Commentary—Are Current Recommendations for Sodium Intake Appropriate?

5/25/2017 George Bakris, MD, Professor of Medicine, University of Chicago School of Medicine
A recent article by Moore, et al in the Journal of the Federation of American Societies for Experimental Biology reported results of a 16-yr longitudinal study of > 2600 normotensive patients in the Framingham Offspring Study (1). Patients were followed to evaluate the long-term effect of dietary sodium on blood pressure. Contrary to most clinician’s expectations, researchers found an inverse relationship between sodium intake and both systolic and diastolic BP; that is, mean SBP and DBP both progressively decreased with each quintile of increasing sodium intake.
The findings of the report by Moore et.al. are not too surprising as long as we remember to distinguish the role of sodium restriction in treatment versus prevention of hypertension. 
Regarding treatment, the data are overwhelming and clear that among those with hypertension, a diet with > 2300 mg/day of sodium contributes to poor BP control (2). This is in part because a high sodium intake suppresses the renin-angiotensin system, in which case, drugs such as ACE inhibitors and ARBs are relatively ineffective in lowering BP.
Regarding prevention of hypertension in normotensive people, data on sodium restriction are less clear. Several studies do suggest a beneficial effect but methodologic factors prevent them from being definitive. A study (3) of the DASH (Dietary Approaches to Stop Hypertension) diet that was done under carefully controlled conditions did clearly show that a low-sodium diet lowered BP among normotensive people. However, there were only 412 participants, half of whom had hypertension or prehypertension, leaving only a small number of normotensive patients. Furthermore, all meals were prepared by the researchers and only a narrow range of sodium intake was tested (1.5 to 3.3 gm/day). The diet also had a balance of other electrolytes, particularly potassium, magnesium and to a lesser extent calcium. The importance of these minerals in maintaining blood pressure homeostasis is clear from many studies and is often ignored (4). In everyday life, most people do not eat a balanced diet of all these minerals and hence, imbalance exists.
It is also worth pointing out that countries with very high sodium intake, such as Japan, the United Kingdom, and Finland, developed governmental guidance to reduce salt in processed foods bought by consumers (5). In a recent systematic review, a total of 75 countries now have a national salt reduction strategy (6). Over the past few decades, this significant reduction in sodium content of foods by as much as 50% in some countries has resulted uniformly in a reduced cardiovascular mortality (7). These data extend well beyond the Framingham study and show a mortality benefit by reducing sodium intake in the general diet. What is unclear is whether this population benefit was driven only by the positive effects on those with hypertension, or whether there was also a benefit in normotensive people.
Another factor to keep in mind regarding dietary recommendations is that people who are normotensive may later develop hypertension (and thus show apparent benefit from a low-sodium diet). People who are normotensive at age 50 have a 90% chance of being hypertensive if they live to age 80 (2).  
So, what is the right answer? The message is clear that excess of anything is not beneficial and is usually detrimental. Ignoring sodium intake such that daily consumption is upward of 5 to 6 grams a day or more or reducing intake to 1,000 mg are extremes and, as in all things in life, a compromise is in order. There is no major proven benefit on cardiovascular outcome from strict reduction in sodium in normotensive people. Consuming 3 to 4 grams of sodium daily should be not be detrimental provided patients have routine BP monitoring and remain normotensive; larger amounts of sodium may increase risk. However, those with hypertension clearly require a low sodium diet, and 2300 mg is very reasonable and has proven results.

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