Low Sodium Diet – Dangerous?

High potassium foods are foods that are low in sodium and high in potassium and that produce an alkaline urine. The low sodium aspect of the diet has been challenged in the past and continues to be challenged today. Because the argument is still heard that a low salt diet may be dangerous to healthy people, it is important to review how this argument started, why it was no good in the first place, and how much evidence there is against it.

Beginnings – Low Sodium Diet Danger

Low sodium diet danger - J-Curve
J-Curve of Sodium Mortality – Fact or Fiction?

Articles were published in the late 1990s, and there have been more since, that reported increased deaths with low sodium consumption. Two of the original articles are representative (1, 2). They reported an inverse relation of sodium and heart attacks or cardiovascular disease mortality. This inverse relationship became modified subsequently. Subsequent publications questioning the safety of a low sodium diet usually reported a J-shaped or a U-shaped curve to the graph of the relationship of sodium to mortality. These articles claimed that there was a higher mortality at a low sodium intake that dipped down to a low point at about what the average intake is in Westernized society. It then moved up to a higher mortality at higher levels of sodium, forming a J-shape or U-shape to the graph.

There have been multiple articles pointing out the flaws in the publications that make these claims. In 2002, publication of a series of commentaries between the main proponents and the main antagonists presented the main arguments for both sides of the argument. These commentaries provide a very nice summary of the main arguments still being used today for and against the recommended 2300 mg and 1500 mg levels of sodium.

The First Commentary

The original argument against a low sodium diet can be understood from two representative publications (1, 2) in the 1990s. There were a few other similar articles by the same authors, and other authors, during that period, and there have been multiple articles with similar conclusions since then. In the first of these commentaries (3) the main author of those first two articles, Dr Alderman, argues in favor of increased mortality from the low sodium intakes recommended by several medical organizations. He discussed two unique populations that he claimed supported this view.

The first population he discussed was the Kuna Indians in Panama. They were claimed to have the same sodium intake as the urban Kuna, but not have the increase in blood pressure of the urban Kuna. The findings of this publication have had some problems with acceptance. The authors stated that their study was a feasibility trial, but nonetheless reported their findings. The potassium and sodium content of the food items in the Kuna diet (reported in a separate report) did not correspond to the results of the research. And the methods used to collect estimates of food intake were flawed.

The Kuna were reported to consume considerable amounts of cocoa that had a high potassium content. Much of the remainder of their food had a high potassium to sodium ratio. This potassium would negate much of the cardiovascular effects from the increased sodium intake. Yet the estimated sodium and potassium intake did not correspond with this food composition.

The methods used to obtain these estimates of sodium and potassium have problems. There were two statements in the Kuna articles about how the researchers estimated the amount of sodium ingested. One method mentioned was estimation of sodium from a single 24 hour urine collection. However, the author stated that approximately 1/2 the collections were incomplete. In the second method of estimation, the Kuna participants were asked to estimate the number of teaspoons of salt they ate, as well as give estimates for other food items. The methods used to collect estimates of food intake have been objected to by an anthropologist, Jeffrey Barnes, as being inaccurate because of known cultural factors.

The author also discussed a 30 year observational study of some nuns who had low blood pressure. 144 nuns living in extreme seclusion had sodium intakes similar to women in a nearby community. They did not have the age-related blood pressure increase of the community women. The authors of the nun study felt the difference in blood pressure was due to psychosocial factors. There have been no confirmatory studies done.

This first commentary discussed the Intersalt study, which is a major study showing the importance of a low sodium diet. The commentary author misstated the findings of this extensive study, saying simply “no association between sodium intake and blood pressure” was found in the 48 cosmopolitan centers included in the study. Later in this post, the commentary by two of the authors of the Intersalt study refute this claim.

In his discussion of animal studies he quoted only a small amount of animal work in which he obfuscated the findings. The enormous body of animal work showing the response to high salt and low-salt intake he ignored and did not discuss at all. He also discussed the effect of sodium on renin, and misunderstood the effect of sodium on blood vessels. He did not discuss any other basic science.

There is an extensive body of basic science even prior to 2002 and this has only grown considerably since then. The basic science since 2002 has clarified even more how sodium and potassium interact. This science shows how sodium is easily conserved by the body and potassium is easily excreted. The post here discussed this beautiful recent work showing how the kidney does this.

The Second Commentary

There were 4 commentaries that followed Dr Alderman's. The first was by Dr Elliott and Dr Stamler who were two of the authors of the Intersalt study. This response, and the response of Dr MacGregor and Dr de Wardener were far more extensive than those of the proponents of the danger of a low sodium diet. The final response was briefer, but included a few publications not previously mentioned. It supported the safety of a low sodium diet. The response after the response of Dr Elliott and Dr Stamler was in support of the potential danger of a low sodium diet. It was quite brief, but discussed that other dietary factors may be responsible for any favorable effects.

The response (4) by Dr Elliott and Dr Stamler pointed out the major problems with the studies that challenge the effectiveness and safety of a low sodium diet. They also pointed out the major categories of studies that support a low sodium diet. The supporting studies that they mentioned include human experimental, epidemiological, anthropological, and human observational studies. The human observational studies alone numbered over 50.

They pointed out the results of the DASH-sodium study. This study supplied all the food to the participants, giving high accuracy to the sodium intake estimates. In this study, the participants were divided into 3 low sodium groups. Each of the 3 groups showed lower blood pressure as sodium was reduced.

The Intersalt study showed higher blood pressure was associated with higher sodium intake in 48 modern populations, as well as in 4 indigenous populations. Dr Alderman's assertion that there was no direct correlation of blood pressure with sodium was completely refuted by this study and in this commentary.

The Third Commentary

This commentary was followed by another commentary (5) by two other proponents questioning the effectiveness of the low sodium diet. These authors basically confused the issue by bringing in other aspects of diet as a possible reason for the effect of sodium. Because other aspects of diet were also changed in the DASH-sodium trial, the authors propose that the other aspects of diet may be responsible for the blood pressure effect. These other aspects may have contributed to lower blood pressure, but have less support in the literature than the support for the effect of sodium.

The Fourth Commentary

The penultimate commentary (6) is by Dr MacGregor and Dr de Wardener of the United Kingdom, who discussed even more studies showing the importance of a low sodium intake to reduce blood pressure. They discussed some of the articles that Dr Elliott and Dr Stamler discussed. But they included more clinical studies, and they also included more basic science articles. The authors discussed the lack of vascular disease and hypertension in the indigenous Yanomami, discussed in this post. They pointed out that the Yanomami develop vascular disease, diabetes and become overweight when they migrate to towns and adopt a western lifestyle. They do not differ from others living indigenous lifestyles who migrate to Western lifestyles, as discussed here.

These two authors discussed the Portuguese interventional study in which one village was given processed foods with less salt, and a second village that was kept on their normal diet. The first village's sodium intake was reduced by 50%, leading to lower blood pressure in that village. The second village had no change in blood pressure.

The basic science studies the authors discussed included some discussed here and here, showing effects of sodium on scarring of the heart and stiffening of the blood vessels. Additionally, they pointed out the possible conflict of interest of the author of the first commentary. That author has acted as a member of the Medical Advisory Board for the Salt Institute, which represents the salt manufacturers.

The Fifth Commentary

The final commentary (7) included many of the previously discussed reports, and added discussion of a few not previously discussed, such as 3 randomized controlled studies. These commentators also supported the safety of a low sodium diet as preventive for cardiovascular disease.

The Response

At the very end, there is a response by the original commentator, Dr Alderman, to the low sodium proponents. He basically argues that the “diets of millions of healthy people or hypertensive patients should be based on empirical evidence” that the recommended change would be beneficial. He ignores the finding that the weight of evidence in favor of the low sodium diet overwhelms the contrary evidence. And he ignores the evidence that basic science supports the high potassium, low sodium diet. The basic science also explains the contrary empirical evidence that he so favors. This basic science is consistent with damage from a prior high sodium, low potassium diet causing an increased risk of cardiovascular death, even when sodium is restricted.

Potassium Is Not Considered

Neither the authors who favored the effect of sodium on blood pressure, nor the authors who favored the lack of effect, and potential danger, of low sodium intake discuss the importance of potassium. Nor do they discuss the potassium sodium ratio. However this lack of consideration of potassium has been common throughout the medical literature, and does not in any way negate the importance of lowering sodium.

Sodium and potassium work in concert. More and more studies are showing the importance of the potassium sodium ratio as more and more physicians become aware of the basic science behind the ratio. The importance of potassium in no way negates the importance of a low sodium diet. It actually bolsters the importance of a low sodium diet, since less sodium improves the potassium sodium ratio if the amount of potassium is unchanged in the diet.

Although this series of point and counterpoint is from 2002, the same arguments are being heard today. Since that time there has continued to be an ever mounting, massive amount of basic science that demonstrates the importance of the potassium sodium ratio. More evidence of its effect on the cell membrane potential (electric field), and how the cell membrane potential affects kidney cells, adrenal gland cells, heart cells, and blood vessel cells appears every week.

Low Sodium Diet And Reverse Causation

The studies that started this debate in the medical community basically showed reverse causation. The people in these studies on a low sodium diet were already very ill with heart damage. They would be expected to have a higher rate of death from heart disease than those on a higher salt diet who were not so sick. Studies that have not included these highly ill patients have shown that sodium consumption all the way down to 1500 mg per day lowers, rather than increases, the risk of heart disease. The post last week discussed a very careful study showing this very clearly.

There are few areas in preventive medicine that have so much strong evidence in their favor. The evidence in favor of a diet with a high potassium sodium ratio for healthy people is overwhelming. Its value for the prevention of strokes, cardiovascular disease, and kidney disease is solid. And the evidence for its value in the prevention of even some other diseases is growing.
1. Low urinary sodium is associated with greater risk of myocardial infarction among treated hypertensive men. Alderman MH, Madhavan S, Cohen H, Sealey JE, Laragh JH. Hypertension. 1995 Jun;25(6):1144-52.

2. Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I). Alderman MH, Cohen H, Madhavan S. Lancet. 1998 Mar 14;351(9105):781-5.

3. Salt, blood pressure and health: a cautionary tale. Alderman MH. Int J Epidemiol. 2002 Apr;31(2):311-5.

4. Evidence on salt and blood pressure is consistent and persuasive. Elliott P, Stamler J. Int J Epidemiol. 2002 Apr;31(2):316-9; discussion 331-2.

5. Salt, blood pressure and public policy. Freeman DA, Petitti DB. Int J Epidemiol. 2002 Apr;31(2):319-20; discussion 331-2.

6. Salt, blood pressure and health. MacGregor G, de Wardener HE. Int J Epidemiol. 2002 Apr;31(2):320-7; discussion 331-2.

7. Salt intake, hypertension and risk of cardiovascular disease: an important public health challenge. He J, Whelton PK. Int J Epidemiol. 2002 Apr;31(2):327-31; discussion 331-2.

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