A high-salt diet, which has been linked to an increased risk of heart disease and stroke, can defend the body against invading microbes, according to a new study.
Researchers found that a high-salt diet increased sodium accumulation in the skin of mice, thereby boosting their immune response to a skin-infecting parasite.
"Up to now, salt has been regarded as a detrimental dietary factor; it is clearly known to be detrimental for cardiovascular diseases, and recent studies have implicated a role in worsening autoimmune diseases," said first study author Jonathan Jantsch, a microbiologist at Universitatsklinikum Regensburg and the University of Regensburg in Germany.
"Our current study challenges this one-sided view and suggests that increasing salt accumulation at the site of infections might be an ancient strategy to ward off infections, long before antibiotics were invented," Jantsch said.
Large amounts of sodium stored in the skin, especially in older individuals, can lead to high blood pressure and increase the risk for heart disease and stroke.
"Despite the overwhelming evidence linking dietary salt to disease in humans, the potential evolutionary advantage of storing so much salt in the body has not been clear," said senior study author Jens Titze, who studies the link between sodium metabolism and disease at Vanderbilt University School of Medicine in the US.
A clue to this mystery came when Titze and his collaborators noticed an unusually high amount of sodium in the infected skin of mice that had been bitten by cage mates.
Titze teamed up with Jantsch to examine the link between infection and salt accumulation in the skin. They found that infected areas in patients with bacterial skin infections also showed remarkably high salt accumulation.
Moreover, experiments in mice showed that a high-salt diet boosted the activity of immune cells called macrophages, thereby promoting the healing of feet that were infected with a protozoan parasite called Leishmania major.
The researchers will examine how salt accumulates in the skin and triggers immune responses, and why salt accumulates in the skin of ageing adults.
"A further understanding of the regulatory cascades might not only help to design drugs that specifically enhance local salt deposition and help to combat infectious diseases, but also may lead to novel strategies to mobilise sodium stores in the ageing population and prevent cardiovascular disease," Jantsch said.
"We also think that local application of high-salt-containing wound dressings and the development of other salt-boosting antimicrobial therapies might bear therapeutic potential," Jantsch said.
The study is published in the Cell Press journal Cell Metabolism.
