This typically allows a fluid expansion or retention of about 600 mL (above consuming fluid alone) by reducing urinary volume. Glycerol hyperhydration may aid high-intensity endurance exercise in hot and humid environments where sweat losses are high and the opportunities to replace fluid are significantly lower than the rates of fluid loss. However, glycerol hyperhydration has not improved performance in all studies of this type. In addition, the underlying mechanism is not clear because the purported improvements in heat dissipation and decreases in cardiovascular stress have not been observed.
Side effects reported with glycerol hyperhydration include nausea, gastrointestinal distress, and headaches resulting from increased intracranial pressure. Glycerol hyperhydration can also substantially dilute and lower plasma sodium prior to starting exercise and may thus increase the risk of dilutional hyponatremia if the individual drinks too much during exercise. Endurance athletes who want to hyperhydrate with glycerol should be supervised and monitored by appropriate sports medicine professionals. Athletes should use it in competition only after adequate experimentation and fine-tuning.
