Potassium

What it does

Potassium is the main positively-charged mineral inside the body's cells, and its partnership with sodium (which sits mainly outside cells) creates the electrical gradients that make life possible. This balance drives the nerve impulses and muscle contractions that let you move, feel and think, and it is what keeps the heart beating in a steady rhythm. Because of this, potassium levels in the blood are kept within a tight range.

One of potassium's most important everyday roles is in blood pressure. It helps relax the walls of blood vessels and promotes the loss of excess sodium in the urine, so a diet rich in potassium tends to counteract the blood-pressure-raising effect of too much salt. Public-health advice to eat more fruit and vegetables is, in part, advice to get more potassium.

Potassium also supports normal fluid balance and works with other minerals in building and maintaining tissues. It is abundant in fruit and vegetables — bananas, potatoes, leafy greens, beans and dried fruit are all rich sources — so diets high in wholefoods are naturally high in potassium. People with kidney problems need to be careful, because when the kidneys cannot regulate it, potassium can build up to dangerous levels; for most people the challenge is getting enough rather than too much.