The idea that almost all of us should be cutting back on salt intake to avoid high blood pressure is well-entrenched, not only in the popular mind, but in the minds of physicians. But how strong is the evidence for this view? James J. DiNicolantonio, Varshil Mehta and James O'Keefe question how valuable salt restriction is for the typical person in their American Medical Journal article “Is Salt a Culprit or an Innocent Bystander in Hypertension? A Hypothesis Challenging the Ancient Paradigm?” All quotations in this blog post are from that article.
Let’s clear up a few things:
There are enough different physical conditions that it seems likely that some people should cut back on salt intake. But are these rare conditions?
For those with high blood pressure, medications that reduce blood pressure do seem to save lives. That doesn’t speak to whether reducing salt intake is important.
People who eat a lot of salty food do seem to be less healthy. But maybe it is all the other bad things in typical types of salty food. After all, processed food tends to have a lot of salt and a lot of sugar.
One reason it seems unlikely that restricting salt intake is necessary for the typical person is that evolutionarily, it would have been necessary for the body to evolve mechanisms to get the right sodium level:
The human brain (hypothalamus) is wired to maintain salt (sodium) balance and hence controls our salt intake.12,42, 43 The biological reason behind this tight homeostatic regulation is that the maintenance of normal sodium levels in the extracellular fluid is required for life and for cellular processes to function properly. The transition process from marine milieu to land-based existence required the evolution of cells that were able to simulate the salty environment of their progenitor cells that existed in sea water.
If sodium levels get too high, the bodies of healthy individuals are good at getting rid of sodium:
Dietary salt has been considered as one of the most important etiologic causes of hypertension. However, according to a study conducted by Hall,82 increasing salt intake in individuals with normal kidney function “usually does not increase arterial pressure much because the kidneys rapidly eliminate the excess salt and blood volume is hardly altered.” Other studies also mention the same principal, saying that individuals with normal kidney functions eliminate excess dietary salt with ease.83, 84, 85, 86
If sodium levels get too low, people start (appropriately) craving salt:
In other words, bodily need drives salt intake. In fact, the low-salt advice may lead to salt cravings and an overconsumption of more processed foods to obtain the salt our physiology desires.12 However, nowadays, to get the salt our body needs we end up consuming salty processed foods (instead of naturally salty foods) and thus consume a greater amount of harmful dietary substances (eg, excess calories, added sugars, harmful fats, and artificial flavorings).12 Indeed, low-salt diets may inadvertently cause us to eat more added sugars. When we are deficient in salt there is an enhanced craving for it, but this does not mean we are addicted to salt.42, 43, 48, 49
If sodium levels get too low and you don’t eat salt, bad things can happen:
…exercise or physical work (particularly when done in a warm or hot environment) on a low-salt diet causes a 10-fold increased risk of heat exhaustion and prostration (characterized by nausea, vomiting, tachycardia, hypotension, vertigo, dehydration, and collapse).36 Moreover, following the advice to consume <2300 mg of sodium per day can lead to negative sodium balance, as well as negative calcium and magnesium balance.37 Thus, low-salt diets may predispose to calcium and magnesium deficiency and all the negative consequences that come with it (including osteoporosis, hypertension, cardiovascular events, arrhythmias, coronary vasospasm, sudden death, and more).
Overall, chronic salt restriction has minuses as well as pluses:
Most importantly, a meta-analysis of almost 170 studies noted that sodium restriction only lowers blood pressure by approximately 1%-3% in normotensives and 3.5%-7% in hypertensives98; however, restricting sodium increases aldosterone, renin, noradrenaline, and blood lipids. It is hard to justify dietary sodium restriction when the overall cardiovascular risk seems to worsen rather than improve when all risk factors are taken into account.
Unfortunately, salt restriction is now so much part of conventional wisdom, in a way that goes beyond the evidence, that it hard to know where to get reliable advice about it. But as long as you are avoiding sugar and processed food, it is not clear you need to worry about salt. Of course, you should worry about high blood pressure, but beyond taking blood pressure medication, avoiding sugar and processed food and may do a lot more to reduce your blood pressure than cutting back on salt. Also, I’d like to see a study on the effects of fasting on blood pressure. Blood pressure is easy to measure frequently, so it is possible to find out how your blood pressure responds to avoiding sugar and processed food and to fasting.
For annotated links to other posts on diet and health, see: