American Journal of Clinical Nutrition, Vol. 73, No. 3, 662-663,
March 2001
© 2001 American Society for Clinical Nutrition
The salt controversy at the turn of the century: no to prejudiced thinking, yes to concerted action
P Strazzullo
Department of Clinical and Experimental Medicine Federico II, University of Naples Medical School Naples Italy
Dear Sir:
The articles by McCarron (1) and Kaplan (2) on the US dietary guidelines for sodium effectively synthesize the opposite views of detractors and supporters of the "salt hypothesis." The evidence in favor of each respective thesis is presented with vigor and brightness. Having said that I personally share Kaplan's conclusive remarks, my concern is whether this type of antagonistic approach to the problem offers a true perspective to health professionals and to the population at large or, rather, perpetuates a long-lasting scientific conflict that, I believe, has been itself a major obstacle to large-scale implementation of lifestyle modifications for prevention and treatment of hypertension. Indeed, as Kaplan brilliantly pointed out in his textbook on clinical hypertension (3), nonpharmacologic measures are proposed as initial therapy for most patients by all official guidelines; practitioners recommend them more now than ever before but implement them as poorly as ever. What is the reason for this discrepancy? How much of the continued medical education highlights the merits of pharmacologic therapy and how much does it promote the implementation of nonpharmacologic measures recommended in the guidelines? Would it not be better to recognize that pharmaceutical companies are probably as interested in the implementation of dietary salt reduction as is the lobby of salt producers?
Convinced as I am of the importance of dietary salt in the etiology of hypertension, I believe that it is indeed time to waive the conflict-based approach and have interested scientists look at the several issues on the table. All should be respectful of each other's positions and bring their own experience to the discussion with the purpose of having a sincere interchange and taking a step forward (4).
Having read McCarron's and Kaplan's articles with as unbiased an attitude as I was able, I have concluded that at least a few points in their conflicting positions could be good starting points for positive action.
- McCarron stated, "... although dietary salt does play a role, it is not the archenemy of normal blood pressure regulation." May I presume that if salt is no longer identified as the "archenemy" of blood pressure control, McCarron would be eager to sit at the table and concentrate on the good reasons for salt playing a role?
- McCarron also admitted that "salt-sensitivity has now been shown to be a reproducible phenomenon..., although as yet there is not a specific definition of what constitutes a salt-sensitive response...." The acceptance of salt-sensitivity as a reproducible phenomenon is in accordance with a role for salt in blood pressure regulation. It is difficult to disagree on the lack of a practical way to detect salt sensitivity. Therefore, could all of us try and find new avenues for improving our knowledge of such a crucial aspect of the problem? Could we focus on the very fact that most of the monogenic forms of hypertension so far identified imply a deficit in renal sodium handling (4)?
- If there is agreement on the lack of evidence of substantial benefit for normotensive people from short-term trials of NaCl restriction (1), would McCarron turn his attention less reluctantly to the evidence of long-term benefit from salt reduction in chimpanzees (5) and consider its relevance to hypertension in humans?
- May we expect that recognition of the limited applicability of the INTERSALT study results in predicting the large-scale effects of lifestyle modifications (1) will be followed by the acknowledgment of the major limitations that make Alderman et al's study on sodium intake and cardiovascular mortality inconclusive (6)?
- Finally, how do we challenge McCarron's contention that the potassium and calcium contents of Western diets are definitely too low in the same way that their NaCl content is too high? Having realized that dozens of guidelines by scientific societies and hundreds of authoritative expert recommendations over the years have not convinced people—or general practitioners—to reduce NaCl intake to any extent, would it not be wise to consider a different approach to the problem and speak in terms of complex dietary changes that include, of course, substantial NaCl restriction?
At the turn of the century, we can no longer afford to go on with the sterile dilemma "to salt or not to salt." Let us give up the conflict, abandon prejudiced thinking, agree on what is already clear, and build up valuable new knowledge based on unprejudiced observations and well-designed experiments.
REFERENCES
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McCarron DA. The dietary guideline for sodium: should we shake it up? Yes! Am J Clin Nutr 2000;71:1013–9.[Abstract/Free Full Text]
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Kaplan NM. The dietary guideline for sodium: should we shake it up? No. Am J Clin Nutr 2000;71:1020–6.[Abstract/Free Full Text]
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Kaplan NM. Clinical hypertension. 7th ed. Baltimore: Williams and Wilkins, 1998.[Medline]
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Siani A, Guglielmucci F, Farinaro E, Strazzullo P. Increasing evidence for the role of salt and salt-sensitivity in hypertension. Nutr Metab Cardiovasc Dis 2000;10:93–100.[Medline]
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Denton D, Weisinger R, Mundy NI, et al. The effect of increased salt intake on blood pressure of chimpanzees. Nat Med 1995;1:1009–16.[Medline]
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Alderman MH, Madhavan S, Cohen H, et al. Low urinary sodium is associated with greater risk of myocardial infarction among treated hypertensive men. Hypertension 1995;25:1144–52.[Abstract/Free Full Text]
