The study focused on participants in the 2002 Boston Marathon. Based on blood samples and other data gathered from the 488 marathon runners before and after the grueling marathon, it was determined that 13% of them (more than 1 in 8!) showed indications of hyponatremia, a case of water intoxication.
Among three of these, blood sodium levels were so low they risked imminent death.
So, how much water did they drink? In the course of the marathon, the AVERAGE of these 488 marathon runners consumed 3 liters of water.
Many of them actually gained weight during that race, a contest in which one person died of hyponatremia. Subsequent years’ marathons saw 7 cases of the condition in 2003 and 11 in 2004. The article also makes mention of a 2003 London marathon in which 14 runners were hospitalized for hyponatremia. They all lived, but their brains were so bloated that none could remember finishing the marathon!
Drinking more than one loses during a race can decrease the concentration of sodium in the blood which may result in vomiting, seizures, coma and even death.
The International Marathon Medical Directors Association issued a warning in 2001 that urged runners only to drink when they are thirsty, rather than “drinking ahead of their thirst.”