The Science of Oral Rehydration Therapy

Oral rehydration therapy has been heralded as one of the most important medical advances of the 20th century.
— UNICEF and WHO

Diarrhea kills thousands of children every day – more than AIDS, malaria and measles combined[1].  Diarrheal disease is the second leading cause of death in children under 5 years of age around the world.  Globally, there are nearly 1.7 billion cases of diarrheal disease.  It’s both preventable and treatable[2].  Almost 50% of these deaths are due to dehydration and most involve children less than one year of age[3].

 

Treatment of infectious diarrhea is well established.  A mixture of clean water, salt and sugar; Oral Rehydration Therapy (ORT) safely and effectively replaces fluids and electrolytes.  Since the WHO adopted Oral Rehydration Solution (ORS) in 1978 as its primary tool to fight diarrhea, the mortality rate for children suffering from acute diarrhea has fallen from 5 million to 750,000 deaths annually.  With sodium as a primary component of most ORS’s, taste has been the largest barrier to getting children to drink the medicine.

A treatment is not a treatment if nobody wants to take it.
— Eduardo Dolhun MD

Oral rehydration therapy was developed in the 1940s but did not come into common use until the 1970’s. Oral Rehydration Therapy (ORT) is based on the idea of using the body's digestive system as the most effective form of rehydration. While Intravenous Therapy (IVT) introduces salt water directly into the bloodstream, ORT uses a transport system present in the gut wall to draw water naturally into the tissues of the body. This method of hydration has been shown to be 2-3 times faster than IVT, and does not require healthcare professionals to properly administer. 

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The important aspect of Oral Rehydration Solutions (ORS) is the ratio of sodium to glucose. In the digestive tract, the body absorbs one molecule of glucose along with two sodium ions. As the body takes in glucose and sodium from our diet, it increases the ratio of solute (atoms and molecules dissolved in a solvent like water) to water. This increase then leads to a natural flow of water from the digestive tract into the intercellular space through a different kind of protein called an aquaporin.

After following the sodium and glucose into the intercellular space of the small intestinal wall, water then flows directly into the bloodstream through another aquaporin protein named AQP4.

Glucose is transported to the bloodstream by a protein called GLUT1, while sodium is pumped into the blood by a sodium-potassium pump that exchanges 2 potassium ions from the blood for 3 intercellular sodium ions.

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Many sports drinks contain too much glucose, which can speed the dehydration process. Other electrolyte enhanced drinks do not include glucose or sodium, which does not allow the body to utilize this co-transport system, leading to slower hydration. This is the same reason that drinking ORS is a faster hydration method than drinking plain water.


  1. Liu L Johnson HL, Cousens S, PerinJ, ScottS, Lawn JE, Rudan I, Campbell H, Cibulskis R, Li M, Mathers C, Black RE; Child Heath Epidemiology Reference Group of WHO and UNICEF.  Golabal, regional and national cases of child mortality: an updated systematic analysis for 2010 with time trends since 2000.  Lancet. 2012; 379 (9832): 2151-61
  2. Diarrheal Disease, Fact sheet No 330, April 2013, World Health Organization (WHO)
  3. World Health Organization: The Challenge of diarrheal and acute respiratory disease control.  In point of fact No 77.  Geneva: World Health Organization 1996: 1-4.