Tim Noakes, from the University of Cape Town (South Africa) submits that heat-induced dehydration rarely causes athletes to collapse during workouts or competition. In most cases, the culprit is exercise-associated postural hypotension (low blood pressure when standing), in which case primary treatment consists of recovery in a head-down position. Noting that healthy athletes face “barely any risk” of dehydration during competition in an endurance event, the study author states that serious health risks — including inhibition of voluntary motor activity and paralysis — occur only when total body water decreases by 15% or more, which would require 48 hours in the desert with no water. Instead, the author writes that a 2% increase in total body water leads to generalized edema that can impair physical and mental performance. Further increases in overhydration can cause hyponatremic encephalopathy, leading to confusion, seizures, coma, and — if not reversed — death by respiratory arrest. “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,” urges the author, continuing that: “In fact, relatively small increases in total body water can be fatal.”
