Effect of Dilution of Sports Drink on Water Balance and Beverage Preference of Heat-Exposed Steel Workers

Eight skilled workers engaged in heat-exposed work in front of a blast furnace in a steel factory were asked to drink a sports drink or one of its dilutions of x 2, x 3, or x 5 during a regular daytime shift in the summer of 1999. A regular lunch was taken and the examined beverage was iced and was allowed to be consumed ad libitum. The beverage was changed each day during four days of the experiment without informing the dilution ratio. The non-diluted beverage contained 21mEq/ℓ of Na+, 5mEq/ℓ of K+, 6.7g/dl of carbohydrate. In average, the body temperature measured in the ear canal was elevated by 0.34℃, the loss of body weight was 1.77kg, total beverage intake was 1,875g, total amount of urine was 291g, and the total water loss was 3,732g (1,350〜5,810g) during a single shift. Twenty out of 24 cases experienced more than 1.5% of weight reduction during morning work without noticing any subjective symptoms of dehydration. The amount of weight loss during morning work was significantly smaller when x 2 or x 3 dilution was taken compared to a non-diluted beverage. The mean value of urinary Na+ concentration was decreased after 8 hours of work; however, the difference was not significant. The urinary K+ concentration was significantly increased. When the total amount of urinary sodium excretion in stored urine was calculated, the x 3 dilution recorded the largest amount. Regarding palatability, the x 2 dilution received the best evaluation, whereas all subjects felt the original beverage as too condensed. We did not observe any adverse effect from diluting the sports drink for x 2 or x 3, when supplying them as water and electrolyte replacements for dehydrated steel workers.