Electrolytes Explained: Sodium, Potassium, and the Rest

Electrolytes are charged minerals dissolved in body fluid. They run the electrical and osmotic environment of cells: nerve conduction, muscle contraction, fluid balance, and pH regulation all depend on stable electrolyte concentrations. The body defends those concentrations tightly, mostly through the kidneys. Day-to-day, in most healthy people, you do not need to think about electrolytes. The exceptions — heavy sweat, illness, very low-carb diets, certain medications — are worth knowing.

What each one does

• Sodium: regulates extracellular fluid volume and blood pressure; the dominant electrolyte in sweat.
• Potassium: regulates intracellular fluid; works opposite to sodium for blood-pressure control.
• Chloride: pairs with sodium; rarely a deficiency concern in isolation.
• Calcium: muscle and nerve function plus bone structure.
• Magnesium: enzymatic cofactor in hundreds of reactions including ATP production.

How sweat changes the picture

A typical adult loses about 1 L of sweat per hour at moderate exercise intensity in moderate heat, with sodium losses of around 800–1,500 mg per litre depending on individual sweat rate and 'salty sweater' phenotype. Potassium loss in sweat is much smaller — typically 100–250 mg per litre. This is why sodium dominates the electrolyte conversation in sport.

For most exercise sessions under 60–90 minutes in temperate conditions, you do not net-lose enough sodium to need a replacement drink. Water is enough; the electrolytes in your next meal restore balance. Where it matters is endurance events lasting hours, training in heat, or high-sweat-rate individuals (some lose 2 L/hour) where sodium loss can exceed several grams per session.

When electrolyte drinks help

• Endurance sessions over 90 minutes, especially in heat.
• Multi-day events or training camps where chronic underspending compounds.
• Acute illness with vomiting or diarrhoea — ORS is the gold standard here.
• Very low-carb or strict ketogenic diets, which increase urinary sodium loss.
• Some medications (diuretics, certain antihypertensives) under clinician guidance.

Reading the label

If you are reaching for an electrolyte drink to support a long endurance effort, prioritise sodium content. Many flavoured products on the supermarket shelf have less sodium than a slice of bread, which is fine for taste but misleading if you need real replacement. For acute illness, the WHO ORS ratio is the right target.

What about hyponatraemia?

Exercise-associated hyponatraemia — dangerously low blood sodium from drinking too much plain water during long efforts — is rare but serious. It is most common in marathon runners, ultra-endurance athletes, and people who drink to a fixed schedule rather than to thirst. The current consensus from sports medicine is to drink to thirst during endurance events and include sodium in fluid replacement once efforts pass roughly 90 minutes in warm conditions.

Daily food does most of the work

Sodium is rarely a deficiency in modern diets — most adults consume more than they need. Potassium is the opposite; the average intake in Western populations falls short of the 3,400–4,700 mg/day suggested by major guidelines. Beans, leafy greens, potatoes, bananas, yoghurt, and tomatoes are the easy wins. People aiming to balance blood pressure with food usually benefit more from raising potassium than from dramatically cutting sodium.