vitamin D Immune Responsed Vitamin D Kidney Stones Potassium (AI)
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fracture risk, Bone mineral densityc Pulmonary Disease Vitamin C NOTES: AI = adequate intake; DRI = Dietary Reference Intake; EAR = Estimated Average Requirement; RDA = Recommended Dietary Allowance; UL = Tolerable Upper Intake Level. a In most cases, chronic disease outcomes were not used to set DRIs because the evidence was insufficient and/or inconsistent.
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From page 121... ...
Chronic disease DRIs, however, are desirable but not essential. Therefore, despite the movement toward using surrogate markers in nutritional applications to chronic disease prevention, the committee urges caution in applying them, unless they meet a high bar for being considered qualified (as discussed in the next section)
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. This committee was tasked with recommending and justifying one of these two options related to selecting chronic disease outcomes or biomarkers of effect when reviewing the evidence related to establishing DRIs based on the chronic disease outcome of interest.
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As described in Chapter 3, the evidence base for relationships between NOFSs and chronic disease outcomes includes studies that vary widely in design and health outcome measurement. Observational studies may include direct measurements of chronic disease outcomes in very large populations and over long follow-up periods, but also may include measurements of biomarkers of effect, qualified (i.e., surrogate markers)
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Recognizing that chronic disease outcomes are the ideal measurement, the committee recommends that when a surrogate marker is used as proxy for a chronic disease outcome, the evidence related to its qualification is reviewed and surrogate markers
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DRI committees will need to carefully evaluate the support for surrogacy claims in studies being reviewed. Using nonqualified disease markers or surrogate disease markers qualified for other purposes (e.g., for drug evaluation)
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1992. Statistical validation of intermediate endpoints for chronic diseases.
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2012. Cardiovascular disease risk reduction by raising HDL cholesterol -- Current therapies and future opportunities.
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2012. Effect of increased potassium intake on cardio vascular disease, coronary heart disease and stroke.
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