Electrolytes

How it works

Sweat contains water and electrolytes, mainly sodium, with smaller amounts of chloride, potassium, calcium and magnesium. Sodium helps the body retain fluid, stimulates thirst and supports nerve and muscle function. During long or hot sessions, large sweat losses can lead to dehydration, while drinking only plain water in very large amounts can dilute blood sodium, a dangerous condition called exercise-associated hyponatraemia. Adding sodium to drinks improves fluid retention and helps maintain blood sodium. Sweat sodium concentration differs greatly between individuals.

What research supports

• Improves fluid retention during rehydration after exercise compared with plain water
• Helps maintain blood sodium during prolonged exercise with heavy sweating
• May reduce the risk of exercise-associated hyponatraemia when combined with sensible drinking
• Can help maintain hydration and performance in hot conditions
• Evidence that electrolytes prevent muscle cramps is limited and mixed

Dosage

Typical guidance for prolonged or heavy-sweat exercise: about 300–600 mg sodium per hour, sometimes more for very salty sweaters, with fluid intake guided by thirst and sweat rate (often 400–800 mL per hour). After exercise, drinking about 1.25–1.5 L of fluid per kg of body weight lost, with sodium, supports rehydration.

Timing

Use electrolytes during sessions longer than about 60–90 minutes, in hot or humid conditions, or when sweat losses are high. They can also be used after training to rehydrate, or before exercise in the heat. Weighing yourself before and after training helps estimate sweat losses; around 1 kg lost is roughly 1 litre of sweat.

Side effects

• Stomach upset with very concentrated products
• Excess sodium intake if used routinely when not needed

Food sources

Table salt, Salty snacks such as pretzels, Broth and soups, Milk (sodium, potassium, calcium), Bananas and potatoes (potassium), Coconut water (potassium, low sodium).