Among the guidelines for diets recommended by the WHO, and physicians in general, is the daily intake of salt. Indeed, it is well known that an excess of salt can lead to an increase in blood pressure, leading to hypertension and cardiovascular complications. And recently, researchers have shown that this excess can also lead to a decrease in the efficiency of the immune system for bacterial infections.
Eating too much salt can affect the body’s ability to fight bacterial infections, according to studies in mice and 10 human volunteers. Christian Kurts of Bonn University Hospital in Germany and his team first showed that mice on a high-salt diet were less able to fight kidney infections caused by E. coli and global infections caused by Listeria monocytogenes, a common cause of food poisoning.
Excess salt: it neutralizes the effectiveness of neutrophils against bacteria
” Bacteria caused more damage before the immune system clears them up Says Kurts. Next, the team gave 10 healthy women and men between the ages of 20 and 50 6 additional grams of salt a day in addition to their normal diet, in the form of three tablets a day.
Graph showing the rate of bacteria present in the spleen in case of infection with L. monocytogenes. In black for a low salt diet, and in blue for a high salt diet. Credits: Katarzyna Jobin et al. 2020
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After a week, some of their immune cells, called neutrophils, had a significantly reduced ability to track down and kill bacteria compared to the same tests performed on each individual before taking additional salt. The team did not examine the effect of high salt intake on the body’s ability to fight viral infections.
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Glucocorticoids and urea responsible for lowering the immune system
The World Health Organization recommends not consuming more than 5 grams of salt per day to avoid high blood pressure, which can cause stroke and heart disease. In the UK, people eat an average of 8 grams, which suggests that many eat as much or more than the study volunteers.
Charts showing the levels of hormones and urea in the body for a low-salt diet (black) and a high-salt diet (blue). Credits: Katarzyna Jobin et al. 2020
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The team believes that two mechanisms are involved. First, when we eat a lot of salt, hormones are released so that the body excretes more salt. These include glucocorticoids, which have the side effect of reducing the immune system throughout the body. Second, there is a local effect in the kidneys. Researchers have found that urea builds up in the kidneys when salt levels are high and that urea suppresses neutrophils.
Sources: Science Translational Medicine
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