Prior to 1969 athletes were advised to avoid drinking during exercise. But beginning in the 1970's, the idea gained credence that not to drink during exercise was “criminal folly” that could lead to dehydration-induced heat stroke. As a result athletes were advised to drink “beyond thirst” by ingesting “as much as tolerable” during exercise. The immediate consequence of this new advice was first identified in 1981 when a female runner developed exercise-associated hyponatremic encephalopathy (EAHE) during a 90km ultramarathon foot race in South Africa.

In 1991 we provided definitive evidence that EAHE is due to abnormal fluid retention in those who overdrink during prolonged exercise and to which a sodium deficit plays little or no part. Shortly after the publication of this compelling evidence, influential sporting organizations such as the American College of Sports Medicine (ACSM) and the National Athletic Trainers Association (NATA), both of which receive funding from the sports drink industry in the United States of America (USA), began to promote the value of drinking “beyond thirst” and “as much as tolerable”. But these guidelines failed to warn of the proven dangers of overdrinking during exercise. As a result, more than 12 documented deaths from EAHE and in excess of 1000 cases of exercise-associated hyponatraemia (EAH), all entirely preventable, have been reported in the scientific literature since 1991.

Prevention of both conditions requires (i) that athletes be taught to drink according to the dictates of thirst before, during and after exercise; (ii) that physicians treating collapsed athletes with an altered level of consciousness do not infuse any fluids intravenously until a diagnosis of EAHE has been excluded; and (iii) that only hypertonic (3% or greater) saline solutions be used to treat patients with EAHE. The adoption of these guidelines has minimized the incidence of both EAH and EAHE in New Zealand and South Africa. This approach should be adopted also in Europe and the USA if these entirely preventable conditions are to be eradicated.