It’s been considered conventional wisdom for decades that sodium (half of table salt, which is sodium chloride) raises blood pressure. All else being equal, water does generally follow sodium in order to maintain osmotic balance, keeping concentrations of solutes in one body compartment similar to those in another.
But is it really this simple inside our bodies?
The Blood Pressure Regulatory Hormones
The answer is, not usually, or at least not always. The reason is because the body needs adequate sodium for many physiologic processes, and it has a complicated system for hanging on to it when the intake is low. The system involves several hormones: renin (released in response to low blood volume), which then activates angiotensin II, which both causes blood vessels to constrict and also triggers release of aldosterone and antidiuretic hormone (ADH). The former retains salt while excreting sodium, while the latter maintains fluid volume generally. Like most systems in the body, there are buffers and feedback mechanisms, checks and balances to keep everything in homeostasis, or balance.
What this means is, even though metabolic panels (CMP) will check sodium and chloride, you can’t necessarily conclude that you’re getting the right amount of salt just because your levels are in range. That just means the system is working, but it’s possible that it might have to work really hard in order to keep that balance.
All that extra work comes with a cost.
Salt, Blood Pressure, Renin, and Aldosterone
Some people are considered “salt sensitive” relative to the rest of the population. These people are those whose blood pressure rises at least 5 mmHg with higher salt intake. Those whose blood pressure rises less than 5 mmHg with higher salt intake are considered salt resistant. Then there are some who have a paradoxical reaction, and their blood pressure falls in response to salt (there’s always at least someone who has an opposite reaction to everything, I’ve found!) Notice, though, these blood pressure changes aren’t huge either way—and in this study, only 18.4% of study participants are considered salt sensitive, while 81.6% are either salt resistant or have a paradoxical reaction.
In this study, meanwhile, salt restriction had no significant effect on blood pressure at all.
This study also shows that reduced sodium intake led to only a slight reduction in blood pressure, but renin and aldosterone levels went up more than 3-fold, proportional to the degree of sodium restriction.
This study likewise showed that renin and aldosterone rise proportional to sodium restriction. This is a problem, because aldosterone increases arterial stiffness, as does renin.
Salt Restriction Worsens Risk of Cardiovascular Disease
Perhaps because of the effects on renin and aldosterone at least in part, salt restriction as been associated with increased cardiovascular morbidity and mortality, including heart attack risk. This is particularly true in those without hypertension, though it is true in those with hypertension as well.
The increased risk may also be because, in addition to the renin and aldosterone effects, low sodium intake triggers increased levels of norepinephrine (a precursor to epinephrine, or adrenaline—the primary neurotransmitter associated with the sympathetic, “fight-or-flight” nervous system), and also tends to spike insulin (more on this in a future article). Insulin resistance is of course part of the metabolic syndrome picture, which includes obesity, hypertension, eventual diabetes, and heart disease risk due to elevated glucose.
What’s the Alternative?
According to Dr James DiNicolantonio in “The Salt Fix,” across the globe, when no restrictions are applied, people consistently consume between 3 and 6 grams of salt per day. The healthy set point for most seems to fall in that range, in contrast to the RDA recommendation of 2300 mg per day for healthy individuals, or 1500 mg per day for those with hypertension.
This study indeed shows the those who consume between 3 and 6 grams per day (or around 1-3 teaspoons per day) had a lower overall risk of cardiovascular events.
One caveat here: highly processed foods, which is nearly anything boxed, bagged, canned, or in a wrapper, tend to be quite high in sodium. For those who are salt sensitive, it would be best to avoid these—but then, highly processed foods full of fake chemicals and lots of sugar are terrible for everyone. Instead, choose whole, unprocessed foods, with half your plate veggies at every meal, and liberally use iodized sea salt or Himalayan salt to taste at every meal. And if you drink water stripped of minerals or sweat heavily, you’ll likely need to add even more!