February 2018 Issue

Sodium Reduction — How Low Should Clients Go
for Optimal Health?

By Karen Collins, MS, RDN, CDN, FAND
Today's Dietitian
Vol. 20, No. 2, P. 18

Here's an overview of the latest research and the bottom line on how to counsel clients and patients.

Under the latest clinical practice guideline on high blood pressure from the American College of Cardiology (ACC), the American Heart Association (AHA), and nine other organizations, more people than ever before are categorized as having hypertension or elevated blood pressure, and they're advised to limit dietary sodium, ideally to no more than 1,500 mg per day.1

Reducing sodium intake by 1,000 mg per day generally reduces systolic blood pressure by 5 to 6 mm Hg among people with hypertension, and by 2 to 3 mm Hg among normotensive individuals.1 The modest blood pressure reduction in people whose blood pressure is in the normal range is cited to support recommendations to lower sodium intake to help prevent hypertension.

Yet some researchers and health professionals express concern about extreme sodium reduction, based on controversial analyses suggesting that there's a point where aggressive reduction in sodium intake is associated with increased health risk. Other concerns relate to the practicality of promoting dietary sodium at a level currently consumed by less than 5% of US adults rather than a more reachable target.2

Is Lower Better?
Research results are less consistent regarding the benefit of setting a very low sodium target, such as 1,500 mg per day, for greater protection or for particular high-risk groups within the population. But part of that inconsistency is a result of the limitations of the studies involved.

Randomized controlled trials of four weeks or longer demonstrate further reduction in blood pressure with lower sodium, particularly when food is provided to subjects, enhancing adherence to intended sodium intake. For example, in the DASH-Sodium trial, in an overall pattern of food choices typical of the American diet, reducing sodium from 3,500 mg per day to 2,300 mg per day reduced systolic blood pressure by 2.1 mm Hg and diastolic blood pressure by 1.1 mm Hg.3 But a reduction from 3,500 mg per day to 1,150 mg per day decreased systolic blood pressure by 6.7 mm Hg and diastolic blood pressure by 3.5 mm Hg. A Cochrane systematic review of 34 randomized controlled trials concluded that reduction to 3 g per day of salt (equivalent to 1,170 mg per day of sodium) is optimal for an even greater decrease in blood pressure than a more modest reduction (such as 2,300 mg per day).4

Current recommendations from the 2015–2020 Dietary Guidelines for Americans (DGA) and Institute of Medicine (IOM) call for all adults to limit sodium consumption to no more than 2,300 mg per day.5,6 The DGA and the new ACC/AHA guideline recommend a limit of 1,500 mg per day as even more effective for decreasing blood pressure and especially for people with hypertension or elevated blood pressure (referred to as prehypertension in the DGA).1,5

Individual responsiveness to sodium reduction varies, with stronger effects in people who are African American or over age 50, or have hypertension.1,4,7 An earlier American Society of Hypertension position paper called for reducing sodium to 1,500 mg per day particularly for people in these groups, in whom sodium reduction is especially effective in lowering blood pressure, and who are at highest risk of developing high blood pressure.7

Is Lower Risky?
Some published reviews, however, have suggested potential adverse effects of larger decreases in sodium. Reduced sodium intake causes a fall in extracellular volume, which activates the renin-angiotensin-aldosterone system and can lead to increased catecholamine levels.8 However, these compensatory responses are seen especially when sodium intake decreases dramatically over just a few days, yet other analyses show such effects to be minimal in high-quality studies of four weeks or longer.4,9

The other major evidence against maximizing reduction of dietary sodium involves the question of increased disease endpoints, such as cardiovascular events and mortality or all-cause mortality. Some analyses link reduction of high sodium intake (6,000 to 7,000 mg/day) to moderate sodium intake (defined as anywhere from 2,300 to 5,000 mg/day) with reduced cardiovascular risk or mortality, but suggest that low intake (defined as less than 2,000 mg/day up to 2,600 mg/day) may be associated with increased risk of death or major cardiovascular events.10,11

Rather than demonstrating actual health risk, however, other reviews say such findings result from methodological challenges of this research, including the following:

• Dietary sodium is difficult to accurately assess, since so much of it comes from processed foods in amounts that vary significantly between brands. Because of large day-to-day variation, the gold standard for assessing intake is urinary sodium from three to seven 24-hour collections.12,13 The studies that associate lowest sodium intake with increased health risks have included overnight or spot urinary samples, using an algorithm to estimate sodium intake, according to a 2016 analysis.10

• Disease and mortality endpoints develop over many years. So even a reliable estimate of sodium intake at one point in time cannot necessarily represent sodium intake in the 10 or 20 years before disease or death endpoints.

• Although observational studies attempt to adjust for confounding variables, factors associated with low sodium intake (such as older age and reduced physical activity) link to worse health outcomes. Moreover, the majority of the subjects in the 2016 analysis noted above were from a study that included large populations from China, Southern Asia, South America, the Middle East, and Africa.10 In these populations, with varying access to health care and overall diet quality, low sodium intake can reflect low total caloric intake and health risks related to poverty.12,13

Tasked with going beyond sodium and blood pressure to evaluate relationship to health outcomes, the IOM reported in 2013 that reducing sodium consumption from current US intake to 2,300 mg per day substantially decreases risk of heart disease and stroke, with no evidence of harm.14 However, the report concluded that evidence was insufficient and inconsistent on benefits or hazards in disease endpoints of reducing intake below 2,300 mg per day. Available studies don't have enough subjects and long enough follow-up to identify statistically significant differences in health outcomes related to sodium intake of 1,500 mg per day or less, according to the report. Since its publication, follow-up of more than 20 years from the Trials of Hypertension Prevention shows no increase in all-cause mortality with low dietary sodium.13 These studies, which assessed sodium intake via the recommended multiple 24-hour urine tests, showed 12% increased mortality for each 1,000-mg increase in sodium intake, starting from less than 1,500 mg per day.

Researchers in favor of reducing sodium below 2,300 mg per day when possible, at least in high-risk groups, say this is appropriate, given the methodological problems of following enough people on very low-sodium diets for enough years to detect differences in health outcomes. They argue that we can connect the dots of well-established studies on sodium and blood pressure, which demonstrate that 1,500 mg of sodium per day lowers blood pressure even more than intake of 2,300 mg per day, with other studies that identify hypertension as a major cause of US cardiovascular events and deaths, and of end-stage renal disease.1,7

The National Academy of Sciences is in the process of developing updated Dietary Reference Intakes for sodium and potassium that will include consideration of effects on CVD and other health outcomes.

Are There Special Cases?
As noted, some recommendations suggest that lower sodium intake is especially advised for people whose blood pressure tends to be more sodium sensitive or who are at greater cardiovascular risk.7 Yet, there also are questions about whether some people should be wary of the "lower is better" mantra. The 2013 IOM report found some evidence suggesting risk of adverse health outcomes associated with sodium intake levels in ranges approximately between 1,500 and 2,300 mg per day among those with diabetes, kidney disease, or CVD.14 The report concluded that the evidence on direct health outcomes isn't strong enough to suggest that they should be treated differently than the general US population and doesn't support recommendations to lower sodium intake within these subgroups to 1,500 mg per day. It's noteworthy that analyses showing no risk associated with very low sodium intake didn't include people with diabetes or heart disease other than hypertension.4,13

Reduced sodium intake has become a standard part of care for heart failure patients. One six-month randomized controlled trial of patients with heart failure (New York Heart Association classes II and III) showed that sodium intake of 1,500 mg per day or less was associated with improved quality of life compared with higher intake.15 However, the 2013 IOM report noted some studies linking sodium reduction to greater risk of adverse health effects in patients who have moderate or severe congestive heart failure and are receiving aggressive diuretic therapy and are on fluid restriction.14

According to the Academy of Nutrition and Dietetics Evidence Analysis Library® systematic review*, both excessive sodium intake (above 2,800 to 3,000 mg per day) and very low sodium intake (1,800 to 1,900 mg per day or less) pose a hazard that may lead to poor outcomes in heart failure patients.16 The 2017 Heart Failure recommendation (rated Fair, Imperative) is for individualized sodium and fluid intake to be within the ranges of 2,000 and 3,000 mg sodium per day and 1 to 2 L fluid per day. Intake within these ranges reportedly improved quality measures (eg, readmissions rate, length of stay, and mortality rate), renal function and clinical laboratory measures, symptom burden, and body weight.

Importance of Overall Dietary Pattern
Although dietary sodium reduction from current levels decreases blood pressure as a stand-alone change, the same reduction in dietary sodium lowers blood pressure further as part of adopting an eating pattern exemplified by the DASH diet.3 This eating pattern, compared with typical US diets, increases vegetables, fruits, low-fat dairy products, whole grains, poultry, fish, and nuts, and decreases saturated fat, red meat, sweets, and sugar-sweetened beverages.

In the original DASH-Sodium trial, a DASH-style eating pattern combined with sodium limited to 1,150 mg per day, lowered systolic blood pressure 8.9 mm Hg and diastolic blood pressure 4.5 mm Hg compared with an average US diet and 3,500 mg sodium.3 A DASH-type diet brings the greatest blood pressure reduction in those with hypertension and in those with higher sodium intake.3,17

The new ACC/AHA clinical practice guidelines on high blood pressure recommend a DASH-style eating pattern.1 Recommendations also advise 3,500 to 5,000 mg per day of dietary potassium, although lower amounts may be needed with chronic kidney disease or use of medications that reduce potassium excretion. Potassium increases sodium excretion and acts in several pathways to counterbalance effects of excess sodium on vasoconstriction that can elevate blood pressure.

The DASH diet does increase vegetable and fruit consumption and potassium intake compared with a standard American diet. But it's important to recognize that the original DASH trial showed that this eating pattern reduced blood pressure more than was achieved by increased vegetables and fruits alone.18 Although potassium intake increases with greater consumption of fruits and vegetables, blood pressure reduction also may stem from increases in magnesium, calcium, nitrate, and polyphenol phytochemicals. Acting through multiple mechanisms, limited animal and human research suggests that each of these nutrients and compounds may promote endothelial vasodilation and inhibit blood vessel constriction that can elevate blood pressure.19-24

Beyond sodium alone, it's also important to consider weight when evaluating steps that are accessible and effective for decreasing blood pressure. According to the new clinical practice guideline for high blood pressure, people with overweight or obesity who reach an ideal weight can achieve greatest blood pressure reduction.1 But the guideline advises aiming to lose at least 1 kg and notes that for each kg of weight loss, systolic blood pressure can be expected to decrease about 1 mm Hg.

Putting Sodium Reduction Into Practice
In addition to a general assessment of overall diet quality, since the majority of Americans' sodium consumption comes from processed foods, it's helpful to investigate amounts and choices within the food categories that all together provide more than one-half of the sodium in the average American diet. These, according to the DGA, include mixed dishes (eg, burgers, sandwiches, and tacos); rice, pasta, and grain dishes; pizza; meat, poultry, and seafood dishes; and soups.

The AHA has singled out the "Salty Six," which provide 42% of average US intake: sandwiches, pizza, bread, poultry, soup, and deli meat. An additional 13% of average intake comes from grain-based mixed dishes and meat, poultry, and seafood mixed dishes. Other foods that may contribute significant amounts for some people include savory snack foods, condiments, cheese, and processed vegetables and legumes.

Considering overall diet quality and individual circumstances, priorities can be set for reducing dietary sodium in the context of promoting other qualities of a DASH-style diet and appropriate calorie consumption.

Label reading is an important part of education to reduce sodium intake and can pose a real challenge to consumers. The wording of FDA-approved nutrient claims on labels differs according to the amount of sodium the FDA allows for each claim.25 Some refer to amount in a standard serving size as defined on the label (salt/sodium-free: less than 5 mg; very low sodium: 35 mg or less; or low sodium: 140 mg or less). Others identify sodium content lower than in the "regular" version of the product (but not necessarily lower than all "regular" versions); reduced sodium means at least 25% less sodium, while light in sodium or lightly salted denotes at least 50% less sodium.

As an example, for someone who eats a canned soup that supplies 690 mg sodium per cup every day for lunch, switching to a reduced-sodium option offers a significant step toward the goal of reducing intake by 1,000 mg per day, especially if the ordinary portion is larger than one cup. However, if the goal is 1,500 mg sodium per day, then even the reduced-sodium option will supply more than one-third of the day's total and likely not be an appropriate choice.

Looking for the AHA's Heart-Check Food Certification Program's logo can be a good start. But sodium content criteria vary by food category. For example, approved fruits, plain pasta, or grains such as rice or barley can have no more than 140 mg sodium per serving, corresponding to the FDA definition of low sodium. However, crackers and cheese may have up to 240 mg per standard serving, soups up to 480 mg, and main dishes or dinners up to 600 mg.26,27

Depending on an individual's baseline food choices, it's possible to cut 1,000 to 2,000 mg sodium per day by swapping frequently used high-sodium processed foods for lower-sodium options. Each of the following swaps cuts at least 200 to 500 mg per serving:

• instant flavored oatmeal for one-minute quick-cooking oatmeal;
• flavored rice and grain mixes for unflavored grains and add herbs of choice;
• canned vegetables for fresh, plain frozen (no sauce) or no-salt-added canned;
• spaghetti sauce for no-salt-added tomatoes or tomato paste, and add herbs; and
• processed cheese for natural cheese, ideally with sharper flavor to allow for smaller portions.

If a very low sodium level is targeted, these swaps may not be enough, and more substantial changes in a wide range of food selections and eating out likely will be needed.

The bottom line, then, is that even if lowering dietary sodium to 2,300 mg per day—or even 1,500 mg per day—may produce the greatest decrease in blood pressure, dietitians can assess patient readiness to achieve these targets. Even reducing sodium intake by 1,000 mg per day can have a clinically significant effect on blood pressure. And this can be combined with a DASH-style diet, physical activity, limits on alcohol use, and steps to lower calorie intake to make a clinically important reduction in blood pressure that may be more achievable than aggressive sodium restriction.

— Karen Collins, MS, RDN, CDN, FAND, is a nutrition consultant specializing in cancer prevention and cardiometabolic health.

* Academy of Nutrition and Dietetics Evidence-Based Nutrition Practice Guidelines are intended to serve as a synthesis of the best evidence available to inform registered dietitians as they individualize nutrition care for their clients. Guidelines are provided with the express understanding that they do not establish or specify particular standards of care, whether legal, medical, or other. Evidence-Based Nutrition Practice Guidelines are intended to summarize best available research as a decision tool for Academy members.

[Sidebar]

CURRENT US ADULT INTAKE
• Average sodium intake: 3,529 mg sodium per day.*
• Ninety-seven percent of men and 81% of women exceed 2,300 mg sodium intake per day.**
• The lowest fifth percentile of adult intake (ie, 95% of people exceed this level) is 2,500 mg per day for men and 1,840 mg per day for women.**

* Based on NHANES, 2013–2014
** Based on NHANES, 2007–2010

— KC


References
1. Whelton PK, Carey RM, Aronow WS, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines [published online November 13, 2017]. Hypertension. doi: 10.1161/HYP.0000000000000065.

2. Office of Disease Prevention and Health Promotion. Appendix E-2.1: usual intake distributions, 2007-2010, by age/gender groups. https://health.gov/dietaryguidelines/2015-BINDER/meeting2/docs/refMaterials/Usual_Intake_072013.pdf. Published July 2013.

3. Sacks FM, Svetkey LP, Vollmer WM, et al. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. N Engl J Med. 2001;344(1):3-10.

4. He FJ, Li J, MacGregor GA. Effect of longer-term modest salt reduction on blood pressure. Cochrane Database Syst Rev. 2013;4:CD004937.

5. US Department of Health & Human Services. Dietary Guidelines for Americans 2015–2020: Eighth Edition. http://health.gov/dietaryguidelines/2015/guidelines/. Published January 7, 2016. Accessed November 27, 2017.

6. Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press; 2005.

7. Appel LJ, American Society of Hypertension Writing Group, Giles TD, et al. ASH position paper: dietary approaches to lower blood pressure. J Clin Hypertens (Greenwich). 2009;11(7):358-368.

8. Alderman MH, Cohen HW. Dietary sodium intake and cardiovascular mortality: controversy resolved? Curr Hypertens Rep. 2012;14(3):193-201.

9. Aburto NJ, Ziolkovska A, Hooper L, Elliott P, Cappuccio FP, Meerpohl JJ. Effect of lower sodium intake on health: systematic review and meta-analyses. BMJ. 2013;346:f1326.

10. Mente A, O'Donnell M, Rangarajan S, et al. Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies. Lancet. 2016;388(10043):465-475.

11. Graudal N, Jürgens G, Baslund B, Alderman MH. Compared with usual sodium intake, low- and excessive-sodium diets are associated with increased mortality: a meta-analysis. Am J Hypertens. 2014;27(9):1129-1137.

12. Cobb LK, Anderson CA, Elliott P, et al. Methodological issues in cohort studies that relate sodium intake to cardiovascular disease outcomes: a science advisory from the American Heart Association. Circulation. 2014;129(10):1173-1186.

13. Cook NR, Appel LJ, Whelton PK. Sodium intake and all-cause mortality over 20 years in the Trials of Hypertension Prevention. J Am Coll Cardiol. 2016;68(15):1609-1617.

14. Institute of Medicine. Sodium Intake in Populations: Assessment of Evidence. Washington, DC: The National Academies Press; 2013.

15. Colin-Ramirez E, McAlister FA, Zheng Y, Sharma S, Armstrong PW, Ezekowitz JA. The long-term effects of dietary sodium restriction on clinical outcomes in patients with heart failure. The SODIUM-HF (Study of Dietary Intervention Under 100 mmol in Heart Failure): a pilot study. Am Heart J. 2015;169(2):274-281.e1.

16. Heart failure (HF) guideline (2017). Academy of Nutrition and Dietetics Evidence Analysis Library website. https://www.andeal.org/topic.cfm?menu=5289&cat=5227. Accessed December 1, 2017.

17. Juraschek SP, Miller ER 3rd, Weaver CM, Appel LJ. Effects of sodium reduction and the DASH Diet in relation to baseline blood pressure. J Am Coll Cardiol. 2017;70(23):2841-2848.

18. Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med. 1997;336(16):1117-1124.

19. Houston MC, Harper KJ. Potassium, magnesium, and calcium: their role in both the cause and treatment of hypertension. J Clin Hypertens (Greenwich). 2008;10(7 Suppl 2):3-11.

20. Houston M. The role of magnesium in hypertension and cardiovascular disease. J Clin Hypertens (Greenwich). 2011;13(11):843-847.

21. Volpe SL. Magnesium in disease prevention and overall health. Adv Nutr. 2013;4(3):378S-383S.

22. Hobbs DA, George TW, Lovegrove JA. The effects of dietary nitrate on blood pressure and endothelial function: a review of human intervention studies. Nutr Res Rev. 2013;26(2):210-222.

23. Landberg R, Naidoo N, van Dam RM. Diet and endothelial function: from individual components to dietary patterns. Curr Opin Lipidol. 2012;23(2):147-155.

24. Clark JL, Zahradka P, Taylor CG. Efficacy of flavonoids in the management of high blood pressure. Nutr Rev. 2015;73(12):799-822.

25. Use the nutrition facts label and reduce your intake of sodium in your diet. US Food & Drug Administration website. https://www.fda.gov/food/ingredientspackaginglabeling/labelingnutrition/ucm315393.htm. Updated January 3, 2018.

26. Heart-Check Food Certification Program nutrition requirements. American Heart Association website. http://www.heart.org/HEARTORG/HealthyLiving/HealthyEating/Heart-CheckMarkCertification/Heart-Check-Food-Certification-Program-Nutrition-Requirements_UCM_300914_Article.jsp#.WiRTQLpFzIU. Updated June 7, 2017. Accessed November 21, 2017.

27. Heart-Check Food Certification Program sodium limits by category. American Heart Association website. http://www.heart.org/idc/groups/heart-public/@wcm/@fc/documents/downloadable/ucm_461669.pdf. Published February 2015. Accessed November 21, 2017.

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