Salt of the Earth
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I can’t tell you the number of times I have read articles regarding the effects of salt on health and mortality over my years in medical practice; however, I can tell you that it has been very many. In the August 14, 2014 issue of the New England Journal of Medicine there are three independent articles regarding the effects of sodium and potassium on human health. Some things we do know about the role of salt and health. For example if you have someone with even mild congestive heart problems and you give them a salt solution you can send them into florid heart failure. We also know that if we should significantly restrict the salt intake for someone with high blood pressure they will have their pressure decrease. However we really have little knowledge of how much salt in the diet is optimal for the average individual. The first article by Dr. Mente and colleagues showed the relationship between urinary sodium excretion and blood pressure. They showed that for every gram of increased excretion of sodium there was on about a 2 mmHg increase in the systolic pressure and about a 1 mm increase in diastolic pressure. The slope was greater for those with hypertension and the elderly. They noted that potassium excretion was inversely associated with systolic blood pressure with a steeper slope associated with persons with hypertension and increased age. While sodium excretion is related to sodium intake the actual sodium intake in this and the other studies was not determined. The second study of O’Donnell et al looked at the relationship between urinary sodium and potassium excretion and mortality as well as cardiovascular events. This study had about 100,000 people enrolled. They showed that for sodium excretion below about 4 g per day the risk of death and cardiovascular events increased and by the time it reached 1 g the risk was nearly double. Also when the sodium excretion rose above 4 g per day the risk increased however even at the maximum level of 12 g per day the risk was only 1.2 times the optimal results at 4 g. So if you have sodium excretion reflecting sodium intake than then for the average person one has to be very careful about too much sodium in the diet and too little sodium in the diet. Unfortunately the study did not present the renal status of the given populations so it is unclear if some of this effect is related to a greater number of persons with poor or selectively poor renal excretion in the subgroup of low renal sodium excretion. In my opinion, this study, while very interesting, adds even more confusion to the understanding of the role of sodium in human health. The third study of Mozaffarian et al estimates the effect of high blood pressure being induced by too much sodium intake and deaths from cardiovascular causes. The model implies that there would be worldwide about 1.6 million deaths per year from cardiovascular causes attributable to the consumption of more than 2 g of sodium per day. Unfortunately there are too many assumptions here and what we find is that this result is not consistent with the findings in the second study where low amounts of renal excretion of sodium mortality actually went up from 4 to 2 grams. Thus we are far away from really understanding this issue. One positive point however is that it appears that increase potassium intake may someday be proven to have a beneficial effect on blood pressure and mortality for the average individual. That stated of course we cannot forget that for someone who has renal failure excess potassium can actually be deadly.
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