Water and electrolyte replacement during repeated days of work in the heat.

In an attempt to determine the value of replacing sweat losses with and electrolyte solution, 12 subjects (2 women and 10 men) were dehydrated (minus 3% body weight) on 5 successive days. During one 5-d sequence, the subjects replaced fluid losses with a glucose-electrolyte solution, while water was the only fluid ingested during a second 5-d series. With the exception of the drink, daily ionic and caloric intakes were identical for the two 5-d conditions. Measurements of water and electrolyte losses in sweat and urine showed a positive balance in body Na+, K+, and Cl- during both the water (W) and electrolyte solution (ES) treatments. Subjects accumulated significantly more Na+ during the W experiments (392 mEq/5 d) than when the electrolyte solution was ingested (334 mEq/5 d). As a result, the extracellular fluid compartment, represented by plasma volume, increased 12.2 and 9.0% during the 5-d sequence of the W and ES trials, respectively. It was concluded that the addition of electrolytes to drinking water is of minimal value for subjects who dehydrated (-3%) on repeated days and are permitted to ingest food and drink libitum