This article is from the WebMD Feature Archive

The condition is also called 'water intoxication' because it can result from an excessive intake of plain water.

Lead author Dale B. Speedy, MBChB, and his colleagues write about a 35-year-old athlete whose sodium dipped to dangerously low levels after he completed an Ironman triathlon.

This type of race consists of a 2.4-mile swim, a 112-mile cycling course, and a 26.2-mile run. The man finished the race in 14 hours and three minutes, then collapsed with seizures just outside the medical tent. He weighed about seven pounds (approximately 5% of his body weight) more after finishing the race. Experts estimated that he drank about 23 liters during the competition.

Once the medics got his seizures under control he was transferred to the emergency department at the local hospital. For the next two days he had seizures, but he began to improve on the third day. By the eighth day he was well enough to go home. Speedy and his co-authors write that many other competitors in the same race also developed low blood sodium, but not as severely as this patient.

The authors emphasize that the patient drank "excessive" amounts of fluid -- averaging approximately 1.64 liters per hour throughout the event. They suggest that drinking fewer fluids overall, and drinking fluids that have sodium such as many sports drinks, could have prevented the man's severe condition.

"Most emergency physicians assume a runner or a cyclist who gets a little goofy is dehydrated and needs more water or [sugar], but in the process you can treat them to death," says Carl Foster, PhD. "If you leave them alone their kidneys will sort things out."

Foster, a professor of exercise and sports physiology at the University of Wisconsin in La Crosse, tells WebMD that it's not always easy to know if your sodium is getting too low. "Like many other intoxicating states, you may not realize you're there," he says. Impaired athletic performance, such as slowing down, could be a signal that water intoxication is setting in. "If you are going to be participating in an event in which you anticipate a large fluid loss, take fluid-replacement products that have sodium," he warns.

"We often see mild hyponatremia in long-distance runners and triathletes," says Nancy Auer, MD, vice president of medical affairs at Swedish Medical Center in Seattle. "These individuals probably need to consume a little more salt, but it should be diluted." Auer, the former president of the American College of Emergency Physicians, recommends drinking diluted Gatorade or similar products during long-distance events, especially in hot weather.

"I think the take-home message is that the pendulum has swung, from electrolyte solutions [like Gatorade] to plain water. Maybe we need to make sure there is more sodium in the beverages we're encouraging these athletes to drink," says Auer. As for the "conventional wisdom" behind the handouts of free water at athletic events, she tells WebMD, "that wisdom may not be the best wisdom."

• Athletes who participate in extreme events like triathalons may drink excessive amounts of water while they compete. But in trying to avoid dehydration, these athletes can deplete their blood sodium levels so much that they can develop a potentially fatal condition called hyponatremia.
• Researchers from New Zealand report one triathlete with hyponatremia had seizures for days after he drank about six gallons (23 liters) of water during competition.
• Experts note those who participate in such extreme events should consume some salt diluted in water or drink sports drinks in order to prevent hyponatremia.

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