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.