Saliva indices track hypohydration during 48h of fluid restriction or combined fluid andenergy restriction.

OBJECTIVE: To investigate whether unstimulated whole saliva flow rate (UFR) and osmolality (Sosm) track changes in hydration status during 48h of restricted fluid intake (RF) or combined fluid and energy restriction (RF+RE). Following the 48h periods, UFR and Sosm were assessed after acute exercise dehydration and rehydration. DESIGN: Thirteen healthy males completed three trials in a randomised order: control (CON) where participants received their estimated energy (12,154+/-230kJ/d: mean+/-S.E.M) and fluid (3912+/-140ml/d) requirements, RF trial where participants received their energy requirements and 193+/-19ml/d water to drink (total fluid 960+/-15ml/d) and RF+RE where participants received 1214+/-25kJ/d and 962+/-16ml/d. After 48h, participants completed 30min of maximal exercise followed by rehydration (0-2h) and refeeding (2-6h). RESULTS: At 48h body mass loss exceeded 3% on RF and RF+RE. UFR decreased during 48h on RF (510+/-122 to 169+/-37microl/min) and RF+RE (452+/-92 to 265+/-53microl/min) and was lower than CON at 48h (441+/-90microl/min: P<0.05). Sosm increased during 48h on RF (54+/-3 to 73+/-5mOsmol/kg) and RF+RE (52+/-3 to 68+/-5mOsmol/kg) and was greater than CON at 48h (52+/-2mOsmol/kg: P<0.05). Unlike UFR, Sosm identified the additional hypohydration associated with exercise (P<0.05) and returned to within 0h values with rehydration. CONCLUSIONS: Sosm, and to a lesser extent UFR, track hydration status during a 48h period of RF or RF+RE and after subsequent exercise and rehydration.