Reducing sodium intake has been a nutritional mantra for decades. We have repeatedly been told that cutting back on salt lowers blood pressure which in turn lowers the risk of heart attacks and strokes. But these days it seems to be in vogue to question almost every type of dietary advice that has been dispensed by health authorities, including salt intake. Questioning current dogma of course isn’t a bad thing, after all, that is how science progresses. The truth is that often the evidence for recommendations is not as robust as it is made out to be and we have seen views change about the likes of saturated fats, eggs and sugar in our diet as new data emerge. Today, with studies being cranked out at a frantic pace it is possible to find “evidence” for almost any view that one holds, but conclusive evidence, particularly when it comes to diets, is elusive. When it comes to food, the gold standard, the randomized double-blind trial, is extremely difficult to design and carry out.
In the case of sodium, a meaningful trial would mean following groups of subjects for many years and noting the incidence of cardiovascular disease, with the only difference between groups being the amount of sodium in the diet. It is difficult enough to do this over the short term, but that actually has been done. The famous dietary approaches to fight hypertension (DASH) trial managed to test three different levels of sodium intake by providing subjects with all their meals. They consumed either 1500, 2300 or 3500 mg of sodium a day, with results showing a clear link between blood pressure and sodium intake. The 3500 mg level was chosen because it represents the amount of sodium that is consumed on the average by the population. This translates to about 9 grams of salt (sodium chloride), or one and a half teaspoons, most of which comes from processed foods.
The trial lasted only 16 weeks, too short to note a difference in disease patterns. As critics pointed out, demonstrating a decrease in blood pressure with reduced sodium is not the same as showing a decrease in the risk of a heart attack or stroke. But given that there is overwhelming evidence from population studies that high blood pressure is associated with cardiovascular disease, it is reasonable to recommend a cutback on salt. The question is by how much?
That question arises because some recent studies have suggested an increased risk of adverse health outcomes associated with sodium intake in the 1500 to 2300 mg a day range. This, however, may have nothing to do with sodium. It is possible that people with cardiovascular disease, who have been advised to dramatically reduce their salt intake, fall into this range and suffer problems because of the preexisting condition rather than their low sodium intake. In any case, for the general population, the 2300 mg target is reasonable. Debates about low sodium levels presenting a risk may have academic interest but have little practical value. The 1500 mg target is unattainable for most people, and given that our average intake is in the range of 3500 mg a day, emphasis has to be placed on reducing this rather than worrying about too little sodium.
Cutting back isn’t easy. Producers cater to our fondness for salt by adding it liberally to a wide array of foods. A bowl of cereal contains about 300 mg of sodium, a single hot dog can have 800, a slice of bread 230, a cup of cottage cheese 900, a couple of slices of processed cheese 700, and half a cup of commercial tomato sauce 600 mg. A slice of pizza can weigh in anywhere from 600 to 1500 mg of sodium per slice! Obviously it isn’t hard to surpass 2300 mg. So there really is no worry about consuming too little sodium, that isn’t happening in the real world. There is another reason we can dismiss the naysayers who claim that the evidence to support a low sodium diet is too weak. Cutting back on sodium means a decrease in processed food intake and an increase in fruits and vegetables. And there can be no argument against that.