Saliva flow rate, total protein concentration and osmolality as potential markers of whole body hydration status during progressive acute dehydration in humans.

OBJECTIVE: To identify whether saliva flow rate, total protein concentration and osmolality are sensitive non-invasive markers of whole body hydration status, we compared changes in these parameters with changes in body mass during progressive acute dehydration.
DESIGN: Twelve euhydrated males reported to the laboratory following an overnight fast and cycled on a stationary ergometer at 60% maximal oxygen uptake in an environmental chamber (30 degrees C and 70% RH) until progressive body mass loss (BML) of 1.1+/-0.0, 2.0+/-0.0 and 2.9+/-0.2%. After exercise, subjects were given a volume of carbohydrate electrolyte solution equivalent to 150% BML to consume within 1h. Unstimulated whole saliva samples were collected over a 2 min period into pre-weighed tubes at pre-exercise, 1.1, 2.0 and 2.9% BML and then at 75, 135 and 195 min post-exercise.
RESULTS: Saliva total protein concentration and osmolality increased and flow rate decreased (P<0.01) during dehydration. Saliva total protein concentration and osmolality correlated strongly with % BML during dehydration (mean r=0.97 and 0.94, respectively: P<0.01). The correlation for saliva total protein concentration with % BML was greater (P<0.05) than the correlation for saliva flow rate with % BML (mean r=-0.88: P<0.01) during dehydration.
CONCLUSIONS: These data show that changes in saliva total protein concentration and osmolality, and to a lesser extent flow rate, are strongly associated with changes in body mass during progressive acute dehydration.