Reduced‑osmolarity ORS

Reduced‑osmolarity ORS is an oral rehydration solution with a lower concentration of glucose and sodium than the original World Health Organization formula.

Composition and rationale

Oral rehydration therapy treats dehydration by providing water, glucose and electrolytes in proportions that maximize absorption. The classic WHO formula had an osmolarity of around 311 mOsm/L. In 2003 WHO and UNICEF introduced a reduced‑osmolarity formulation with a total osmolarity of about 245 mOsm/L. This solution contains 75 mmol/L of sodium, 75 mmol/L of glucose, 20 mmol/L of potassium, 65 mmol/L of chloride and 10 mmol/L of citrate. Lowering the osmolarity reduces the risk of hypernatremia and decreases stool output and vomiting compared with the standard solution. The glucose concentration remains high enough to drive sodium absorption via the sodium–glucose co‑transport mechanism in the small intestine. Reduced‑osmolarity ORS has saved millions of lives by making it easier to treat cholera and pediatric diarrhea without intravenous fluids.

Benefits for athletes and hydration

The same principles that make reduced‑osmolarity ORS effective in medical settings apply to sports hydration. Drinks with lower osmolarity empty from the stomach faster and enter the intestine more quickly than highly concentrated beverages. When athletes consume high‑sugar drinks, the osmotic load can draw water into the gut and cause bloating or diarrhea. Using a reduced‑osmolarity mixture of glucose and electrolytes promotes rapid water uptake and minimizes gastrointestinal distress. Athletes mixing their own sports drinks can approximate reduced‑osmolarity ORS by combining about 3–4 % carbohydrate with sodium, potassium and citrate salts. Because sodium losses in sweat are lower than in severe diarrhea, the exact composition can vary, but the goal is to keep osmolarity well below that of the blood.

Reduced‑osmolarity ORS demonstrates that a balanced combination of glucose and electrolytes can rehydrate effectively without overwhelming the gut. This concept underpins many modern sports drinks designed for sustained endurance exercise.

Related Terms: WHO sodium target (ORS), Glucose–sodium co‑transport, Trisodium citrate (ORS), Dilution ratio, Custom blend