Rationale for upper limits of electrolyte replacement during exercise.

The addition of carbohydrate and sodium to sport drinks has been recommended to enhance fluid intake and absorption and to delay fatigue. Other electrolytes (E) which are lost through sweating are also commonly added. However, too many E may lead to increased serum E and osmolality levels, which may negatively influence thermoregulation, depress sweating, and cause gastrointestinal distress. On the other hand, drinking large amounts of plain water to compensate sweat loss may induce hyponatremia. Therefore, literature describing sweat E losses was examined in order to estimate average whole-body E loss and to determine an upper limit for replacement of E with sport drinks. Mean E loss was determined from 13 studies, with +/- 1 SD resulting in a hypothetical range for E losses. Correction for net absorption resulted in an upper limit fo electrolyte replacement. It is suggested that the E levels in sport rehydration drinks should not exceed the upper limit of the range given.