Excessive salt in the diet weakens immunity system

Thursday March 26th, 2020

A high-salt diet weakens the immune system, German researchers reported last night.

Research led by the University Hospital Bonn, Germany, found mice that were fed a high-salt diet suffered from severe bacterial infections, while human volunteers who consumed an additional six grams of salt – equivalent to two fast food meals – a day also showed pronounced immune deficiencies.

Professor Dr Christian Kurts from the Institute of Experimental Immunology at the University of Bonn said: "We have now been able to prove for the first time that excessive salt intake also significantly weakens an important arm of the immune system.”

The findings, published in Science Translational Medicine, are described as “unexpected” because other studies have opposite results.

These include a study that found infections with certain skin parasites in laboratory animals healed faster if these consume a high-salt diet because the macrophages eat and digest parasites and are particularly active in the presence of salt.

This led to several physicians believing that sodium chloride has a generally immune-enhancing effect.

Dr Katarzyna Jobin, lead author of the study, who has since transferred to the University of Würzburg, said this latest study demonstrates that this generalisation is not accurate for two reasons.

First, the body keeps the salt concentration in the blood and in the various organs largely constant, otherwise important biological processes would be impaired. The skin is the exception to this rule because it functions as a salt reservoir of the body.

Second, the kidneys have a sodium chloride sensor that activates the salt excretion function. But this can cause glucocorticoids to accumulate in the body, which inhibit the function of granulocytes.

Dr Jobin said granulocytes, like macrophages, are scavenger cells, but they do not attack parasites. Instead they target but mainly bacteria.

If they do not do this to a sufficient degree, infections proceed much more severely.

“We were able to show this in mice with a listeria infection,” she said. “We had previously put some of them on a high-salt diet. In the spleen and liver of these animals we counted 100 to 1,000 times the number of disease-causing pathogens.”

In human volunteers, who consumed six grams of salt in addition to their daily intake for a week, it was found their immune cells coped much worse with bacteria after the participants had started to eat a high-salt diet.

The excessive salt intake also resulted in increased glucocorticoid levels.

“Only through investigations in an entire organism were we able to uncover the complex control circuits that lead from salt intake to this immunodeficiency,” said Dr Kurt. “Our work therefore also illustrates the limitations of experiments purely with cell cultures.”

Jobin K, Stumpf NE, Schwab S et al. A high-salt diet compromises antibacterial neutrophil responses through hormonal perturbation. Science Translational Medicine 25 March 2020

https://stm.sciencemag.org/lookup/doi/10.1126/scitranslmed.aay3850

Tags: Diet & Food | Europe | General Health

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