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21 October 2015

Too much salt in food can push the immune system out of balance, according to a new study published in the Journal of Clinical Investigation. A team of researchers led by Dr. Katrina Binger, of Baker IDI Heart and Diabetes Institute, have established that increased salt consumption by rodents leads to delayed healing of their wounds because it reduces the activity of protective immune cells. At the same time, they were successful in explaining the mechanism causing this.

Physicians and scientists studying nutrition agree that consuming too much salt in food is unhealthy and that table salt (sodium chloride) can elevate blood pressure. More recently, researchers believe that high salt diets may also play a role in the development of autoimmune diseases, chronic inflammation, as well as cancer. 'However, we still don’t understand the underlying mechanisms causing this response' says Dr Binger. 'And we don’t know how much salt is too much, that is, how much salt we can eat without compromising our health.'

Genetics play an important role in chronic disease, yet the sharp rise in inflammatory diseases as well as autoimmune diseases—in which the immune system mistakenly attacks healthy cells—suggests that environmental factors also contribute to these diseases in a significant way. ‘Western’ eating habits characterised by high fat and salt levels have recently come under suspicion. Of particular concern are foods high in salt such as breakfast cereals, bread and highly processed foods including meats and cheeses, which are consumed on a daily basis.

In recent years, scientists have established that excessive salt in food affects the immune system in diverse ways. In this most recent study, Dr. Binger, together with colleagues Matthias Gebhardt, and Prof. Müller from the Max Delbruck Center for Molecular Medicine in Germany, demonstrate that too much salt in food weakens a specific group of scavenger cells (macrophages) in the immune system. Macrophages are the first responders to infection and are important in warding off a variety of pathogens. A particular type of these cells, known as type 2 macrophages, play a critical role in repairing wounds and combating too much inflammation. In rodents fed a high-salt diet, wound healing was delayed—in part because of the salt-related weakening of these particular scavenger cells.

At the same time, previous studies by this team have shown that proinflammatory cells—that is, cells that cause inflammation—responded positively to a higher salt intake. The overall result of these seemingly contradictory studies is that salt pushes the immune system out of balance by boosting inflammatory cells, and inhibiting cells that stop inflammation, such as type 2 macrophages.

The study contributes to the growing body of evidence about how the immune system reacts to environmental changes, and may offer new targets for better treatment of a number of diseases—especially those that are caused by the immune system getting out of balance.

Commenting on the findings Dr Binger said, 'The clinical implications of this research are that eating too much salt doesn’t just elevate blood pressure—it compromises the balance of the immune system to directly cause chronic diseases. Dietary salt restriction is a neglected therapeutic option, which could now be looked at for a number of different diseases, such as type 2 diabetes, rheumatoid arthritis and multiple sclerosis'.

Dr Binger’s future research at Baker IDI will investigate the role of a high salt intake on diseases such as atherosclerosis and type 2 diabetes.

Journal article: High salt reduces the activation of IL-4– and IL-13–stimulated macrophages


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