Tuesday, March 27, 2012

The Hidden Dangers of Drinking Too Much Water

Like many marathon runners, Kate Mori always drank plenty of fluids before, during and after a race, rather than waiting until she got thirsty.

"I'd always been taught you had to 'stay ahead' of thirst and that being thirsty was a sign you were already dehydrated," says the 42-year-old sports scientist. In 2007, Mori took part in the London Marathon - her fourth, and the hottest on recos peaking at 23.5C. Conscious of the repeated advice to maintain fluid intake coming over the PA system, she took frequent drinks at the water stations along the route.

By the 18th mile, Mori felt "quite poorly" but was determined to finish; she was raising funds for a children's cancer charity and wanted to ensure they got their sponsorship money. Near the end, she needed help from other runners to stay upright; hours later she was in casualty at the Royal London Hospital in Whitechapel, suffering from severe diarrhoea, vomiting and increasing confusion, with her legs endlessly mimicking a running motion. "I thought I was still in the marathon," she says.

Mori was not dehydrated from drinking too little fluid, as might be at first assumed. She had drunk too much. As a result she had developed a dangerous but little-recognised condition called exercise-associated hyponatraemia (EAH). Sometimes called water intoxication, EAH is marked by a low blood sodium concentration and can cause the brain to swell, causing confusion, loss of consciousness and seizures.

Mori made a full recovery after intravenous treatment with sodium chloride to redress the low concentration of sodium in her blood. Another contestant in that year's marathon was not so fortunate. David Rogers, a 22-year-old fitness instructor, died of EAH after finishing the race in three hours 30 minutes.

Mori isn't sure how much she drank during the race. "But the consultant reckoned it was probably about three litres of water," she says. "Ironically, at the finish I was taken into a first aid tent and offered more water.

"I feel ashamed that with my job [she teaches an MA in sports development at Gloucestershire University] I did not have the awareness about this condition," she adds. "It is far more dangerous than dehydration."

With the 2012 London Marathon taking place next month, most would-be runners will be similarly advised on the need to avoid dehydration, especially if temperatures rise. Dehydration occurs when the body's normal water content is reduced and its balance of salts and sugar upset. But according to many medical experts, thousands of runners could be risking their health if not their lives by drinking too much rather than too little.

Timothy Noakes, professor of exercise and sports science at the University of Cape Town, South Africa, who has spent the last 30 years researching the topic, says that the dangers of dehydration during endurance exercise have been exaggerated, with the result that cases of EAH are on the rise. He says runners need to be warned that overconsumption of fluids (whether water or sports drinks) before, during, or after exercise can have a potentially fatal outcome. 

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