Electrolytes: Why Water Alone Is Sometimes Not Enough

What Are Electrolytes?

Electrolytes are minerals that carry an electrical charge when dissolved in fluid. In the body, they are found in blood, urine, and cellular fluid and are essential for nerve impulse transmission, muscle contraction, acid-base balance, and fluid distribution between compartments (intracellular vs extracellular).

The primary electrolytes and their roles:

• Sodium (Na+) — the dominant extracellular electrolyte; governs fluid volume and blood pressure
• Potassium (K+) — the dominant intracellular electrolyte; critical for heart rhythm, nerve conduction, and muscle function
• Magnesium (Mg2+) — cofactor for over 300 enzymatic reactions; involved in muscle relaxation, protein synthesis, and nerve function
• Calcium (Ca2+) — triggers muscle contraction and nerve impulses; also involved in blood clotting
• Chloride (Cl−) — partners with sodium to maintain fluid balance

When Electrolytes Matter Most

For most people in most circumstances, a balanced diet provides adequate electrolytes and plain water covers hydration needs. But electrolyte balance becomes critical in specific contexts:

• Exercise lasting over 60 minutes — sweat contains sodium (typically 500–1,000mg per litre), potassium, and magnesium. Replacing these losses purely with water can dilute plasma sodium, causing hyponatraemia.
• Hot climates or high sweat rates — sweat rates can exceed 2 litres per hour in hot conditions; sodium losses can exceed 3,000mg in a single session
• Low-carbohydrate or ketogenic diets — ketosis reduces renal sodium and potassium reabsorption; electrolyte supplementation is often necessary
• Illness with vomiting or diarrhoea — rapid electrolyte depletion with gastrointestinal losses

Exercise-Associated Hyponatraemia

Perhaps the most underappreciated risk in endurance sport is hyponatraemia — dangerously low blood sodium caused by drinking excessive amounts of water without replacing sodium. It is more common in women, slower athletes (who have more time to drink), and those drinking plain water rather than electrolyte drinks during events lasting over 4 hours.

Symptoms include nausea, headache, confusion, and in severe cases seizures and death. Ironically, it is more dangerous than mild dehydration. The fix is not to drink more water but to consume sodium with fluid.

Practical Electrolyte Strategy

For most people, food provides adequate electrolytes without supplementation. Foods rich in key electrolytes:

• Sodium — table salt, broth, pickles, cheese (easy to get; most people overconsume)
• Potassium — avocados, sweet potatoes, bananas, beans, tomatoes (most people underconsume)
• Magnesium — dark leafy greens, pumpkin seeds, dark chocolate, almonds (widespread insufficiency)

For exercisers, adding a small amount of salt (¼ tsp) to a litre of water or consuming a quality electrolyte drink (without sugar, if desired) during sessions over 60–90 minutes covers most needs without supplements.