Sodium / Electrolytes

Human RCT Supplementsperformance recovery Last reviewed 2026-09-28

Summary

Sodium is the main electrolyte lost in sweat. Research supports sodium-containing fluids for better fluid retention and rehydration, and sodium preloading before exercise in the heat to expand plasma volume; exercise-associated hyponatremia is mainly a problem of drinking too much plain water.

Mechanism

Sodium is the dominant extracellular electrolyte. It stimulates thirst, promotes renal water retention, and drives sodium-glucose co-transport that speeds intestinal water absorption. Taking sodium with fluid before exercise in the heat expands plasma volume, offsetting early sweat losses; during and after prolonged sweating, replacing sodium helps hold onto ingested fluid instead of losing it as urine.

Reported effects

Ratings are relative to peers in the same category, not absolute claims.

Fluid retention after drinking★★★☆☆Sodium-containing beverages are retained better than water in the first hours.

Pre-exercise plasma volume expansion★★☆☆☆Sodium plus fluid before exercise in the heat expands plasma volume; effects on performance are modest.

Reducing hyponatremia risk★★★☆☆Sodium-containing fluids reduce the risk seen when drinking large volumes of plain water during long events.

Studied dosing: research context

ACSM guidance advises sodium-containing beverages during and after prolonged exercise and eating salty foods. Sodium preloading protocols in the literature typically provide 20-40 mg of sodium per kg of body mass with 1-2 liters of fluid 1-2 hours before exercise in the heat. Typical sports drinks contain 20-30 mmol/L sodium. These are protocols used in research, not guidance.

Research context only. This is not a recommendation.

Safety

Sodium intake interacts with blood pressure in salt-sensitive individuals. The main danger described in the literature is dilutional hyponatremia from overdrinking plain water during long events, which can be fatal; the ACSM position stand advises drinking to thirst rather than forcing fluids. Sodium preloading is intended for planned heat-exercise scenarios, not routine daily use.

Limitations

The beverage hydration index was measured in resting, euhydrated adults and may not reflect rehydration during or after exercise. Optimal preloading dose and timing are not standardized, and benefits apply mainly to prolonged exercise in heat rather than short workouts.