Friday 21 April 2006
Too much water a hazard for marathon runners, study finds
Marathon runners should limit the amount they drink during the race or they may risk headache, collapse, confusion, memory loss, vomiting, seizures, and even death from fluid accumulation in the lungs or brain: all from dilution of the salt in the blood resulting from excess water intake during exercise (exercise-associated hyponatraemia or water intoxication). Runners with exercise-associated hyponatraemia or EAH should be treated with hypertonic (sodium rich) fluids instead of traditional isotonic fluids, finds a new study to be published in a forthcoming issue of the Journal of the Royal Society of Medicine.
Dr Dan Tunstall-Pedoe, co-author of the study and Medical Director of the London Marathon, said: "One patient in the study estimated that he drank approximately 13 litres during the five hours he took to complete the marathon which is more than five times the recommended amount. Drinking excessively before, during and after the event can be extremely dangerous".
Guidance published on the London Marathon website and given to runners since these findings advises slower runners, or those taking longer than 3h 30min to complete the event, to drink no more than half a litre of fluid per hour, particularly in cool weather. Faster runners may need as much as a litre of fluid per hour depending on the temperature.
The study, which examined fourteen runners from the 2003 London Marathon who were treated at St Thomas' Hospital for EAH, also found long delays in the onset of the condition for some runners. Of the fourteen patients, eleven had symptoms of confusion but some had finished the race in a normal mental state and then became confused some hours later.
Women are at a higher risk of EAH. While just under a quarter of runners in the 2003 London Marathon were women, females accounted for half the patients in the EAH study. There was no link between EAH and the length of time it took an athlete to complete the event.
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Exercise-associated hyponatraemia after a marathon: caseseries [PDF 95k]
