Hyperhydration Greater Threat to Athletes than Dehydration

Hyperhydration can pose a greater threat to athletes than dehydration, which is rarely the cause of the hypotension associated with mid-competition collapse, an article published in BMJ said.

Most commonly, exercise-associated postural hypotension (a form of vaso-vagal fainting that occurs within minutes after exercise ends) is really to blame when athletes collapse during workouts or competition, wrote Tim Noakes, MD, of the University of Cape Town in South Africa, and in fact, hyperhydration poses more of a threat than dehydration.

"Over the past 40 years humans have been misled ... to believe that they need to drink to stay 'ahead of thirst' to be optimally hydrated," he wrote. "In fact, relatively small increases in total body water can be fatal. “

“There is barely any risk that dehydration can occur in healthy athletes competing in a modern endurance event in which ample fluid is available. Only when the total body water is reduced by about 15%—as occurs in those lost in the desert without water for more than 48 hours—is voluntary motor activity completely inhibited, resulting in paralysis.”

Noakes also cautioned against confusing dehydration-based collapse with sporadic cases of heatstroke, which are not benefited by post-exercise hydration.

“Hydration influences regulation of body temperature in competitive athletes only indirectly. The key determinant of the body temperature during exercise is the exercise intensity or metabolic rate; the greater the intensity, the higher the temperature.”

-Michael Potts