Sodium

Essential, and for almost everyone in a Western diet, over-supplied. It regulates fluid balance and blood pressure, and the practical question is nearly always how to have less of it rather than more.

The main positive ion outside cells. Governs fluid balance, blood volume and blood pressure, and is needed for nerve transmission.

• Table salt
• Bread and processed foods — where most intake actually comes from
• Cured meats
• Cheese
• Sauces and stock

1,500 mg adequate intake for most adults. The upper limit, past which harm becomes likely, is 2,300 mg suggested limit — most people eat well above this.

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: Hyponatraemia. 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: Almost nobody eating normally. Deficiency is a medical situation, not a dietary one.

True deficiency from low intake is rare. Low blood sodium usually reflects too much water relative to sodium: some medications, heart, liver or kidney disease, certain hormonal conditions, and occasionally endurance athletes over-drinking during long events.

Rare from diet. Occurs with prolonged heavy sweating replaced by water alone, some medicines, or drinking excessive water — causing headache, confusion, seizures. Endurance athletes are the classic case.

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

Serum sodium is a standard blood test. A low result is far more often about water balance than about salt intake, which is why it is interpreted alongside kidney function and fluid status rather than diet.

Around three-quarters of intake comes from processed and restaurant food rather than the salt cellar, so reading labels changes more than moving the shaker. Herbs, citrus, vinegar and spice let you cut salt without the food tasting flat.

Not something to supplement outside specific medical or athletic circumstances. Electrolyte drinks are useful for prolonged heavy sweating and unnecessary the rest of the time.

The realistic problem for nearly everyone. High intake raises blood pressure and, over decades, stroke and heart disease risk. Most of it arrives in processed food rather than the salt cellar.