Effect of drink flavor and NaCl on voluntary drinking and hydration in boys exercising in the heat

This study was intended to assess the influence of drink flavor and composition on voluntary drinking and hydration status in children exercising intermittently at 35 +/- 1 degrees C and 45-50% relative humidity. Twelve boys (9-12 yr) performed three 3-h identical sessions (four 20-min cycling bouts at 50% maximal O-2 uptake followed by 25-min rest). One of three beverages (chilled to 8-10 degrees C) was assigned to each session in a Latin-square sequence: unflavored water (W), grape-flavored water (FW), and grape-flavored water plus 6% carbohydrate and 18 mmol/l NaCl (CNa). Drinking was ad Libitum. Body weight, heart rate, rectal and skin temperatures, and thirst and stomach fullness perceptions were monitored periodically. Total intake was 610, 882, and 1,157 g in W, FW, and CNa, respectively (CNa-W and CNa-FW; P < 0.05). Hypohydration was observed with W (-0.65% body wt) and FW (-0.32% body wt), but drinking CNa resulted in slight overhydration (+0.47% body wt, CNa-W, CNa-FW; P < 0.05). Other physiological and all perceptual variables were insignificantly different among trials. In conclusion, while flavoring of water reduces children's voluntary dehydration, further addition of 6% carbohydrates and 18 mmol/l NaCl prevents it altogether.