Writing in the Clinical Journal of Sport Medicine, the specialists said that "aggressive drinking to prevent dehydration is unnecessary and carries with it greater risk."
"Fluid intake recommendations suggesting that athletes begin to drink fluids before the onset of the sensation of thirst were targeting those exercising in situations where high sweat rates were present and dehydration could evolve rapidly with known medical and performance outcomes," they said. "Unfortunately, this advice fostered the misconception that thirst is a poor guide to fluid replacement in lower sweat rate situations. We believe that this has facilitated individuals choosing to inadvertently adopt overdrinking."
The dangers of overdrinking can be serious and range from lightheadedness, confusion or nausea to cerebral edema in which the brain swells due to excess water. At least 14 athletes — including a woman who died two days after completing the Marine Corps Marathon in 2002 — are believed to have died from drinking too much during exercise in a condition known as exercise-associated hyponatremia or EAH.
When excess fluids build up up in the body the concentration of sodium can drop precipitously and the kidney become overloaded and are unable to excrete the water load. Cells begin to absorb the water. This can lead to swelling all over the body — most seriously in the brain — which can lead to seizures, coma or even death.
The effects are described in a 2013 article in the journal Medicine & Science in Sports & Exercise by Oakland University researcher Tamara Hew-Butler, who is a member of the panel who made the new recommendations on Tuesday. Of the 669 finishers, 18.5 percent were dehydrated and 34.9 percent were overhydrated.
Another study, published in the British Journal of Medicine in 2010 by James Winger, a physician in the Loyola University Health System, found that more than 40 percent of 197 runners surveyed in the Chicago area drank in preset amounts or even drinking all they could hold. Winger has described fatalities due to overdrinking of water during exercise as "essentially 100 percent preventable."
The expert panel recommended treating EAH with a saline solution that is three times more concentrated than the normal saline solution given to patients for rehydration.