Glucose–sodium co‑transport

Glucose–sodium co‑transport is the process by which glucose and sodium ions are absorbed together across the intestinal wall, promoting water uptake.

Physiological basis

In the small intestine, epithelial cells contain a transporter called SGLT1 that moves glucose and sodium from the lumen into the cell. For every molecule of glucose taken up, a sodium ion accompanies it. This coupling means that sodium absorption does not stop even during severe diarrhea. When sodium and glucose enter the cell together, water follows osmotically, allowing rapid rehydration. This mechanism underlies oral rehydration therapy and explains why simple solutions of glucose and sodium can treat dehydration. The co‑transport process saturates at high sugar concentrations; excess sugar draws water into the gut and may slow gastric emptying. Maintaining the right ratio of glucose and sodium – roughly equimolar concentrations as used in low‑osmolarity ORS – maximizes uptake. Potassium and citrate in the solution help replace additional electrolytes and correct acidosis.

Relevance to sports hydration

During prolonged exercise, athletes lose water and electrolytes through sweat. Drinking a beverage that contains both glucose and sodium leverages the co‑transport mechanism to speed fluid absorption. Many sports drinks use around 4–8 % carbohydrate and include sodium to balance flavour and effectiveness. If the drink is too concentrated in sugar without enough sodium, absorption slows and stomach discomfort may occur. Conversely, very low carbohydrate drinks may not supply enough fuel for endurance performance. Athletes can mix their own drinks using powders or sachets to match the desired carbohydrate and sodium content. Understanding glucose–sodium co‑transport helps athletes appreciate why a balanced mix of sugar and salt can hydrate more quickly than water alone.

By relying on the body’s built‑in transporters, glucose–sodium co‑transport forms the scientific foundation for effective oral rehydration solutions and many sports drinks.

Related Terms: Reduced‑osmolarity ORS, WHO sodium target (ORS), Trisodium citrate (ORS), Dilution ratio, Custom blend