New Salivary Markers of Hydration Compare Favorably with Plasma and Urine Osmolality During Acute Dehydration

Abstract

1667 PURPOSE: To identify whether saliva osmolality, total protein concentration and flow rate are sensitive non-invasive markers of hydration status we compared changes in these parameters with changes in plasma osmolality (Posmo) during progressive acute dehydration. METHODS: Sixteen euhydrated males (Posmo: 289 ± 1 mOsmol. kg−1, mean ± SEM) exercised (30°C, 70% RH) until progressive body mass loss (BML) of 1, 2 and 3%. Venous blood, urine and 2-min unstimulated saliva samples were collected at pre-exercise, 1, 2 and 3% BML. Saliva flow rate was determined by dividing the volume of saliva by the collection time. Saliva total protein concentration was determined using the Coomassie blue technique. Osmolality was measured using a freezing point depression Osmometer. RESULTS: Plasma, urine and saliva osmolality increased, as did saliva total protein concentration, during dehydration (Posmo at 3% BML: 298 ± 1 mOsmol.kg−1: urine osmolality at pre-exercise: 385 ± 67; 3% BML: 737 ± 42 mOsmol.kg−1, P< 0.01). Saliva osmolality increased from 49 ± 3 at pre-exercise to 105 ± 11 mOsmol.kg−1 at 3% BML. Saliva flow rate decreased during dehydration (preexercise: 432 ± 77; 3% BML: 159 ± 41 μl.min−1, P< 0.01). Saliva osmolality, urine osmolality and saliva total protein concentration each correlated strongly with Posmo during dehydration (r = 0.86, r = 0.80 and r = 0.90, P< 0.01) with no significant difference between the correlation coefficients. The correlations for saliva osmolality, urine osmolality and saliva total protein concentration with Posmo were greater (P< 0.01) than the correlation for saliva flow rate with Posmo during dehydration (r = −0.75, P< 0.01). CONCLUSIONS: These results show that saliva osmolality and total protein concentration, and to a lesser extent flow rate, are sensitive to changes in hydration status during progressive acute dehydration. Additionally, saliva osmolality and total protein concentration are as sensitive to changes in hydration status during progressive acute dehydration as urine osmolality.