On the other hand, surplus salt can help the body to fight off infections, according to a new study that has added fuel to the debate over salt's minuses and merits.
Never before has salt consumption been discussed so intensively, noted Karl-Ludwig Resch, managing director of the German Institute for Health Research and a specialist in physical medicine and rehabilitation. "Ten years ago, salt intake was basically an academic topic. Now it comes up on television every few days," he said.
The findings of studies on the essential mineral, known chemically as sodium chloride (NaCl), are seldom as clear as many people would like. Resch said scientists passionately - and not always objectively - debated salt's effects until at some point they became "blind to other arguments."
What's known for certain is that we've got a long way to go before we figure out salt, a valuable commodity in earlier centuries and important for the body's fluid balance, bone formation, nervous system and digestion. Add the immune system to the list, says a team of German and American researchers.
It was already known that the body stores surplus sodium in the skin. But why? Writing in the US-based scientific journal Cell Metabolism, the researchers said that sodium ions (Na+) accumulated at the site of bacterial skin infections in humans and mice. And they showed that the sodium bolstered the mice's immune defence.
"The salt stores enable the skin to protect itself against microbes," said Jonathan Jantsch, a professor at Regensburg University Hospital's Institute for Clinical Microbiology and Hygiene and the study's lead author. They do so, according to the researchers, by activating immune cells called macrophages, which kill infectious agents.
The findings shouldn't be seen as carte blanche for unbridled salt consumption, though, Jantsch warned. "Those who ingest too much salt are still at risk of developing cardiac or vascular conditions," he said, adding that the study had cast new light on the maligned mineral nonetheless.
Salt's importance in all sorts of body functions is undisputed. A person couldn't survive without it - the fluid and nutrient balance in the body's cells would be disrupted, as would the body's metabolism. This is why everyone has about 200 grams of salt in his or her body, which can be tasted, for example, in sweat and tears.
Its indispensability for living creatures can be seen in animal behaviour.
"Sodium is the only substance that animals sense a deficiency of and then try to remedy," pointed out Hubert Spiekers, director of the Institute for Animal Nutrition and Feed Management at the Bavarian State Research Centre for Agriculture. If an animal lacks salt, it eats soil or bites into wood. Salt is added to livestock feed or provided in the form of a salt lick.