Scientific Report of the 2015 Dietary Guidelines Advisory Committee

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Part D. Chapter 6: Cross-Cutting Topics of Public Health Importance - Continued

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Sodium

Introduction

From its first edition in 1980, the Dietary Guidelines for Americans consistently recommended the public reduce dietary sodium intakes in order to prevent and treat hypertension, CVD, and stroke. This recommendation is based on evidence supporting a dose-dependent relationship between sodium intake and blood pressure and observational data identifying associations between sodium intake and blood pressure and cardiovascular outcomes. However, despite many years of accumulating evidence and public health guidelines focused on changing individual behavior to achieve a reduced sodium intake among Americans, consumption continues to far exceed recommendations. The DGAC has identified dietary sodium as a nutrient of public health concern because of overconsumption, with usual intakes for those ages 2 years and older at 3,463 mg/day.8 Sodium is ubiquitous in the current U.S. food supply and multiple food categories contribute to excessive sodium intake (see Part D. Chapter 1: Food and Nutrient Intakes, and Health: Current Status and Trends, Figure D1.35).

Currently, 30 percent of U.S. adults have high blood pressure (see Part D. Chapter 1: Food and Nutrient Intakes, and Health: Current Status and Trends). Furthermore, the estimated lifetime risk of developing hypertension in the U.S. is 90%. The rate of borderline high blood pressure (defined as a systolic or diastolic blood pressure ≥90th percentile but <95th percentile or blood pressure levels ≥120/80 mm Hg) in youth ages 8 to 17 years is highest in those who are obese (16.2 percent), slightly lower in those who are overweight (11 percent); and this condition is present even in those who are normal weight (5 percent). Dietary sodium reduction can effectively prevent and reduce high blood pressure.9-11 Given the long-standing awareness of this health concern and scientific foundation for dietary treatment, the DGAC conducted a focused review of dietary sodium and its relationship with blood pressure as well as its relationship with CVD.

Question 1: What is the relationship between sodium intake and blood pressure in adults?

Source of evidence: Existing reports

Conclusions

The DGAC concurs with the three conclusions from the 2013 AHA/ACC Lifestyle Guideline that apply to adults who would benefit from blood pressure lowering.

The DGAC concurs that adults who would benefit from blood pressure lowering should “lower sodium intake.” AHA/ACC Grade: Strong; DGAC Grade: Strong

The DGAC concurs that adults who would benefit from blood pressure lowering should “Consume no more than 2,400 mg of sodium/day.” The report also indicates that “Further reduction of sodium intake to 1,500 mg/d can result in even greater reduction in blood pressure”; and concludes that “Even without achieving these goals, reducing sodium intake by at least 1,000 mg/d lowers blood pressure.” AHA/ACC Grade: Moderate; DGAC Grade: Moderate

The DGAC concurs that adults who would benefit from blood pressure lowering should “Combine the DASH dietary pattern with lower sodium intake.” AHA/ACC Grade: Strong; DGAC Grade: Strong

Review of the Evidence

The 2013 AHA/ACC Lifestyle Guideline and associated NHLBI Lifestyle Report summarized strong and consistent evidence that supports dietary sodium reduction as a means to prevent and treat high blood pressure. The studies used to inform the conclusion to lower sodium intake were conducted in older and younger adults, individuals with prehypertension and hypertension, men and women, and African American and non-African American adults. The trials also documented positive effects of sodium reduction that were independent of weight change; and include behavioral interventions where individuals were counseled to reduce sodium, as well as feeding studies.

The recommendation to combine the DASH dietary pattern with lower sodium is based heavily on the results of the DASH sodium trial, which showed clinically significant lowering of blood pressure with sodium intake of 2,400 mg/day and even lower blood pressure with sodium intake of 1,500 mg/day. The goal of 2,400 or less mg/day was selected because it is the estimated average urinary sodium excretion in the DASH sodium trial.

The recommendation to reduce sodium intake by 1,000 mg/day even if goals for 2,400 mg/day or 1,500 mg/day cannot be reached comes from studies where this level of sodium reduction was beneficial for blood pressure lowering.

The differences in the evidence grade for the three conclusions related to sodium and blood pressure in adults results from the differences in the number and power of clinical trials supporting each recommendation. For example, a grade of “moderate” was assigned to the second conclusion because fewer clinical trials informed the goals of 2,400 and 1,500 mg/day than for the overall goal of sodium reduction.

For additional details on this body of evidence, visit: References 1, 2, 4 and 9 and Appendix E-2.42

Question 2: What is the relationship between sodium intake and blood pressure in children?

Source of evidence: Existing systematic review with a NEL systematic review update

Conclusions

The 2015 DGAC concurs with the 2010 DGAC that “a moderate body of evidence has documented that as sodium intake decreases, so does blood pressure in children, birth to age 18 years.” DGAC Grade: Moderate

Review of the Evidence

The 2010 DGAC conducted a systematic review to examine the relationship between sodium intake and blood pressure in children from birth to age 18 years, examining studies published from January 1970 to May 2009. That systematic review included 19 articles from 15 intervention studies and four prospective cohort studies.

The 2015 DGAC updated this systematic review and identified two additional articles published since May 2009, including one RCT and one prospective cohort study.12, 13

The 2015 DGAC considered the evidence reviewed by the 2010 DGAC related to dietary sodium intake and blood pressure in children, and determined that, based on the two new studies identified in the updated search, changes were not warranted to the conclusion statement or grade. In aggregate, the data reviewed by the 2010 DGAC indicated that sodium reduction modestly lowers BP in infants and children. Neither of the two studies identified in the update found a relationship between dietary sodium intake and blood pressure in healthy, normotensive children.

For additional details on this body of evidence, visit: http://NEL.gov/conclusion.cfm?conclusion_statement_id=250452

Question 3: What is the relationship between sodium intake and cardiovascular disease outcomes?

Source of evidence: Existing report with a NEL systematic review update

Conclusions

The DGAC concurs with the IOM Report: Sodium Intake in Populations, which concluded that “although the reviewed evidence on associations between sodium intake and direct health outcomes has methodological flaws and limitations, when considered collectively, it indicates a positive relationship between higher levels of sodium intake and risk of CVD. This evidence is consistent with existing evidence on blood pressure as a surrogate indicator of CVD risk.” IOM Grade: Grade not determined, outside the statement of task; DGAC Grade: Moderate

The DGAC concurs with the IOM Report: Sodium Intake in Populations that “evidence from studies on direct health outcomes is inconsistent and insufficient to conclude that lowering sodium intakes below 2,300 mg/day either increases or decreases risk of CVD outcomes (including stroke and CVD mortality) or all-cause mortality in the general U.S. population.” IOM Grade: Grade not determined, outside the statement of task; DGAC Grade: Grade not assignable

The DGAC concurs with the NHLBI Lifestyle Report, which concluded that “a reduction in sodium intake by approximately 1,000 mg/day reduces CVD events by about 30 percent” and that “higher dietary sodium intake is associated with a greater risk for fatal and nonfatal stroke and CVD.” NHLBI Strength of Evidence: Low; DGAC Grade: Limited 

The DGAC concurs with the NHLBI Lifestyle Report that “evidence is not sufficient to determine the association between sodium intake and the development of heart failure.” NHLBI Strength of Evidence: Not assigned due to insufficient evidence; DGAC Grade: Grade not Assignable

Review of the Evidence

The DGAC updated systematic reviews done in 2013 by the IOM4 and NHLBI,1 and identified four additional articles published since 2013, all of which were prospective cohort studies.14-17

Of note, the evidence reviewed for the 2013 IOM report was published between 2003 and December 2012. The DGAC concluded that the reviewed evidence on associations between sodium intake and direct health outcomes has methodological flaws and limitations. Specifically, the Committee documented the small number of well-conducted studies evaluating sodium intake and direct health outcomes; the inconsistency in findings across the published literature, possibly due to methodological factors; the lack of comparability in sodium intake levels across studies particularity in international studies; and the absence of strong data related to sodium goals and direct health outcomes, not including hypertension.

The DGAC considered the conclusions reached by the IOM and NHLBI related to dietary sodium intake and risk of CVD, and determined that the findings from the four new studies identified in the updated search did not warrant changes to the conclusion statements. In aggregate, the data indicate a relationship between higher sodium intake and higher risk of CVD.

For additional details on this body of evidence, visit: http://NEL.gov/conclusion.cfm?conclusion_statement_id=250457

Question 4: What effect does the interrelationship of sodium and potassium have on blood pressure and cardiovascular disease outcomes?

Source of evidence: Existing report

Conclusions

The DGAC concurs with the NHLBI Lifestyle Report that: “Evidence is not sufficient to determine whether increasing dietary potassium intake lowers blood pressure.” NHLBI Strength of Evidence: Not assigned due to insufficient evidence; DGAC Grade: Not Assignable

The DGAC concurs with the NHLBI Lifestyle Report that: “In observational studies with appropriate adjustments (e.g., blood pressure, sodium intake), higher dietary potassium intake is associated with lower risk for stroke.” NHLBI Strength of Evidence:  Low; DGAC Grade: Limited

The DGAC concurs with the NHLBI Lifestyle Report that: “Evidence is not sufficient to determine an association between dietary potassium intake and coronary heart disease (CHD), heart failure, and cardiovascular mortality.” NHLBI Strength of Evidence:  Not assigned due to insufficient evidence; DGAC Grade: Grade not Assignable

Review of the Evidence

The NHLBI Lifestyle Report summarized limited evidence on the relationship between potassium intake and blood pressure, CHD, heart failure, cardiovascular mortality, or stroke. Although it is postulated that a high ratio of sodium intake to potassium intake is a stronger risk factor for hypertension than either factor alone, the evidence base to support this hypothesis is insufficient for drawing definitive conclusions. Although results of epidemiologic studies suggest that potassium consumption influences the risk of CVD, the strength of the evidence is insufficient to draw conclusions about CHD, heart failure, or cardiovascular mortality. The evidence is limited with regard to stroke, coming from studies with weaker designs in which investigators were able to make appropriate statistical adjustments for potential confounders of the relationship.

For additional details on this body of evidence, visit: References 1 and 2

Implications

The current average sodium intake in the United States is 3,478 mg/d, far exceeding recommendations. Given the well-documented relationship between sodium intake and high blood pressure, sodium intake should be reduced and combined with a healthful dietary pattern (as described in Part D. Chapter 2: Dietary Patterns, Foods and Nutrients, and Health Outcomes).

The general population, ages 2 years and older, should rely on the recommendations of the IOM Panel on Dietary Reference Intakes for Electrolytes and Water.9 A tolerable upper limit was set by the Panel at 2,300 mg/day based on evidence showing associations between high sodium intake, high blood pressure, and subsequent risk of heart disease, stroke, and mortality. Of note, the AHA/ACC recommendation of less than 2,400 mg/day (see conclusions for sodium question 1) is slightly different than the less than 2,300 mg/day recommended by the IOM Panel on Dietary Reference Intakes or the 2010 Dietary Guidelines for Americans; less than 2,400 mg/day was selected because it was the estimated average urinary sodium excretion in the DASH-sodium trial.

Individuals who would benefit from blood pressure lowering (i.e., those with prehypertension or hypertension), should rely on the recommendations in the 2013 AHA/ACC Lifestyle Guideline. These include: lowering sodium intake in general; or consuming no more than 2,400 mg of sodium/day; or lowering sodium intake to 1,500 mg per day for even greater reduction in blood pressure; or lowering sodium intake by at least 1,000 mg per day even if the goals of 2,400 or 1,500 mg per day cannot be met.

For decades, sodium intake in the United States has exceeded recommendations in spite of numerous national campaigns, through programs such as the NHLBI’s National High Blood Pressure Education Program and the CDC’s State Heart Disease and Stroke Prevention Program, focused on individual behavior change for sodium reduction. As described in Part D. Chapter 1: Food and Nutrient Intakes, and Health: Current Status and Trends, sodium is ubiquitous in the U.S. food supply and almost all food categories contribute to intake levels. This unique feature of sodium makes it difficult for individuals to achieve recommended intake. As such, we recommend that a primary emphasis be placed on policies and population-based strategies for sodium reduction while at the same time paying attention to consumer education. Local, state, and Federal agencies should consider a comprehensive and coordinated strategy, that includes partnerships with the food industry, to reduce the sodium content of foods in the United States based on the socio-ecological model highlighted in the 2015 DGAC’s conceptual model (see Part B. Chapter 1: Introduction).

These strategies should be consistent with the recommendation described in the 2010 IOM report on Strategies to Reduce Sodium Intake in the United States.5 The primary strategy that was recommended is that “The FDA should expeditiously initiate a process to set mandatory national standards for the sodium content of foods”. This would include: 1) “a modification of the generally recognized as safe (GRAS) status of salt added to processed foods in order to reduce the salt content of the food supply in a stepwise manner”; 2) “FDA should likewise extend its stepwise application of the GRAS modification, adjusted as necessary, to encompass salt added to menu items offered by restaurant/foodservice operations that are sufficiently standardized so as to allow practical implementation”; and 3) “FDA should revisit the GRAS status of other sodium-containing compounds as well as any food additive provisions for such compounds and make adjustments as appropriate, consistent with changes for salt in processed foods and restaurant/foodservice menu items.”

Population sodium reductions efforts should consider: 1) the varied technical and functional roles that sodium plays in foods and the complexity of reducing sodium in foods; 2) the recent accomplishments and voluntary reduction efforts by the food industry; and 3) consumer demand for lower-sodium products. More information about strategies for reducing sodium intake in the United States can be found in the IOM report, at http://www.iom.edu/Reports/2010/Strategies-to-Reduce-Sodium-Intake-in-the-United-States.aspx.

Informative food labels should be used to effectively promote awareness of sodium content in foods. Consumers would benefit from a standardized, easily understood front-of-package (FOP) label on all food and beverage products to give clear guidance about a food’s healthfulness. An example is the FOP label recommended by the IOM,18 which included calories, and 0 to 3 “nutritional” points for added sugars, saturated fat, and sodium. This would be integrated with the Nutrition Facts Panel, allowing consumers to quickly and easily identify nutrients of concern for over-consumption, in order to make healthier choices.

Public-private-community partnerships should be created to reduce sodium levels in commercially processed and restaurant foods.

Strategies that complement policies and support consumers to make dietary behavior changes also are needed. These include (but are not limited to): 1) nutrition services and comprehensive lifestyle interventions by multidisciplinary teams;2 2) widely available diet planning tools that include sodium as an area of focus; and 3) educational programs that teach adults simple recipes that emphasize flavoring unsalted foods with spices and herbs.

Although the evidence on potassium and blood pressure is limited, the DGAC recognizes potassium as a nutrient of concern (see Part D. Chapter 1: Food and Nutrient Intakes, and Health: Current Status and Trends) and encourages increased potassium intake through potassium-rich foods such as vegetables and fruits (see Table D1.7).

Interventions, preferably nonpharmacologic, are needed for children because borderline high blood pressure occurs concomitantly with overweight, obesity, and other cardio-metabolic risk factors (see Part D. Chapter 1: Food and Nutrient Intakes, and Health: Current Status and Trends). Evidence-based strategies in clinical and public health settings need to be implemented and complemented by environmental approaches to reverse these high priority health problems in children.

For blood pressure lowering and hypertension prevention, action is needed at both the individual and population levels.

Sodium reduction in youth will require changes in their food environments and school and community-based education on healthful eating.

School systems should adopt mandatory age-appropriate nutrition and physical activity curricula (K-12) that incorporate the core principles of the future 2015 Dietary Guidelines.

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