I wrote here on how salt affects blood pressure (or how it doesn’t, as the case may be). As mentioned in that article, low sodium can actually increase the risk for cardiovascular disease by a number of mechanisms. One of those mechanisms is by increasing insulin levels, and thus eventually, insulin resistance.
Here’s a couple of mechanisms for how that happens.
Sodium Restriction Activates Hormones to Retain It
Sodium levels in the body are regulated not just by intake, but also by a delicate balance of hormones. If your intake is too low, the hormones renin, angiotensin, aldosterone, and Antidiuretic Hormone (ADH) step in to increase sodium retention. These hormones themselves are associated with an increase in insulin resistance. This may be because insulin itself stimulates the kidneys to reabsorb sodium, is this may be one mechanism by which the other hormones regulate sodium levels. Because of this effect, ingestion of sugar (which will trigger insulin release) tends to increase sodium retention and thus, blood pressure.
In other words, low sodium leads to higher insulin, and particularly if this is combined with high sugar intake, this leads to higher blood pressure—the exact opposite of what a low sodium diet is supposed to do.
Sodium restriction may occur via limiting intake, via fasting (even intermittent, as electrolytes tend to plunge as ketones rise—this is what causes the “ketogenic flu”), via loss as a side effect of many common medications (including diabetic medications), and also via heavy sweating. All of these could potentially activate the hormones mentioned above, leading to both insulin resistance and increased arterial stiffness.
This study shows that increased exercise training and sweat loss without adequate sodium repletion (somewhere in the neighborhood of 1500 mg of sodium for every half hour of heavy sweating) can lead to symptoms of hyponatremia within two weeks. These symptoms include hypertension, presumably secondary to activation of the renin-angiotensin-aldosterone system. Rehydration with water alone will lead to increased urination, but won’t balance sodium losses.
Sodium Restriction or Loss—> “Fight or Flight”
Salt restriction seems to send an ‘emergency’ signal to the body such that it stimulates the sympathetic, or ‘fight or flight,’ autonomic nervous system. Presumably because the hallmark of this system is to burn energy as rapidly as possible rather than store it (as with the parasympathetic “rest and digest” nervous system), increased sympathetic activity and insulin resistance go hand-in-hand.
Typically, in addition to allowing glucose inside the cells, insulin also has a vasodilating effect on the blood vessels, which should lead to a drop in blood pressure. But this only occurs when the cells of the blood vessels are sensitive to the insulin signal. Low salt diets cause norepinephrine to rise (this is the precursor to epinephrine, otherwise known as adrenaline, the main neurotransmitters of the sympathetic nervous system), and as that occurs, vascular sensitivity to insulin decreases.
This is likely another reason why a low salt diet has less of an effect upon blood pressure than might be anticipated from the osmotic effects of sodium alone. It also demonstrates decreased systemic insulin sensitivity secondary to low sodium levels as well.
Glucose and Salt Together in Salt-Sensitive Individuals
The story is never one-sided, though.
In this study, salt-sensitive individuals seemed to be less able to compensate for high or low salt levels with compensatory mechanisms. These individuals made up 18.4% of those in the study, and they did show an increase in blood pressure of at least 5 mm Hg with high salt intake.
Unfortunately, these individuals are also more likely to be insulin resistant. This will be true even if salt-sensitive individuals consume low salt diets, but it will be significantly worse if they consume high salt diets.
What this means is, if you’re someone whose blood pressure is more sensitive to salt intake, you need to be more careful than most with your sugar and white carbohydrate intake. These are primarily found in processed foods… which also tend to be high in sodium content as well.
Insulin resistance is certainly epidemic. Even those who eat healthy may struggle to keep blood sugar in ideal ranges—and those already committed to eating healthy are more likely than most to follow accepted health guidelines, and limit sodium. For those, increasing healthy salt intake may help to also stabilize blood sugar—particularly if you sweat excessively, are on a low carb or ketogenic diet or an intermittent fasting protocol, are on any medications that deplete sodium, don’t consume much salt, or drink Reverse Osmosis water.