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BMJ No 7106 Volume 315

Letters Saturday 23 August 1997

Intersalt data

Salt Institute has continued to distort evidence

Editor,
Richard Hanneman, the president of the Salt Institute, has announced that the institute has filed a citizens' petition asking the United States Food and Drug Administration to rescind its permission for food manufacturers to make health claims on their products' labels about the relation between sodium and hypertension. In the press release accompanying this petition Hanneman uses as his main evidence a paper in Hypertension(1) and claims that "the only study of health outcomes of persons actually consuming low sodium diets over an extended time (over 4 years) found that the lowest sodium-consuming quarter of 1,900 hypertensive patients experienced more than 4 times as many heart attacks as the highest sodium-consuming quadrant" and therefore "the hypertensives consuming low sodium diets had dramatically increased risk of having heart attacks."

In this study there was no measurement of 24 hour urinary sodium excretion or assessment of sodium intake (either before or during the study) with the patients taking their usual sodium intake. The only measurement of 24 hour urinary sodium excretion was before entry to the study and after five days of salt restriction to stimulate the renin-angiotensin system. Laragh has consistently pointed out that one cannot subgroup patients by their renin concentrations unless their salt intake is temporarily reduced.(2) Twenty four hour urine excretion at the end of five days of salt restriction will in no way reflect either the patients' usual salt intake at that time or their daily salt intake over the next four years.(3)(4) Hanneman's claims, therefore, are a distortion of the evidence in this paper.

Distortion of scientific data as above indicates that the Salt Institute has an ulterior motive. It wishes to try to maintain the unnecessary and high salt content of processed food (which is often equivalent to that of seawater). The commercial reasons for this stance are not difficult to imagine. Firstly, the more salt that is added to processed food, particularly meat products, the more water can be added, thereby increasing the weight of the product with very little additional cost. Secondly, the more salt that is consumed the greater the fluid intake and thirst. Is it by chance that some manufacturers of soft drinks also own snack companies? It is sad, but perhaps not surprising, that commercial interests seem to give Hanneman and the Salt Institute a mandate to continue to distort and misrepresent studies. At the same time they ignore the mass of other evidence that clearly links high salt consumption not only to the development of high blood pressure(5) but also to cancer of the stomach(6) and suggests that it is a potential major aggravating factor in bone demineralisation.(7)

Graham MacGregor Professor

Blood Pressure Unit,
Department of Medicine,
St George's Hospital Medical School,
London SW17 0RE

References

1 Alderman M H, Madhavan S, Cohen H, Sealey J E, Laragh J H. Low urinary sodium is associated with greater risk of myocardial infarction among treated hypertensive men. Hypertension 1995;25:1144-52.

2 Alderman M H, Madhavan S, Ooi W L, Cohen H, Sealey J E, Laragh J H. Association of the renin-sodium profile with the risk of myocardial infarction in patients with hypertension. N Engl J Med 1991;324:1098-104.

3 MacGregor G A. Low urinary sodium and myocardial infarction. Hypertension 1996;27:156.

4 Meltzer J I. Low urinary sodium and myocardial infarction. Hypertension 1996;27:155.

5 MacGregor G A, Sever P S. Salt - overwhelming evidence but still no action: can a consensus be reached with the food industry? BMJ 1996;312:1287-9.

6 Joossens J, Hill M J, Elliott P, Stamler R, Stamler J, Lesaffre E, et al. Dietary salt, nitrate and stomach cancer mortality in 24 countries. Int J Epidemiol 1996;25:494-504.

7 Antonios T F T, MacGregor G A. Salt - more adverse effects. Lancet 1996;348:250-1.

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