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


METHODS
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.
Oliver
Samuel J
SJ
School of Sport, Health and Exercise Sciences, Bangor University, Bangor LL57 2PZ, UK. s.j.oliver@bangor.ac.uk
Laing
Stewart J
SJ
Wilson
Sally
S
Bilzon
James L J
JL
Walsh
Neil P
NP
D015415:Biomarkers / Q000378:metabolism; D003681:Dehydration / Q000175:diagnosis*; D002149:Energy Intake / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005440:Fluid Therapy; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009994:Osmolar Concentration; D012463:Saliva / Q000378:metabolism*; D012472:Salivation / Q000502:physiology; D014868:Water Deprivation / Q000502:physiology; D015431:Weight Loss; D055815:Young Adult
D015415:Biomarkers