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In Reply—Population-wide Sodium Reduction: Reasons to Resist

      A discussion of salt intake always generates a vigorous debate. In some part, controversy occurs because of the years of study generally required to determine the effect of dietary modifications on morbidity and mortality. Perhaps as a result, association studies have proliferated in this area to replace randomized controlled trials. However, the field of nephrology in particular has learned a series of “tough lessons” as a result of relying on observational data and is now emphasizing the need for randomized controlled studies to dictate clinical practice. With this background, DiNicolantonio et al bring forward several interesting observations that merit additional comment.
      DiNicolantonio et al claim that reducing salt intake may increase renin, aldosterone, adrenaline, noradrenaline, cholesterol, and triglyceride levels. Although the examination of these associations of dietary sodium intake with the renin-angiotensin-aldosterone system is of interest, the primary consideration should be hard end points such as mortality and not just an association with renin levels. The potential issue of the effect of a low-salt diet on insulin levels is also mentioned, but perhaps caloric intake in our modern society should be considered the primary cause of hyperinsulinemia and not a low-salt diet. In addition, clinical outcomes—not necessarily associations with insulin levels—should be the preferred end point when determining the optimal mode of sodium management in patients who have (or are at risk for) diabetes mellitus.
      DiNicolantonio et al quote a meta-analysis by Graudal et al
      • Graudal N.A.
      • Galløe A.M.
      • Garred P.
      Effects of sodium restriction on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride: a meta-analysis.
      that derived data from sudden and large reductions in salt intake and ignored contrary evidence.
      • Aburto N.J.
      • Ziolkovska A.
      • Hooper L.
      • Elliott P.
      • Cappuccio F.P.
      • Meerpohl J.J.
      Effect of lower sodium intake on health: systematic review and meta-analyses.
      The underlying rationale for the inconsistent findings in the report by Graudal et al is that a drastic reduction in dietary sodium intake can lead to unfavorable metabolic and neurohormonal alterations, which could promote insulin resistance, lipid abnormalities, and increased cardiovascular risk through a compensatory activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system (activation that is proportional to the degree of sodium reduction).
      • Graudal N.A.
      • Galløe A.M.
      • Garred P.
      Effects of sodium restriction on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride: a meta-analysis.
      • Grassi G.
      • Dell'Oro R.
      • Seravalle G.
      • Foglia G.
      • Trevano F.Q.
      • Mancia G.
      Short- and long-term neuroadrenergic effects of moderate dietary sodium restriction in essential hypertension.
      The theory seems to be valid only for an extremely low sodium intake
      • Alderman M.H.
      • Cohen H.
      • Madhavan S.
      Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I).
      and not for the 2300 mg/d recommended for the general population.

      US Department of Health and Human Services. Dietary Guidelines for Americans, 2010. http://www.health.gov/dietaryguidelines/2010.asp. Updated January 15, 2014. Accessed December 2, 2013.

      Moderate salt reduction in the United States is unlikely to have a major impact on iodine status or exercise-associated hyponatremia. Most salt in the diet is derived from processed foods, and the salt used in food processing in the United States is typically not iodized.
      • Becker D.V.
      • Braverman L.E.
      • Delange F.
      • et al.
      Public Health Committee of the American Thyroid Association
      Iodine supplementation for pregnancy and lactation—United States and Canada: recommendations of the American Thyroid Association.
      Encouraging the food industry to use iodized salt during processing or alternative fortification strategies is more likely to yield optimal iodine status in Americans.
      • Tonacchera M.
      • Dimida A.
      • De Servi M.
      • et al.
      Iodine fortification of vegetables improves human iodine nutrition: in vivo evidence for a new model of iodine prophylaxis.
      • Zimmermann M.B.
      • Andersson M.
      Assessment of iodine nutrition in populations: past, present, and future.
      Although careful population monitoring for iodine status is required, countries that mandate iodization of salt used in processing and for personal consumption have found that lower salt intakes do not compromise iodine status.
      • Charlton K.E.
      • Jooste P.L.
      • Steyn K.
      • Levitt N.S.
      • Ghosh A.
      A lowered salt intake does not compromise iodine status in Cape Town, South Africa, where salt iodization is mandatory.
      In contrast to the statement by DiNicolantonio et al, most cases of exercise-associated hyponatremia are due to excessive water consumption rather than a lack of salt in the diet.
      • Almond C.S.
      • Shin A.Y.
      • Fortescue E.B.
      • et al.
      Hyponatremia among runners in the Boston Marathon.
      • Montain S.J.
      • Cheuvront S.N.
      • Sawka M.N.
      Exercise associated hyponatraemia: quantitative analysis to understand the aetiology.
      • Rosner M.H.
      • Kirven J.
      Exercise-associated hyponatremia.
      Finally, in regard to the statement on congestive heart failure (CHF), our review excluded studies with CHF as the main outcome. However, a caveat in the discussion section of our article
      • Aaron K.J.
      • Sanders P.W.
      Role of dietary salt and potassium intake in cardiovascular health and disease: a review of the evidence.
      stated that clinicians should be aware that patients with severe CHF take multiple medications that inhibit or block the renin-angiotensin-aldosterone system and thus may not benefit from salt restriction.
      • Paterna S.
      • Gaspare P.
      • Fasullo S.
      • Sarullo F.M.
      • Di Pasquale P.
      Normal-sodium diet compared with low-sodium diet in compensated congestive heart failure: is sodium an old enemy or a new friend?.
      Less rigorous targets for salt reduction may be appropriate for certain groups of patients with CHF or multiple comorbid conditions.
      It is currently impossible for clinicians to provide strictly individualized dietary recommendations to the general population because the approach would require them to have already outlined nutrigenomic interactions and underlying genetic susceptibility traits, the identification of which, at present, remains an evolving and challenging field of research.
      • Corella D.
      • Ordovas J.M.
      Nutrigenomics in cardiovascular medicine.
      Based on the current evidence, and until the response of most individuals to dietary manipulations can be fully distinguished, the hemodynamic benefits of a reduced-sodium diet appear to far outweigh any theoretical metabolic or hormonal perils following dietary salt reduction.
      • Koliaki C.
      • Katsilambros N.
      Dietary sodium, potassium, and alcohol: key players in the pathophysiology, prevention, and treatment of human hypertension.
      There is evidence that supports a reduction in salt intake for the general population, including outcome trial evidence on cardiovascular disease.
      • Cook N.R.
      • Cutler J.A.
      • Obarzanek E.
      • et al.
      Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP).
      The effects of nonpharmacologic interventions on blood pressure of persons with high normal levels: results of the Trials of Hypertension Prevention, Phase I.
      • Cappuccio F.P.
      • Markandu N.D.
      • Carney C.
      • Sagnella G.A.
      • MacGregor G.A.
      Double-blind randomised trial of modest salt restriction in older people.
      • Jessani S.
      • Hatcher J.
      • Chaturvedi N.
      • Jafar T.H.
      Effect of low vs. high dietary sodium on blood pressure levels in a normotensive Indo-Asian population.
      Historically, salt intake was low in preindustrial societies, and intakes have only reached high amounts in the past century. The food industry has contributed to this increase.
      • Eaton S.B.
      • Konner M.
      Paleolithic nutrition: a consideration of its nature and current implications.
      • Popkin B.M.
      Nutritional patterns and transitions.
      • Konner M.
      • Eaton S.B.
      Paleolithic nutrition: twenty-five years later.
      Of all public health policies, comprehensive salt reduction programs represent some of the most practical and cost-effective strategies for chronic disease prevention,
      • Asaria P.
      • Chisholm D.
      • Mathers C.
      • Ezzati M.
      • Beaglehole R.
      Chronic disease prevention: health effects and financial costs of strategies to reduce salt intake and control tobacco use.
      • Cappuccio F.P.
      • Capewell S.
      • Lincoln P.
      • McPherson K.
      Policy options to reduce population salt intake.
      but they need the cooperation of the food industry, multiple levels of government, and other diverse stakeholders.
      • Cappuccio F.P.
      • Capewell S.
      • Lincoln P.
      • McPherson K.
      Policy options to reduce population salt intake.
      Centers for Disease Control and Prevention (CDC)
      CDC Grand Rounds: dietary sodium reduction—time for choice.
      If this goal was accomplished, the projected health and economic benefits of preventing hypertension, stroke, myocardial infarction, and early mortality would be considerable.
      • Coxson P.G.
      • Cook N.R.
      • Joffres M.
      • et al.
      Mortality benefits from US population-wide reduction in sodium consumption: projections from 3 modeling approaches.
      • He F.J.
      • MacGregor G.A.
      Salt, blood pressure and cardiovascular disease.
      Consequently, we would like to reinforce the concept that the consumption of a low-sodium/high-potassium diet is a critical strategy for promoting cardiovascular health and for preventing and treating hypertension and cardiovascular disease in the US population.

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      Linked Article

      • Population-wide Sodium Reduction: Reasons to Resist
        Mayo Clinic ProceedingsVol. 89Issue 3
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          In their review article in the September 2013 issue of Mayo Clinic Proceedings, Aaron and Sanders1 stated that “high salt intake not only increases blood pressure but also plays a role in endothelial dysfunction, cardiovascular structure and function, albuminuria and kidney disease progression, and cardiovascular morbidity and mortality in the general population” and that “the body of evidence supports population-wide sodium intake reduction.” What the authors neglect to mention is that reducing sodium intake has been associated with increases in renin, aldosterone, adrenaline, noradrenaline, cholesterol, and triglyceride levels.
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