Recently public health experts have decided that everyone needs to restrict their salt intake. But is sodium restriction really the best thing for everyone? The question is much more contentious than you might think.
The battle lines are fairly clear.
On one side are the National Heart, Lung, and Blood Institute, the National High Blood Pressure Education Program, the Institute of Medicine, and academic experts on hypertension whose careers have been based on funding from these organizations. These parties have long held that it is important to restrict dietary salt as a matter of public policy, for the purpose of reducing the incidence of hypertension worldwide. They cite scores of scientific studies bolstering their argument, and conclude that widespread salt restriction is the best public policy.
On the other side is the Salt Institute, the big manufacturers of processed foods, and other academic experts (whose careers have enjoyed funding from these sources). These parties cite scores of scientific studies bolstering their argument that widespread salt restriction would be bad public policy and possibly dangerous.
Both camps are entrenched, well-armed, and after over 30 years of fighting, battle-hardened.
The Theory of General Salt Restriction - Pros and ConsThe theory that says that salt restriction would make good public policy is based on epidemiological studies (particularly, the Intersalt study), which suggest that restricting salt would lead to a small reduction in the average blood pressure of the population, sufficient to greatly reduce the incidence of hypertension, which, in turn, should reduce the incidence of heart disease and stroke.
Critics of such a public policy make two arguments. First, they point out that no actual prospective, controlled study has ever been done showing that restricting salt in the general population would either reduce the population's average blood pressure or improve the population's outcomes. Second, they point out that sodium has many effects on physiology aside from controlling blood pressure, that several of these "other" effects of sodium restriction could be decidedly negative, and that in the past, other broad, population-wide recommendations made by overly confident "experts" have not turned out well. (They cite the recommendation for hormone replacement therapy for most postmenopausal women, the widespread introduction of man-made trans-fats into our food chain as a health measure, and, possibly, the widespread recommendation for high-carb, low-fat diets.)
Do All People Respond the Same to Dietary Salt?No. Some people appear to be "salt sensitive," which means that increased salt intake tends to either increase their blood pressure, "stiffen" their blood vessels, or both. Salt sensitivity probably occurs in 10 - 20% of the population, and is thought to be related to genetic factors, race, age, body mass, and fitness level. These individuals indeed have a high incidence of hypertension.
Unfortunately, there is no routine or easy method of detecting whether an individual is salt sensitive - except to say that if you have hypertension, the odds that you also have salt sensitivity are pretty high. (This is why at least a trial of a salt-restricting diet is recommended in patients with hypertension.)
What About People Without Salt Sensitivity?If everyone were salt sensitive, or if there were no medical downside to salt restriction in people who were not salt sensitive, then the only argument against recommending a population-wide policy of salt restriction would be an economic (or possibly political) one. Unfortunately, there are several ways that restricting salt might be detrimental to some people, at least in theory. This should not be particularly surprising, since sodium plays an extremely important role in many processes in our bodies, and not in just blood pressure control.
Sodium, just as one example, plays an important role in regulating the renin/angiotensin system (an extremely important hormonal pathway that helps regulate blood pressure, fluid balance, kidney function, vascular tone, and probably a few other things). Restricting sodium intake increases renin levels, which can have numerous adverse effects in people who are not salt sensitive. Indeed, in some people, blood pressure actually increases with sodium restriction.
So Who Is Right?Nobody knows. But I have lived long enough to become quite skeptical about the actual expertise of the experts when it comes to public health. Before they take any action to go beyond mere "recommendations" regarding the general population's salt intake, I personally would like to see a prospective, randomized, controlled study on whether the good actually outweighs the bad when salt intake is broadly restricted across a population. Even then, since it seems likely that salt restriction would help some people but harm others, I would like to see studies that would help us determine which individuals are which, before we all are herded into a one-size-fits-all approach to dietary salt.
Should You Be On A Salt Restrictive Diet?Despite the controversy surrounding the recommendation for a population-wide salt restriction, most experts agree that if you have hypertension, salt restriction should be part of the initial step in attempting to control your blood pressure.
In addition, anyone who has a medical condition that causes sodium and fluid retention -- especially heart failure and certain types of kidney or liver disease -- should be on a strict salt restrictive diet.
Alderman MH. Dietary Sodium and Cardiovascular Health in Hypertensive Patients: The Case against Universal Sodium Restriction. J Am Soc Nephrol (2004)15:S47-S50.
Elliott P, Stamler J, Nichols R, et al. Intersalt revisited: Further analyses of 24 hour sodium excretion and blood pressure within and across populations. British Medical Journal 1996; 312:1249.
Franco V, Oparil S. Salt Sensitivity, a Determinant of Blood Pressure, Cardiovascular Disease and Survival. Int. J. Epidemiol. (2002) 31 (2): 311-316. doi: 10.1093/ije/31.2.311.