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Dietary Reference Intakes for Sodium and Potassium (2019)

Chapter: Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"

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Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 435
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 436
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 437
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 438
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 439
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 441
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 442
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 443
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 444
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 445
Suggested Citation:"Appendix C: Committee's Assessment of the "Agency for Healthcare Research and Quality Systematic Review"." National Academies of Sciences, Engineering, and Medicine. 2019. Dietary Reference Intakes for Sodium and Potassium. Washington, DC: The National Academies Press. doi: 10.17226/25353.
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Page 446

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Appendix C Committee’s Assessment of the Agency for Healthcare Research and Quality Systematic Review In accordance with its Statement of Task (see Chapter 1, Box 1-1), the committee was asked to consider the Agency for Healthcare Research and Quality (AHRQ) systematic review, Sodium and Potassium Intake: Effects on Chronic Disease Outcomes and Risks (AHRQ Systematic Review) (­ ewberry et al., 2018), in its derivation of the Dietary Reference Intake N (DRI) values for potassium and sodium. The AHRQ Systematic Review included both the selection of literature and the investigators’ assessment of the strength of evidence for each indicator. Prior to using the AHRQ Systematic Review, the committee assessed its overall quality and methodology. As anticipated in the Guiding Princi- ples for Developing Dietary Reference Intakes Based on Chronic Disease (Guiding Principles Report) (NASEM, 2017), the committee re­ ssessed the a evidence for some relevant indicators in the AHRQ Systematic Review. The details of the additional data analyses conducted by the committee for the purposes of the expanded assessment are included in Chapters 6 and 10. This appendix includes the committee’s approach to reviewing the quality of the AHRQ Systematic Review and to expanding the assessment of the evidence as the fundamental basis for the deliberations regarding establishing Chronic Disease Risk Reduction Intakes for potassium and sodium. 431

432 DIETARY REFERENCE INTAKES FOR SODIUM AND POTASSIUM ASSESSMENT OF OVERALL QUALITY The committee assessed the overall quality of the AHRQ Systematic Review using the AMSTAR 2 tool (Shea et al., 2017).1 The committee determined the AHRQ Systematic Review met the majority of the 16 domains and that it was of overall moderate quality.2 Domains that the AHRQ Systematic Review did not adequately cover related to investigat- ing and explaining the causes of heterogeneity in the results, which in some cases is essential in order to interpret the results of meta-analysis. ASSESSMENT OF METHODOLOGICAL APPROACH As prescribed in the AHRQ guidance, a protocol was prepared and published for the AHRQ Systematic Review used in this study (AHRQ, 2017). The committee reviewed the protocol and determined that the PICO questions3 and the inclusion/exclusion criteria for each indicator included were complete, clear, and appropriate. The committee also reviewed the strength-of-evidence domains and their definitions in the AHRQ guid- ance (AHRQ, 2014) and determined that they were complete, clear, and appropriate. The protocol specified the tools and criteria used for assessing the evidence. The AHRQ guidance scores the body of evidence separately for randomized controlled trials and observational studies and provides guidance for randomized controlled trials. However, the guidance pro- vides flexibility and directs the evidence-based practice centers conduct- ing the systematic review to specify risks of bias specific to the content area. Accordingly, the AHRQ Systematic Review protocol is particularly detailed at describing its constructs and implementation in the risk-of- bias (or study limitations) domain for randomized controlled trials and observational studies separately. Judging risk of bias in an objective and standardized manner is essential to the interpretation and weighing of a study (or a body of evidence) (for explanations of the importance of the risk-of-bias tool, see Chapter 2). In spite of using assessment tools that are objective and formally accepted by the scientific community, the committee recognizes that all assessments regarding determination of risk of bias for individual studies and strength of the evidence for the body of evidence for a specific outcome entail a certain 1  AMSTAR stands for A Measurement Tool to Assess Systematic Reviews. 2  The AMSTAR 2 tool is not intended to result in an overall score. Instead, the tool can be used for a qualitative assessment, where different factors can be weighted differently, depend- ing on the importance or relevance to the research question(s). 3  PICO is a mnemonic device for the important parts of a well-built clinical question. PICO stands for population (or problem or patient), intervention, comparison, and outcome.

APPENDIX C 433 degree of interpretation and judgment. With this in mind, the committee performed two tasks to explore its degree of agreement in the application of these assessment tools with the decisions and judgments of the AHRQ Systematic Review. The committee performed spot checks of the AHRQ Sys- tematic Review’s risk-of-bias assessment and strength-of-evidence rating. The committee understood that it is its prerogative to perform additional analyses and to potentially reach a different strength-of-evidence determination, as long as there is transparency and a scientific basis in its rationale for doing so. Spot Check of the Risk-of-Bias Assessment The committee generally agreed with the risk-of-bias tools criteria for both randomized controlled trials and observational studies, as defined in the AHRQ Systematic Review (for the criteria, see Annex C-1). To check the application of the risk-of-bias criteria, six studies were selected at ran- dom; the selected studies were determined by the AHRQ investigators to have low, moderate, and high level of risk of bias (one of each risk-of-bias level for randomized controlled trials and one of each risk-of-bias level for observational studies). Two members of the committee independently assessed the risk of bias for each study by following the AHRQ risk-of-bias criteria. Discrepancies were minor between the committee members’ and the AHRQ Systematic Review’s risk-of-bias rating for each study. Given previous reports regarding the inconsistent application of the risk-of-bias tools and the large discrepancies in how risk of bias is being evaluated for some specific domains (Jordan et al., 2017), the committee accepted these minor discrepancies as typical and determined that based on this limited spot check, the application of the risk-of-bias tools in the AHRQ Systematic Review was appropriate. Assessing the Application of Strength-of-Evidence Domains The committee conducted a number of checks related to the AHRQ Systematic Review, particularly for outcomes that would likely be relevant for setting DRI values (e.g., blood pressure, cardiovascular disease). In that regard, the committee noted that the conclusions in some relevant recent systematic reviews differ from the conclusions in the AHRQ Sys- tematic Review. For example, the strength of the evidence for an effect of a reduction of sodium intake on reducing blood pressure, an outcome for which a substantial body of evidence exists, was determined as high in past systematic reports (Graudal et al., 2017; NHLBI, 2013; WHO, 2012a). Even if using the same strength-of-evidence domains (e.g., risk of bias, inconsistency, imprecision, and indirectness), the AHRQ Systematic Review rated the strength of evidence as moderate. This discrepancy might

434 DIETARY REFERENCE INTAKES FOR SODIUM AND POTASSIUM give the appearance that the strength of the evidence for the relationship between sodium intake and blood pressure has changed over the past few years. However, the reason for this discrepancy could lie in various other factors, including the strength-of-evidence assessment. To understand this discrepancy, the committee examined salient sys- tematic reviews on sodium and blood pressure and cardiovascular disease outcomes (NHLBI, 2013; WHO, 2012a,b) and an additional systematic review on sodium and blood pressure (Graudal et al., 2017). The commit- tee found a number of differences in the systematic reviews, such as those related to the approach in the literature search, the populations of interest, and various inclusion/exclusion criteria compared to the AHRQ Systematic Review. A major difference that could have led to differences in the final determination, however, was in the application of the inconsistency domain, which refers to the unexplained heterogeneity or variability of study results in a body of evidence, or the imprecision domain. For example, the World Health Organization’s 2012 systematic review concluded that randomized controlled trials on the relationship between sodium intake and blood pressure did not show a serious inconsistency (based on inconsistency in the direction or the size of the effect), which led to a determination of high quality (WHO, 2012a). Conversely, the meta- analysis of the relationship between sodium reduction and systolic and dia- stolic blood pressure conducted by the AHRQ Systematic Review resulted in high inconsistency owing to heterogeneity in the meta-analysis. The AHRQ Systematic Review did not perform further analyses and downgraded the strength of the evidence to moderate based on the existence of inconsistency (for how the AHRQ Systematic Review defined inconsistency, see Box C-1). The committee decided that, in order to understand the nuances and have more clarity in interpreting the evidence, it was essential to explore the sources of heterogeneity in the body of evidence on the relationship between sodium intake and blood pressure. The committee performed sensitivity analyses to investigate sources of heterogeneity. These analyses informed the committee’s assessment of the strength of the evidence for a relationship between sodium intake and systolic and diastolic blood pressure, which it rated as high (for additional details, see Chapter 10). The above example presents one case where analyses beyond those conducted in the AHRQ Systematic Review were helpful in resolving an important question for assessing the evidence for an indicator of inter- est. The committee conducted additional analyses on select results of the AHRQ Systematic Review to clarify its interpretation of the results as needed in order to complete the committee’s task; the additional analyses are described in Chapters 6 and 10.

APPENDIX C 435 BOX C-1 Application of Inconsistency in the AHRQ Systematic Review For randomized controlled trials: The strength of evidence was downgraded based on inconsistency in the direction of effect (beneficial or not) as reported in meta- analysis. Sensitivity analysis was conducted to explore whether the inconsistency (and the heterogeneity, as reflected by the I 2 statistic [a statistic that describes the percent of variation across studies due to heterogeneity]) was caused by study quality or subgroup differences (e.g., hypertensive individuals versus nor- motensives). The heterogeneity seen in meta-analysis could not be explained by inclusion of lower-quality studies. When studies of participants with normal blood pressure were pooled separately from studies of participants with high-normal blood pressure or hypertension to assess the effects of sodium reduction interven- tions on blood pressure, heterogeneity was substantially lower for the pooled anal- yses of normotensives than for the studies of participants with hypertension and for the meta-analyses of all studies. However, inconsistency was still observed in the effect sizes. Thus, the strength of evidence was downgraded for each conclu- sion because of “unexplained heterogeneity.” If the subgroup analyses that were conducted or additional subgroup analyses that were not conducted (e.g., based on different blood pressure methodology, use of antihypertensive medications, or differences in achieved sodium intake) had resulted in consistency across effect sizes as well as significant falls in heterogeneity (as indicated by the I 2 values), the authors would not have downgraded the strength of evidence, as the reasons for the heterogeneity would be explained. Generally, clinical/biological heterogeneity is larger in nutrition trials compared to drug trials. For observational studies: Based on inconsistency on (a) direction of effect (ben- eficial or not) and (b) size of effect (magnitude of change). SOURCE: Personal communication, S. Newberry, RAND Corporation, April 3, 2018. REFERENCES AHRQ (Agency for Healthcare Research and Quality). 2014. Methods guide for effectiveness and comparative effectiveness reviews. Rockville, MD: Agency for Healthcare Research and Quality. AHRQ. 2017. Evidence-based Practice Center systematic review protocol. Project title: Ef- fects of dietary sodium and potassium intake on chronic disease outcomes and related risk factors. https://effectivehealthcare.ahrq.gov/sites/default/files/pdf/sodium-potassium_ research-protocol.pdf (accessed January 17, 2019). Graudal, N. A., T. Hubeck-Graudal, and G. Jurgens. 2017. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride. Cochrane Database of Systematic Reviews 4:CD004022. Jordan, V. M., S. F. Lensen, and C. M. Farquhar. 2017. There were large discrepancies in risk of bias tool judgments when a randomized controlled trial appeared in more than one systematic review. Journal of Clinical Epidemiology 81:72-76.

436 DIETARY REFERENCE INTAKES FOR SODIUM AND POTASSIUM NASEM (National Academies of Sciences, Engineering, and Medicine). 2017. Guiding prin- ciples for developing Dietary Reference Intakes based on chronic disease. Washington, DC: The National Academies Press. Newberry, S. J., M. Chung, C. A. M. Anderson, C. Chen, Z. Fu, A. Tang, N. Zhao, M. Booth, J. Marks, S. Hollands, A. Motala, J. K. Larkin, R. Shanman, and S. Hempel. 2018. Sodium and potassium intake: Effects on chronic disease outcomes and risks. Rockville, MD: Agency for Healthcare Research and Quality. NHLBI (National Heart, Lung, and Blood Institute). 2013. Lifestyle interventions to re- duce cardiovascular risk. Systematic evidence review from the Lifestyle Work Group. https://www.nhlbi.nih.gov/sites/default/files/media/docs/lifestyle.pdf (accessed January 14, 2019). Shea, B. J., B. C. Reeves, G. Wells, M. Thuku, C. Hamel, J. Moran, D. Moher, P. Tugwell, V. Welch, E. Kristjansson, and D. A. Henry. 2017. AMSTAR 2: A critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both. BMJ 358:j4008. WHO (World Health Organization). 2012a. Effect of reduced sodium intake on blood pres- sure, renal function, blood lipids and other potential adverse effects. Geneva, Switzer- land: World Health Organization. WHO. 2012b. Effects of reduced sodium intake on cardiovascular disease, coronary heart disease and stroke. Geneva, Switzerland: World Health Organization.

APPENDIX C 437 ANNEX C-1 RISK OF BIAS CRITERIA USED IN THE AGENCY FOR HEALTHCARE RESEARCH AND QUALITY SYSTEMATIC REVIEW The two sections that follow are the risk-of-bias criteria used in the Agency for Healthcare Research and Quality systematic review, Sodium and Potassium Intake: Effects on Chronic Disease Outcomes and Risks (Newberry et al., 2018). These criteria were developed independent of this committee. RISK OF BIAS ASSESSMENT FOR RANDOMIZED CONTROLLED TRIALS Random Sequence Generation (Selection Bias) For randomized controlled trials, is the sequence generation (recruitment) described as being random? For controlled clinical trials, is the allocation described in such a way that it appears to be free of obvious (intentional) bias? For crossover trials, was the order of receiving treatments randomized adequately? • Low risk: The investigators describe a random component in the sequence generation process such as: referring to a random number table; using a computer random number generator; coin tossing; shuffling cards or envelopes; throwing dice; drawing of lots; mini- mization (minimization may be implemented without a random element, and this is considered to be equivalent to being random). • High risk: The investigators describe a non-random component in the sequence generation process. Usually, the description would involve some systematic, non-random approach; for example, sequence generated by odd or even date of birth; sequence gener- ated by some rule based on date (or day) of admission; sequence generated by some rule based on hospital or clinic record num- ber. Other non-random approaches happen much less frequently than the systematic approaches mentioned above and tend to be obvious. They usually involve judgment or some method of non- random categorization of participants, for example: allocation by judgment of the clinician; allocation by preference of the partici- pant; allocation based on the results of a laboratory test or a series of tests; allocation by availability of the intervention.

438 DIETARY REFERENCE INTAKES FOR SODIUM AND POTASSIUM • Unclear risk: Insufficient information about the sequence genera- tion process to permit judgment of “Low risk” or “High risk.” Allocation Concealment Was the group allocation concealed (such that assignments could not be predicted)? • Low risk: Use of a third party and opaque envelopes or their equiva- lent are low risk. Participants and investigators enrolling partici- pants could not foresee assignment because one of the following, or an equivalent method, was used to conceal allocation: central allo- cation (including telephone, Web-based, and pharmacy-controlled randomization); sequentially numbered drug containers of identical appearance; sequentially numbered, opaque, sealed envelopes. • High risk: Participants or investigators enrolling participants could possibly foresee assignments and thus introduce selection bias, such as allocation based on: using an open random allocation schedule (e.g., a list of random numbers); assignment envelopes were used without appropriate safeguards (e.g., if envelopes were unsealed or nonopaque or not sequentially numbered); alternation or rotation; date of birth; case record number; any other explicitly unconcealed procedure. • Unclear risk: Insufficient information to permit judgment of “Low risk” or “High risk.” This is usually the case if the method of concealment is not described or not described in sufficient detail to allow a definite judgment; for example, if the use of assignment envelopes is described, but it remains unclear whether envelopes were sequentially numbered, opaque and sealed. • Not applicable: Study is a controlled clinical trial. Blinding of Participants and Personnel Were participants and key study personnel blinded to their intervention or exposure status? • Low risk: Any one of the following: no blinding or incomplete blinding, but the review authors judge that the outcome is not likely to be influenced by lack of blinding; blinding of participants and key study personnel ensured, and unlikely that the blinding could have been broken. • High risk: Any one of the following: no blinding of outcome assess- ment, and the outcome is likely to be influenced by lack of blinding;

APPENDIX C 439 blinding of participants and key study personnel attempted, but likely that the blinding could have been broken, and the outcome is likely to be influenced by lack of blinding. • Unclear risk: Any one of the following: insufficient information to permit judgment of “Low risk” or “High risk”; the study did not address this outcome. Just mentioning “placebo” = “unclear.” Blinding of Outcome Assessment • Low risk: Any one of the following: no blinding of outcome assess- ment, but the review authors judge that the outcome measurement is not likely to be influenced by lack of blinding; blinding of out- come assessment ensured, and unlikely that the blinding could have been broken. Apply same criteria as for patients. • High risk: Any one of the following: no blinding of outcome assess- ment, and the outcome measurement is likely to be influenced by lack of blinding; blinding of outcome assessment, but likely that the blinding could have been broken, and the outcome measurement is likely to be influenced by lack of blinding. • Unclear risk: Any one of the following: insufficient information to permit judgment of “Low risk” or “High risk”; the study did not address this outcome; “double blind” and no further information on assessor (e.g., external assessor). Incomplete Outcome Data (Attrition Bias) For randomized controlled trials and clinical controlled trials, could high attrition or uneven attrition across study arms have contributed to bias? For crossover studies, only, was outcome reporting complete for all phases? • Low risk: Similar loss to follow-up across groups OR analyses took loss to follow-up into account (e.g., by intent-to-treat [ITT] analysis, “censoring,” imputing missing data [e.g., by carrying the last observation forward] or qualitatively or quantitatively compar- ing the characteristics of people who dropped out with those who remained in the analysis). • High risk: Differential loss to follow-up across groups with no attempt to take into account or to assess differences between drop- outs and retained participants. • Unclear risk: Nothing mentioned about evaluating impacts or tak- ing into account in analysis.

440 DIETARY REFERENCE INTAKES FOR SODIUM AND POTASSIUM Selective Reporting of Outcome Data For studies that purport to be reporting the prespecified study outcomes, do the outcomes reported match those listed in the Methods section under “Outcomes,” or does the article state that some of the prespecified out- comes will be reported in subsequent articles? • Low risk: Any of the following: the study protocol is available and all of the study’s prespecified (primary and secondary) outcomes that are of interest in the review have been reported in the pre- specified way; the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were prespecified (convincing text of this nature may be uncommon). • High risk: Any one of the following: not all of the study’s pre- specified primary outcomes have been reported; one or more pri- mary outcomes is reported using measurements, analysis methods or subsets of the data (e.g., subscales) that were not prespecified; one or more reported primary outcomes were not prespecified (unless clear justification for their reporting is provided, such as an unexpected adverse effect); one or more outcomes of interest in the review are reported incompletely so that they cannot be entered in a meta-analysis; the study report fails to include results for a key outcome that would be expected to have been reported for such a study. • Unclear risk: Insufficient information to permit judgment of “Low risk” or “High risk.” It is likely that the majority of studies will fall into this category. • Not applicable: Article reports on post-hoc analysis of data from a study initially published elsewhere. Other: Adherence Did the investigators describe rates of adherence to the intervention or some measure of adherence? • Low risk: Adherence was described as high (e.g., based on bio- markers) or as greater than or equal to 80 percent. • High risk: Adherence was described as low. • Unclear risk: Nothing about adherence was mentioned.

APPENDIX C 441 Other: Unequal Distribution Among Groups of Potential Confounders at Baseline Was distribution of demographics (e.g., age, gender, race/ethnicity), comor- bidities, and other potentially critical confounding factors (e.g., blood pres- sure, use of antihypertensives) similar across study arms at baseline (or if not, does the analysis control for baseline characteristics)? • Yes (Low risk): No significant difference between arms in demo- graphic and important comorbidity characteristics (e.g., blood pressure) according to table and/or described by investigators, or difference(s) taken into account in analysis. • No (High risk): Significant difference between arms in age, race, gender, important comorbidity with no attempt to control for the differences. Demonstration That Outcome of Interest Was Not Present at Start of Study for All Participants For example, analysis of the number of people with stroke includes patients that had a stroke before start of study not after the intervention or had a recurring stroke. Note: Incidence versus recurrence. This item is a trigger for excluding individual studies from analyses. Please specify for which outcome this is an issue. • Low risk: No problem. • High risk: People with an outcome of interest were not excluded (specify the outcome, and exclude study for that analysis). Other: Valid Method of Exposure Assessment Was exposure to intervention assessed using a valid method? • Low risk: For sodium or sodium-to-potassium ratio, exposure was assessed with at least one 24-hour urinary analysis with reported quality control measure. For potassium, exposure was assessed using at least one 24-hour urinary analysis with reported quality control measure, chemical analysis of diet or food diary with inter- vention/exposure adherence measure, or composition of potassium supplement with intervention/exposure adherence measure.

442 DIETARY REFERENCE INTAKES FOR SODIUM AND POTASSIUM • High risk: For sodium or sodium-to-potassium ratio or potassium, exposure was assessed with chemical analysis of diet, composition of salt substitute, or food diaries. Exposure was assessed less than 24 hours or through a published food frequency questionnaire. • Moderate risk or unclear: For sodium, 24-hour urinary analysis without reported quality control measure. Chemical analysis of diet without intervention/exposure adherence measure, or com- position of potassium supplement without intervention/exposure adherence measure. For potassium, use of food diaries without quality control. Other: Valid Method of Outcome Assessment Were outcomes assessed using valid methods? • Low risk: Definitions of outcomes are provided by investigators, outcomes are not self-reported, and method of ascertainment is described. • High risk: Definitions are not provided (e.g., for cardiovascular dis- ease morbidity); one or more outcomes is described as self-reported. • Unclear risk: No description of outcome definitions, no mention of method of ascertainment. Other: Valid Statistical Assessment (for Crossover Trials Only) Did the authors report how they did their analysis, and did they do the correct analysis for a crossover (a paired analysis of some type)? • Yes, they report how they analyzed the data, and they report a paired analysis of some type. • No, they report an analysis but it was not paired. • Unclear: They do not report how the analysis was done and the outcomes do not appear to have come from pairing people with themselves. RISK OF BIAS CRITERIA FOR OBSERVATIONAL STUDIES Representativeness of the Exposed Cohort • Low risk: Truly representative of the average named cohort in the community. • High risk: Select group (e.g., only doctors).

APPENDIX C 443 • Moderate risk or unclear: Somewhat representative of average named population or no description of the derivation of the cohort. Selection of the Nonexposed Cohort • Low risk: The recruitment or allocation strategy was similar across exposure groups (drawn from the same community as exposed cohort). • High risk: Drawn from a different source. • Unclear risk: No description. Ascertainment of Sodium and Potassium Exposure (Dietary Assessment/Urinary Assessment) • Low risk of bias: ° Multiple 24-hour urines with reported quality control measures days (more than 4 on average, preferably noncon- secutive) (e.g., instructions given and measure of completeness of collec- tion such as creatinine, urine volume, questionnaire) • Moderate risk of bias: ° Two to measures or correction for regression dilution bias with four 24-hour urine specimens with reported quality control repeated 24-hour urine collection on a sample of participants Multiple days of food diaries ° Multiple nonconsecutive days (more than 4) 24-hour diet recalls ° or food records or correction for regression dilution bias with repeated (nonconsecutive) 24-hour diet recalls for a sample of participants • High risk of bias: ° 24-hour 24-hour urine any reported quality control measures urine without ° Timed-urine collection of less than 24 hours error) A single collection (high random ° Food frequency questionnaire ° Single-day food diaries/records or 24-hour diet recalls ° Spot urine with or without use of a prediction equation for ° estimating 24-hour excretion Potassium Exposure Assessment • Low risk of bias: ° Multiplerecords nonconsecutive days (more than 4) 24-hour diet recalls or food

444 DIETARY REFERENCE INTAKES FOR SODIUM AND POTASSIUM ° Multiple (more than four, preferably nonconsecutive) 24-hour urines with reported quality control measures (e.g., instructions given and measure of completeness of collection, such as creati- nine, urine volume, questionnaire) • Moderate risk of bias: ° Two dilution 24-hour urine specimens or correction for regres- to four sion bias with repeated 24-hour urine collection on a sample of participants ° Two to four nonconsecutive 24-hour with repeated (noncon- recalls/food records or correction for regression dilution bias secutive) 24-hour diet recalls for a sample of participants Food frequency questionnaire validated for potassium intake ° within a subset of the study population against duplicate diets or multiple 24-hour urine collections • High risk of bias: ° Single 24-hourthan one 24-hour urine specimen without any urine specimen Use of more ° reported quality control measures ° Timed-urine collection of less than 24 hours specified above ° Food frequency questionnaire other than that under “Moderate risk of bias” Single-day food records ° Single day of 24-hour recall ° Spot urine specimen(s) with or without use of an equation for ° estimating 24-hour excretion Demonstration That Outcome of Interest Was Not Present at Start of Study for All Participants For example, analysis of the number of people with stroke includes patients that had a stroke before the start of the study, not after the intervention, or had a recurring stroke (incidence versus recurrence). This item is a trig- ger for excluding individual studies from analyses. Please specify for which outcome this is an issue. Comparability Comparability of cohorts on the basis of the design or analysis (Was dis- tribution of health status, demographics, and other critical confounding factors similar across study groups at baseline or did the analysis control for baseline differences between groups?)

APPENDIX C 445 • Low risk: Study provides explanation for and controls for the most important factors likely to affect outcomes, including blood pres- sure for non–blood pressure studies or body mass index. • High risk: Study does not control for blood pressure or other important factors (e.g., demographics). • Moderate risk or unclear: Study does not describe the exact factors controlled for in analysis. Assessment of Outcome Ascertainment of outcome should be appropriate for the type of outcome. • Low risk: The authors describe independent or blind assessment or confirmation of the outcome by reference to secure records (e.g., X-rays, medical records) or use of record linkage (e.g., identifica- tion of outcome through the International Statistical Classification of Diseases and Related Health Problems [ICD] codes on database records). • High risk: Outcomes are described as being self-reported. • Moderate risk or unclear: No description. REFERENCE Newberry, S. J., M. Chung, C. A. M. Anderson, C. Chen, Z. Fu, A. Tang, N. Zhao, M. Booth, J. Marks, S. Hollands, A. Motala, J. K. Larkin, R. Shanman, and S. Hempel. 2018. Sodium and potassium intake: Effects on chronic disease outcomes and risks. Rockville, MD: Agency for Healthcare Research and Quality.

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As essential nutrients, sodium and potassium contribute to the fundamentals of physiology and pathology of human health and disease. In clinical settings, these are two important blood electrolytes, are frequently measured and influence care decisions. Yet, blood electrolyte concentrations are usually not influenced by dietary intake, as kidney and hormone systems carefully regulate blood values.

Over the years, increasing evidence suggests that sodium and potassium intake patterns of children and adults influence long-term population health mostly through complex relationships among dietary intake, blood pressure and cardiovascular health. The public health importance of understanding these relationships, based upon the best available evidence and establishing recommendations to support the development of population clinical practice guidelines and medical care of patients is clear.

This report reviews evidence on the relationship between sodium and potassium intakes and indicators of adequacy, toxicity, and chronic disease. It updates the Dietary Reference Intakes (DRIs) using an expanded DRI model that includes consideration of chronic disease endpoints, and outlines research gaps to address the uncertainties identified in the process of deriving the reference values and evaluating public health implications.

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