Watching salt intake is an important part of cardiovascular health, and new research points to another reason to watch your consumption: your immune system.
Salt (sodium) and consuming it through table salt (sodium chloride) is part of an important balance of electrolytes within the body. Researchers at the University of Würzburg have uncovered a complex role that salt has to play in the immune system that was previously undetected.
Studies in the past lead to an assumption that eating a high-salt diet was good for the immune system based on results achieved from animal studies with parasitic skin infections. This caused scientists to believe that the stimulation of the immune system cells which attack (called macrophages) was enhanced through high-salt diets and predisposed scientists towards endorsing salt because of its ability to enhance the immune system.
We now know, through this year’s study in March, that this conclusion is false. Scientists failed to acknowledge that salt does work well in skin-related biological processes, which is why the skin infections showed an improvement. Salt is held in reserve in skin. However, the extra salt that is consumed doesn’t travel to other parts of the body.
When salt is consumed, the kidneys can detect it because they have a sensor that is sensitive to sodium chloride, and it triggers the kidneys to filter it and excrete it. A secondary effect of the kidneys’ sodium chloride sensor being activated is the cascade of events which follows and disrupts immune system cells.
Glucocorticoids are naturally occurring steroids within the body that are responsible for fighting inflammation. Unfortunately, when the sensor in the kidneys is activated after detecting salt, it causes the glucocorticoids to accumulate. The major problem with the extra glucocorticoids in the body is that they disrupt the functioning of the most common immune cell: the granulocytes.
Granulocytes function similarly to macrophages in that they scavenge and attack foreign invaders and are important parts of the immune system. Instead of attacking parasites like the macrophages as illustrated in the animal studies on salt in the past, granulocytes prefer to attack bacteria.
To test this, scientists fed a high-salt diet to rats infected with the listeria bacteria, and they found that there was between 100-1,000x more bacterial units and pathogens in the rats who were consuming excess salt. They also noted that rats fed a high-salt diet healed more slowly from urinary tract infections.
In humans, researchers added 6 grams of salt to their regular daily intake (5 grams of salt is the current recommendation, which is about 1 teaspoon of salt daily). This additional salt intake was about the same amount you’d find in two fast food “burger and fries” meals. After analyzing their blood for granulocytes, they found that the function of the granulocytes was impaired, and the participants weren’t able to fight off bacterial infections as well after the high-salt experiment.
Additionally, the salt also affected the humans’ glucocorticoid levels as expected, resulting in increased glucocorticoids in the body. This can cause immunodeficiency because, while steroids fight inflammation, they also suppress the immune system.
Salt recommendations and the science behind how it affects the body is changing. If you weren’t already trying to watch your salt intake, maybe knowing that it can make your immune system stronger will give you extra motivation to consume it more consciously.
Instead of seasoning with salt, try a wider variety of spices and herbs. There are many salt-free seasonings available: try adding flavor with the Mrs. Dash line of salt-free seasonings that never leave me wanting to add salt!
Katarzyna Jobin, Natascha E. Stumpf, Sebastian Schwab, et al. A high-salt diet compromises antibacterial neutrophil responses through hormonal perturbation. Science Translational Medicine, 2020 DOI: 10.1126/scitranslmed.aay3850