The World Health Organization's Oral Rehydration Solution (WHO ORS) has been a cornerstone of global health for decades, effectively combating dehydration from diarrheal diseases, a leading cause of childhood mortality. Its success lies in its carefully balanced, physiological formula, refined over many years of research. Since 2003, the standard formulation has been a reduced-osmolarity ORS, offering improved efficacy and safety over the original formula.
The Scientifically-Backed Composition
The current WHO standard ORS composition is based on the principle of sodium-glucose co-transport, a mechanism that enhances the intestinal absorption of water and electrolytes. The key to its effectiveness is not simply providing water, but delivering specific amounts of glucose and salts that work synergistically to maximize fluid uptake even during active diarrhea. The formula is designed to be hypotonic, or low-osmolarity, with a total osmolarity of 245 mOsm/L, a significant reduction from the original 311 mOsm/L formula.
Key Ingredients and Their Functions
The composition is based on four primary ingredients, carefully measured for a one-liter solution:
- Anhydrous Glucose (13.5g): This sugar is essential for stimulating the absorption of sodium and water in the small intestine through the SGLT-1 co-transporter. This glucose-driven mechanism ensures that hydration can occur even when the intestinal lining is compromised by infection.
- Sodium Chloride (2.6g): Sodium is a critical electrolyte lost during diarrhea and is necessary for many bodily functions. The presence of glucose ensures that this sodium is absorbed efficiently, correcting the sodium deficit caused by fluid loss.
- Potassium Chloride (1.5g): Diarrhea can also cause a significant loss of potassium, another vital electrolyte. Potassium chloride helps replenish these stores, which are crucial for normal nerve and muscle function.
- Trisodium Citrate Dihydrate (2.9g): This compound helps correct the metabolic acidosis that often accompanies severe dehydration, restoring the body's proper acid-base balance. Citrate is also more stable in storage than the bicarbonate used in earlier formulations.
Original vs. Reduced-Osmolarity ORS: A Comparison
The shift to a reduced-osmolarity formula was a major public health advancement. Research showed that a lower concentration of sodium and glucose led to better outcomes for children with non-cholera diarrhea.
| Component (per Liter) | Original WHO ORS | Reduced-Osmolarity WHO ORS |
|---|---|---|
| Anhydrous Glucose | 20.0 g (111 mmol/L) | 13.5 g (75 mmol/L) |
| Sodium Chloride | 3.5 g (90 mmol/L) | 2.6 g (75 mmol/L) |
| Potassium Chloride | 1.5 g (20 mmol/L) | 1.5 g (20 mmol/L) |
| Trisodium Citrate | 2.9 g (10 mmol/L) | 2.9 g (10 mmol/L) |
| Total Osmolarity | 311 mOsm/L | 245 mOsm/L |
The clinical benefits of the reduced-osmolarity formula include reduced stool volume, less vomiting, and a lower need for unscheduled intravenous fluid infusions in children with non-cholera diarrhea. For many adults with cholera, studies have shown that the reduced-osmolarity formula is just as effective as the original, with reduced stool output and vomiting.
The Role of Zinc Supplementation
In addition to the ORS formula, the WHO and UNICEF also recommend a 10 to 14-day course of zinc supplementation for children with diarrhea. Zinc is a crucial micronutrient, and supplementation has been shown to reduce the severity and duration of diarrheal episodes and reduce the risk of re-infection in the months following treatment.
Practical Application and Considerations
For proper use, one sachet of oral rehydration salts is dissolved in one liter of clean water. It is crucial to use the correct amount of water, as using too little can make the solution too concentrated (hyperosmolar), potentially worsening diarrhea. The prepared solution should be used within 24 hours to prevent contamination.
While ORS is a remarkably effective tool, it's not a cure-all. For severe dehydration, particularly in cases of shock or inability to drink, intravenous fluids are required under medical supervision. Furthermore, special care is needed for children with severe acute malnutrition, who may require a specialized ORS like ReSoMal, as their electrolyte needs are different.
Conclusion
The WHO standard ORS composition represents a triumph of evidence-based medicine, offering a simple yet profoundly effective solution to a major global health challenge. The current reduced-osmolarity formula, refined through years of research, provides an optimal balance of glucose and electrolytes to maximize intestinal absorption. Combined with zinc supplementation and continued feeding, it remains the gold standard for treating and preventing dehydration, saving countless lives by making a sophisticated medical treatment accessible and low-tech. For more in-depth information on the history and development of ORT, visit the National Institutes of Health website at https://pmc.ncbi.nlm.nih.gov/articles/PMC11463858/.
