Potassium

The main positively charged ion inside your cells, and the counterweight to sodium outside them. That balance is what allows nerves to fire and muscles — including the heart — to contract, which is why the body regulates it so tightly.

The main positive ion inside cells. Sets the electrical gradient that lets nerves fire and muscles — including the heart — contract. Works against sodium to regulate blood pressure and fluid balance.

• Potatoes with skin
• Beans and lentils
• Bananas
• Leafy greens
• Tomato and orange juice
• Yoghurt
• Salmon

3,400 mg (men) · 2,600 mg (women) for most adults. The upper limit, past which harm becomes likely, is None from food.

Reference intakes are population figures. Pregnancy, illness, age and medication all move an individual’s needs, which is one of several reasons this page is information rather than advice.

A sustained shortage has a name here: Hypokalaemia. That is worth pausing on — nutrients whose deficiency earned a name are the ones where the consequences were severe enough, historically, to be described as a disease.

Most at risk: People on loop or thiazide diuretics, prolonged vomiting or diarrhoea, and eating disorders.

Rarely diet alone. Usually losses: diuretics, prolonged vomiting or diarrhoea, and some kidney and adrenal conditions. Low magnesium makes potassium hard to correct until the magnesium is dealt with.

Muscle weakness and cramps, constipation, fatigue, and — if severe — dangerous heart rhythm disturbances.

Every sign here has other, often likelier, explanations. A list of symptoms is a reason to look into something, never a diagnosis.

Serum potassium is a routine blood test and genuinely informative, unlike several others on this list — because the level itself, rather than the store, is what matters clinically.

Potatoes with skin, beans, lentils, leafy greens, bananas, avocado, tomatoes and dried fruit. Most people who eat plenty of vegetables and legumes get enough without thinking about it.

Over-the-counter potassium is deliberately limited in strength, and prescribed potassium is monitored, because too much is more immediately dangerous than too little. Salt substitutes are often potassium chloride, which matters if you take an ACE inhibitor, an ARB or a potassium-sparing diuretic.

From food, essentially none in healthy people — the kidneys excrete the excess. In kidney disease, or with potassium-sparing diuretics and ACE inhibitors, it accumulates and high blood potassium can stop the heart. Potassium supplements are genuinely dangerous in the wrong person.

Interactions: ACE inhibitors, ARBs and potassium-sparing diuretics all raise levels. Do not supplement while on them without medical advice.