Last updated: 3 October 2026
Reviewed by Jordan Morley, FA Level 2 Football Coach
Sodium is the electrolyte lost in the highest concentration in sweat (typically 20-80 mmol/L depending on sweat rate and acclimatisation). During exercise lasting more than 60-90 minutes, sodium replacement alongside fluid prevents hyponatraemia (dangerously low blood sodium) — caused by excessive plain water intake that dilutes sodium. Athletes sweating heavily should consume 500-1000mg of sodium per hour in warm conditions. Sports drinks, electrolyte tablets and salt capsules are common sodium sources. Sodium also stimulates thirst and fluid retention, improving rehydration effectiveness.
- Primary electrolyte lost in sweat
- 500-1000mg/hr in hot conditions
- Prevents hyponatraemia from excess plain water
- Stimulates thirst and improves rehydration
In practice
Sodium is the primary electrolyte lost through sweat, and replacing it during prolonged exercise (especially in heat) is important for maintaining fluid balance and preventing hyponatremia — a dangerous dilution of blood sodium that can occur if an athlete drinks large amounts of plain water during very long events without replacing lost sodium alongside it.
FAQ
Why is sodium replacement important during long exercise sessions?
Sodium is the primary electrolyte lost through sweat, and replacing it helps maintain proper fluid balance, supports hydration, and prevents hyponatremia, a dangerous blood sodium dilution risk during very prolonged exercise.
What is hyponatremia and why is it a risk for endurance athletes?
It's a dangerously low blood sodium concentration, which can occur if an athlete drinks excessive plain water during a very long event without replacing the sodium lost through sweat, and can be serious or life-threatening in extreme cases.