SODIUM INTAKE
                        IN POPULATIONS

ASSESSMENT OF EVIDENCE

Committee on the Consequences of Sodium Reduction in Populations

Food and Nutrition Board

Board on Population Health and Public Health Practice

Brian L. Strom, Ann L. Yaktine, and Maria Oria, Editors

INSTITUTE OF MEDICINE

       OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

Washington, D.C.

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SODIUM INTAKE IN POPULATIONS ASSESSMENT OF EVIDENCE Committee on the Consequences of Sodium Reduction in Populations Food and Nutrition Board Board on Population Health and Public Health Practice Brian L. Strom, Ann L. Yaktine, and Maria Oria, Editors

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THE NATIONAL ACADEMIES PRESS  500 Fifth Street, NW  Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Govern- ing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineer- ing, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropri- ate balance. This study was supported by Contract/Grant No. 200-2011-38807 between the National Academy of Sciences and the Centers for Disease Control and Preven- tion. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project. International Standard Book Number-13:  978-0-309-28295-6 International Standard Book Number-10:  0-309-28295-0 Additional copies of this report are available for sale from the National Academies Press, 500 Fifth Street, NW, Keck 360, Washington, DC 20001; (800) 624-6242 or (202) 334-3313; http://www.nap.edu. For more information about the Institute of Medicine, visit the IOM home page at: www.iom.edu. Copyright 2013 by the National Academy of Sciences. All rights reserved. Printed in the United States of America The serpent has been a symbol of long life, healing, and knowledge among almost all cultures and religions since the beginning of recorded history. The serpent adopted as a logotype by the Institute of Medicine is a relief carving from ancient Greece, now held by the Staatliche Museen in Berlin. Suggested citation: IOM (Institute of Medicine). 2013. Sodium intake in popula- tions: Assessment of evidence. Washington, DC: The National Academies Press.

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“Knowing is not enough; we must apply. Willing is not enough; we must do.” —Goethe Advising the Nation. Improving Health.

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Acad- emy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding e ­ ngineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineer- ing programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. C. D. Mote, Jr., is presi- dent of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Insti- tute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sci- ences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. C. D. Mote, Jr., are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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COMMITTEE ON THE CONSEQUENCES OF SODIUM REDUCTION IN POPULATIONS BRIAN L. STROM (Chair), George S. Pepper Professor of Public Health, University of Pennsylvania School of Medicine, Philadelphia CHERYL A. M. ANDERSON, Associate Professor of Family and Preventive Medicine, University of California, San Diego JAMY ARD, Associate Professor of Epidemiology and Prevention, Wake Forest Baptist Health, Winston-Salem, North Carolina KIRSTEN BIBBINS-DOMINGO, Associate Professor of Medicine and of Epidemiology and Biostatistics, University of California, San Francisco, and Co-Director, San Francisco General Hospital, California NANCY R. COOK, Professor in the Department of Medicine at Harvard Medical School and Brigham & Women’s Hospital, Boston, Massachusetts MARY KAY FOX, Senior Researcher, Mathematica Policy Research, Inc., Cambridge, Massachusetts NIELS GRAUDAL, Senior Consultant, Copenhagen University Hospital, Rigshospitalet, Denmark JIANG HE, Joseph S. Copes Professor of Epidemiology, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana JOACHIM IX, Associate Professor of Medicine, Veterans Affairs San Diego Healthcare System, California STEPHEN E. KIMMEL, Professor of Medicine and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia ALICE H. LICHTENSTEIN, Gershoff Professor of Nutrition Science and Policy, Tufts University, Boston, Massachusetts MYRON WEINBERGER, Professor Emeritus of Medicine, Indiana University School of Medicine, Indianapolis and Editor-in-Chief, Journal of the American Society of Hypertension IOM Staff MARIA ORIA, Study Director ANN L. YAKTINE, Study Director JULIA HOGLUND, Research Associate COLIN F. FINK, Senior Program Assistant ANTON BANDY, Financial Officer GERALDINE KENNEDO, Administrative Assistant LINDA D. MEYERS, Director, Food and Nutrition Board ROSE MARIE MARTINEZ, Director, Board on Population Health and Public Health Practices v

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Reviewers This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report: MICHAEL H. ALDERMAN, Albert Einstein College of Medicine DAVID B. ALLISON, University of Alabama, Birmingham LAWRENCE J. APPEL, Johns Hopkins University GLENN M. CHERTOW, Stanford University School of Medicine JOHANNA T. DWYER, Tufts Medical Center SHIRIKI K. KUMANYIKA, University of Pennsylvania Perelman School of Medicine JOSEPH LAU, Brown University DAVID A. McCARRON, University of California, Davis SUZANNE P. MURPHY, University of Hawaii, Manoa SUZANNE OPARIL, University of Alabama, Birmingham DONALD B. RUBIN, Harvard University ANNA MARIA SIEGA-RIZ, University of North Carolina at Chapel Hill JUDITH S. STERN, University of California, Davis vii

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viii REVIEWERS Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by LYNN R. GOLDMAN, George Washington University, and SUSAN J. CURRY, University of Iowa. Appointed by the National Research Council and the Institute of Medicine, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

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Preface Heart disease and stroke are major cardiovascular diseases (CVDs) and leading causes of death for both men and women in the United States. Major risk factors of CVD, such as high blood pressure, high levels of low- density lipoprotein cholesterol, and smoking, are frequently found among the U.S. population. Other factors, however, such as a poor diet, also can contribute to high blood pressure and disease risk. For more than four decades, controversies have surrounded the contribution of sodium con- sumption as a risk factor for noncommunicable diseases, including CVD. Numerous domestic and international organizations and governments have advised populations against consuming high levels of sodium. Investigators have applied models based on blood pressure decreases to predict the num- ber of deaths that would be saved in the general population from reducing sodium consumption. Although most biomarkers have limitations as indica- tors of risk of adverse health outcomes, the evidence for blood pressure as a surrogate endpoint for risk of CVD and stroke is widely recognized and accepted. Sodium, however, might execute its functions through various processes in addition to blood pressure. Thus, any strategy to reduce the consumption of sodium should include studies that demonstrate an asso- ciation between sodium consumption and direct health effects. Although there is agreement that sodium policies should be guided by research based on direct health outcomes, unfortunately, randomized controlled trials and observational studies that have looked at the association between sodium and direct health outcomes are few and have been interpreted in many ix

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x PREFACE different ways. These differences underscore the difficulties in accurately measuring the long-term health effects of diets or individual nutrients that are consumed in the context of a diet. In 2005, as part of its work on Dietary Reference Intakes, the Institute of Medicine (IOM) conducted a review of the scientific literature on the association between sodium and health effects, including both intermediate and direct health outcomes. Since that time, more data have been collected but the controversies continue and have slowed down the ability to imple- ment sodium policies that are consistent with the current Dietary Guide- lines for Americans. Adding to these longstanding controversies is emerging evidence on potential adverse effects of a too-low dietary sodium intake for some population subgroups. The need for an in-depth examination of the scientific literature became obvious. The Centers for Disease Control and Prevention of the U.S. Department of Health and Human Services asked the IOM to convene an expert committee to examine the designs, meth- odologies, and conclusions of this emerging evidence and to comment on the implications of their findings for population-based sodium-reduction strategies. Of particular interest to the agency was assessing benefits and adverse outcomes of reducing sodium intake in the population and in relevant subgroups that have been described as being particularly at risk. These subgroups are individuals with hypertension and prehypertension, those 51 years of age and older, African Americans, and those with dia- betes, chronic kidney disease, and congestive heart failure. The committee conducted an extensive review of the peer-reviewed literature. A public workshop also was conducted, which provided an opportunity for experts outside the committee to present some of the most controversial data and for stakeholders to describe their positions on relevant issues. The contribu- tions of the workshop speakers and additional information gathered by the committee were invaluable for its deliberations. I am deeply indebted to the committee members who generously gave their time and effort to complete this task in a very short time. Their diver- sity in expertise and backgrounds and in-depth discussions shed light on highly complex scientific issues. In addition, on behalf of the committee, I would like to thank the IOM staff, study co-directors Ann L. Yaktine and Maria Oria, research associate Julia Hoglund, and senior program assistant Colin Fink, who worked tirelessly to complete this task. My gratitude also goes to the Director of the Food and Nutrition Board, Linda D. Meyers, and the Director of the Board on Population Health and Public Health Practices, Rose Marie Martinez, for their guidance and support during the entire study.

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PREFACE xi It is my hope that the conclusions of this committee will add to cur- rent discussions about sodium intake and health and will help future policy makers as they continue to decide and implement sodium strategies that will benefit public health. Brian L. Strom, Chair Committee on the Consequences of   Sodium Reduction in Populations

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Contents SUMMARY 1 1 INTRODUCTION 11 Background, 11 The Committee’s Task, 15 The Study Process, 17 Organization of the Report, 17 References, 18 2 APPROACH TO EVIDENCE REVIEW 21 General Approach of the Committee, 21 Literature Review, 22 Evaluation of Studies, 26 Methodological Issues in Sodium Research: Sodium Intake Assessment, 28 References, 34 3  SODIUM INTAKE AND INTERMEDIATE MARKERS FOR HEALTH OUTCOMES 39 Background, 39 Blood Pressure as a Biomarker for Cardiovascular Disease, 41 Evidence Associating Sodium Intake with Blood Pressure, 43 xiii

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xiv CONTENTS Evidence Associating Sodium Intake with Biomarkers of Progession of Prior Kidney Disease, 49 References, 52 4 SODIUM INTAKE AND HEALTH OUTCOMES 57 Cardiovascular Disease, Stroke, and Mortality, 58 Synthesis of the Evidence, 101 Studies on Kidney Disease, 111 Studies on Metabolic Syndrome, Diabetes, and Gastric Cancer, 112 Additional Health Outcomes, 113 References, 113 5 FINDINGS AND CONCLUSIONS 119 Introduction, 119 Findings and Conclusions, 120 Future Research to Address Gaps in Data and Methodology, 125 References, 126 APPENDIXES A Acronyms and Abbreviations 127 B Committee Member Biographical Sketches 131 C Open Session Agendas 137 D Biomarkers Figure 141 E Literature Search Strategy 143 F Presentation of Results—Evidence Tables 145