The urge to chug gallons of water on a hot run can be overwhelming but it's safest only to drink when you truly feel thirsty while exercising, according to a statement published in the Clinical Journal of Sport Medicine.
Overdrinking can lead to severe drops in blood sodium levels during exercise or the following 24 hours, known as exercise-associated hyponatremia or 'water intoxication'. While sufferers initially experience no or mild symptoms, they can develop into vomiting, confusion, headaches or seizures as a result of brain swelling. If not treated immediately, bad cases of water intoxication can be fatal.
The statement urges runners to rely on physiological thirst cues, which can be defined as a "generalized, deep seated feeling of desire for water”, and suggests that they "drink palatable fluids when thirsty" before, during and after exercise.
Stay safe out there!