Effect of Beverage Temperature and Composition on Fluid Retention After Mild Dehydration

Beverages containing electrolytes promote plasma volume recovery after dehydration by reducing urinary fluid losses. Whether beverage temperature influences urine output during recovery from mild dehydration is not known. PURPOSE: To determine whether urine output, and consequently plasma volume recovery, is affected by changing the beverage temperature and composition of rehydration beverages. METHODS: Ten healthy men age 24±3y (mean±SD) rehydrated for 2 h after thermal/ exercise induced dehydration with one of 4 experimental beverages that differed by solute concentration (water, W or carbohydrate/electrolyte beverage, CE) and temperature (∼4C, C or ∼25C, W). During the first 60 min of rehydration, 175 g of the experimental beverage was ingested every 20 min and during the last 60 min, water was ingested every 20 min at the same temperature as the experimental beverage. Water in the last 60 min was adjusted so 100% of the fluid lost during dehydration was replaced. Blood samples were collected before dehydration and rehydration and every 20 min during rehydration. A urine sample was collected before dehydration and total urine volumes were measured and anayzed before rehydration, after rehydration, and 2 hours after rehydration. RESULTS: Percent dehydration was similar for all four trials (−2.2±0.3, −2.2±0.3, −2.2±0.4, and −2.1±0.3 for W/W, W/CE, C/W, and C/CE, resp; p = 0.99, Temp/Comp). Although fluid mass ingested during rehydation was similar between trials (p = 0.53), urine output showed a trend for an independent effect of temperature with cold beverages producing less urine (p = 0.07) even after correcting for body weight (10.1±3.6 vs. 9.0±3.7 ml/kg body weight; p = 0.08). Although not significant, urine volumes were higher at both temperatures after ingesting CE (764±286 and 702±1 27 vs. 728±192 and 611±311 ml for W/CE and C/CE vs. W/W and C/W resp). Percent retention of ingested fluids immediately and 2h after rehydration were not different by trial (p = 0.71 and 0.28, resp). A trial by time interaction was observed for urine specific gravity and osmolality (p = 0.005 and 0.007, resp), but none of the trials differed by trial at any time point. Urine electrolytes were not affected by beverage temperature or composition. Recovery of plasma volume, heart rate, blood pressure, rectal temperature, and rating of thirst following dehydration were not different by experimental beverage. CONCLUSIONS: Cold beverages may decrease urine output during 2 hours of recovery (ES = 0.4), but the rate of plasma volume restoration was not affected by beverage temperature or composition. Funded by Gatorade Sports Science Institute and Betty Keenan Fund, ISU