Common salt was once so precious that only the rich could help themselves at the table – poorer people sat ‘below the salt’. But our love of salt is probably explained by the two chemicals it contains, sodium and chloride ions – both are essential for normal body function.
Why we need salt
Sodium and chloride ions are found in every body cell and fluid – our muscles, nerve cells, hearts, digestive organs and other tissues are activated by “sodium pumps”, which move sodium in and out as required.
We need a daily top-up from food and drink, to replace sodium lost in sweat, body secretions, and urine; our brains, kidneys and hormones constantly monitor and adjust sodium levels throughout the body to keep them within safe limits. We pass more salt and water in urine if levels are high, and less salt in sweat when we acclimatise to hot weather.
Salt can be poisonous, so don’t use a salty drink to make someone vomit. We feel thirsty when sodium levels rise, and drink extra fluid to help our kidneys excrete surplus salt. But if our safety mechanisms can’t keep up, our nerves and muscles malfunction; this can lead to confusion, convulsions and, if left untreated, death.
Some medical conditions and drugs increase sodium levels – for example, dehydration (including during extreme exercise), some forms of diabetes, kidney disease, and diuretics (“water pills”).
In the longer-term, excess salt can trigger fluid retention, raised blood pressure, ankle swelling, or heart failure. People whose diets contain a lot of salt are more likely to develop raised blood pressure, and complications such as heart attacks and strokes.